Publications Supported by the Blake-Nuttall Fund
Arnold, J.M., I.C.T. Nisbet, and R. Veit. 2011. Assessing aural and visual curing as tools for seabird management. Journal of Wildlife Management. 75:495-500.
Abstract: Social attraction, that is, mimicking of active and productive colonies via audio playback of calls of breeding conspecifics and the use of decoys, is commonly used to attract birds to newly established or restored breeding sites. However, little is known about the relative importance of aural versus visual cues for identify nesting areas. Such information is important for design and evaluation of management protocols. We studied the effectiveness of decoys (visual cues) and playbacks (audio cues) as methods for restoring a colony of common terns (Sterna hirundo) at Muskeget Island, Massachusetts, USA. We used a 2-year, crossover experiment with 3 treatment areas: audio and visual, audio only, and visual only. We reversed treatment areas in the second year to control for previous nesting area or substrate preference. In both years, nests were built 9-101 m downwind of loudspeakers. There was no overlap in areas used for nesting between years and no nests were built within decoy plots in either year. Behavioral observations showed that birds responded to decoys only when within range of sound treatments. Conspecific vocalizations appear to be important proximate cues for seabird colony site selection and should be given priority in management protocols using social attraction.
Balakrishnan, C.N., and S.V. Edwards. 2009. Nucleotide variation, linkage disequilibrium and founder-facilitated speciation in wild populations of the zebra finch (Taeniopygia guttata). Genetics 181:645-660.
Abstract: The zebra finch has long been an important model system for the study of vocal learning, vocal production, and behavior. With the imminent sequencing of its genome, the zebra finch is now poised to become a model system for population genetics. Using a panel of 30 noncoding loci, we characterized patterns of polymorphism and divergence among wild zebra finch populations. Continental Australian populations displayed little population structure, exceptionally high levels of nucleotide diversity (pi = 0.010), a rapid decay of linkage disequilibrium (LD), and a high population recombination rate (rho approximate to 0.05), all of which suggest an open and fluid genomic background that could facilitate adaptive variation. By contrast, Substantial divergence between the Australian and Lesser Sunda Island populations (K(ST) = 0.193), reduced genetic diversity (pi = 0.002), and higher levels of LD in the island Population suggest a strong but relatively recent founder event, which may have contributed to speciation between these populations as envisioned under founder-effect speciation models. Consistent with this hypothesis, we find that tinder a simple quantitative genetic model both drift and selection could have contributed to the observed divergence in six quantitative traits. In both Australian and Lesser Sundas populations, diversity in Z-linked loci was significantly lower than in autosomal loci. Our analysis provides a quantitative framework for studying the role of selection and drift in shaping patterns of molecular evolution in the zebra finch genome.
Barnett, J.M., and D.R.C. Buzzetti. 2014. A new species of Chichlocolaptes Reichenbach 1853 (Furnariidae), the ‘gritador-do-nordeste-, an undescribed trace of the fading bird life of northeastern Brazil. Revista Brasileira de Ornithologia 22(2): 75-94.
Abstract: A new species of treehunter, Cichlocolaptes mazarbarnetti sp. nov., is described from a specimen that for many years had been confused with Philydor novaesi. The morphology of this specimen, collected in 1986 at Pedra Branca, Murici, Alagoas, at 550 m elevation (currently the Murici Ecological Station), suggests its allocation in the genus Cichlocolaptes. The new species differs from P. novaesi by its considerably larger size, heavier body-mass, darker and more uniform forehead and crown, absence of buffy periocular-feathers, and a pale orange-rufous tail that contrasts with the rump and the rest of the dorsal plumage. It also has a flat-crowned appearance and a larger, deeper-based, and generally stouter bill. Behavioral specialization on bromeliads and vocal repertoire also suggest that the new species belongs in the genus Cichlocolaptes. The song of this species is markedly different from that of P. novaesi, and it closely matches that of Cichlocolaptes leucophrus. The new species is endemic to the 'Pernambuco Center' of endemism, where it inhabits dense, humid forests in hilly terrain. It is known from only two localities in northeastern Brazil, one each in the states of Alagoas and Pernambuco. Taken together, these areas contain less than 3,000 ha of suitable habitat for the species, where we estimate the population during our studies to have numbered no more than 10 individuals. We propose that this species should be categorized as Critically Endangered at a national and global level, and we consider the situation of its conservation to be critical in that it will require urgent action to avoid its global extinction.
Byers, B.E., Akresh, M.E. and King, D.I. 2015. A proxy of social mate choice in prairie warblers is correlated with consistent, rapid, low-pitched singing. Behavioral Ecology and Sociobiology 69:1275-1286.
Abstract: In songbirds, female mate choice may be influenced by how well a male performs his songs. Performing songs well may be especially difficult if it requires maximizing multiple aspects of performance simultaneously. We therefore hypothesized that, in a population of prairie warblers, the males most attractive to females would be those with superior performance in more than one facet of singing. We tested this prediction by comparing different aspects of song performance, as well as different combinations of these aspects, to determine which were the best predictors of first-egg date, which we took to be a proxy for social mate choice. We found that first-egg date was best predicted by a combination of song performance traits that included consistent performance, rapid rate, and low pitch. Female preference for males capable of physically challenging song performance may have contributed to the evolution of acoustically complex vocalizations in oscine songbirds, because if complex sounds are more difficult to perform, they may be favored by selection for signal reliability.
Byers, B.E., Akresh, M.E. and King, D.I. 2016. Song and male quality in prairie warblers. Ethology 122:660-670.
Abstract: To determine if the songs of male prairie warblers could potentially reveal to female listeners information about the quality of singers, we compared various aspects of prairie warbler song structure and performance to attributes that might reflect a male singer's potential to enhance the fitness of his mate. We found that all the tested male attributes-arrival date, age, body size, annual survival, and fledging success-were associated with singing, most with multiple aspects of singing. Several of the song traits that were associated with potential indicators of male quality had also been found previously to be good predictors of female social mate choice. In particular, longer songs with longer elements, performed at lower frequency and with greater consistency, were associated with both female mate choice and potential indicators of quality. Thus, female prairie warblers may assess potential mates with the help of a set of song characteristics that collectively reveal an array of attributes that together indicate overall male quality.
Cava, J.A., Perlut, N.G. and Travis, S.E. 2016. Why come back home? Investigating the proximate factors that influence natal philopatry in migratory passerines. Animal Behaviour 118:39-46.
Abstract: Knowledge of which cues attract birds back to natal areas is important for conservation because the cues could be manipulated to attract breeders to source habitat or discourage breeders from settling in sink habitat. We examined the influence of intrinsic and extrinsic variables on natal philopatry using two metrics, short-distance natal dispersal and the probability of philopatry to the natal field, in two obligate-grassland bird species breeding in an agricultural landscape: the bobolink, Dolichonyx oryzivorus, and the Savannah sparrow, Passerculus sandwichensis. During 2002-2014, we detected 90 locally hatched Savannah sparrows and 129 locally hatched bobolinks breeding as adults near their places of origin (mean +/- SD dispersal distances: Savannah sparrows: 917 +/- 851 m; bobolinks: 1251 +/- 839 m). For both species, the location of the field on which they bred relative to fields where annual productivity was greater than replacement best explained variation in natal dispersal distance. The probability a Savannah sparrow was philopatric to its natal field increased if it fledged later in the season, while this probability decreased if there was an opposite-sex parent or sibling present on the natal field, or the field was under a late-hay management scheme. None of the variables considered explained variation in bobolink natal philopatry. Natal philopatry and short-distance natal dispersal in these species appear to be influenced by factors that are difficult to manage; however, land managers should attempt to keep management consistent across time to reduce misinformation in dispersal cues.
Cava, J.A., Perlut, N.G. and Travis, S.E. 2019. Heritability and evolvability of morphological traits of Savannah sparrows (Passerculus sandwichensis) breeding in agricultural grasslands. PloS One 14:e0210472.
Abstract: Heritability and evolvability estimates of adult traits from free-living bird populations can be used to gauge the ability of populations to respond to selection, but are rare due to difficulties in gathering detailed pedigree information. The capacity to respond to selection is particularly important for species occupying managed habitats such as agricultural grasslands because of the potential for humans to accidentally influence traits. We calculated heritability and evolvability of six morphological traits in a population of Savannah Sparrows (Passerculus sandwichensis) breeding in a large agricultural landscape. We used microsatellite analysis to determine a genetic pedigree, revealing a high level of extra-pair paternity (63%) within a relatively philopatric population. For the entire population, heritabilities varied from low to high (bill width: 0.160 +/- 0.182 to tarsus length: 0.651 +/- 0.155), while evolvabilities were low across all traits (wing length: 0.035 +/- 0.013 to body mass: 0.066 +/- 0.106). Our results indicate that any directional selection from agricultural management practices will produce negligible changes in basic morphometrics of Savannah sparrow populations occupying the Champlain Valley of Vermont, USA.
Cornell, A., Melo, M., Zimmerman, C. and Therrien, J.F. 2021. Nestling Physiology Is Independent of Somatic Development in a Common Raptor, the American Kestrel (Falco sparverius). Physiological and Biochemical Zoology 94: 99-109.
Abstract: Although many studies have documented the developmental trajectory of somatic traits in birds, few measure physiological traits, and even fewer document individual variation in developmental trajectory across ecological context. Hematological traits underlying aerobic capacity can be predictive of nestling survival, fledgling flight ability, and ultimately recruitment. This study aimed to assess individual variation in the developmental trajectory of two physiological traits that underlie aerobic capacity, hematocrit and hemoglobin concentration, in relation to somatic development and ecological context. Our study species, the American kestrel (Falco sparverius), is sexually dimorphic and therefore likely to show sexual variation in developmental trajectory and nestling maturity. We used lay date, year, brood size, nestling sex ratio, and parental nest visit rate to assess ecological context. Although somatic traits showed similar trajectories across nestlings, developmental trajectory for hematocrit and hemoglobin concentration showed individual variation not previously documented. This individual variation in developmental change, or trajectory, for physiological traits could not be explained by somatic development, sex, parental nest visit rate, lay date, year, brood size, or nestling sex ratio. However, we did find higher final hemoglobin concentration in 2018 and in nests with earlier lay dates. These findings demonstrate the importance of assessing physiological traits that capture aspects of individual quality distinct from somatic traits. Future studies are needed to understand the causes of individual variation in developmental trajectory, which cannot be explained by the ecological variables presented here, and the potential fitness consequences of this variation.
DaCosta, J.M., Miller, M.J., Mortensen, J.L., Reed, J.M., Curry, R.L. and Sorenson, M.D. 2019. Phylogenomics clarifies biogeographic and evolutionary history, and conservation status of West Indian tremblers and thrashers (Aves: Mimidae). Molecular Phylogenetics and Evolution 136:196-205.
Abstract: The West Indian avifauna has provided fundamental insights into island biogeography, taxon cycles, and the evolution of avian behavior. Our interpretations, however, should rely on robust hypotheses of evolutionary relationships and consistent conclusions about taxonomic status in groups with many endemic island populations. Here we present a phylogenetic study of the West Indian thrashers, tremblers, and allies, an assemblage of at least 5 species found on 29 islands, including what is considered the Lesser Antilles' only avian radiation. We improve on previous phylogenetic studies of this group by using double-digest restriction site-associated DNA sequencing (ddRAD-seq) to broadly sample loci scattered across the nuclear genome. A variety of analyses, based on either nucleotide variation in 2223 loci recovered in all samples or at 13,282 loci confidently scored as present or absent in all samples, converged on a single well-supported phylogenetic hypothesis. Results indicate that the resident West Indian taxa form a monophyletic group, exclusive of the Neotropical-Nearctic migratory Gray Catbird Dumetella carolinensis, which breeds in North America; this outcome differs from earlier studies suggesting that Gray Catbird was nested within a clade of island resident species. Thus, our findings imply a single colonization of the West Indies without the need to invoke a subsequent 'reverse colonization' of the mainland by West Indian taxa. Additionally, our study is the first to sample both endemic subspecies of the endangered White-breasted Thrasher Ramphocinclus brachyurus. We find that these subspecies have a long history of evolutionary independence with no evidence of gene flow, and are as genetically divergent from each other as other genera in the group. These findings support recognition of R. brachyurus (restricted to Martinique) and the Saint Lucia Thrasher R. sanctaeluciae as two distinct, single-island endemic species, and indicate the need to re-evaluate conservation plans for these taxa. Our results demonstrate the utility of phylogenomic datasets for generating robust systematic hypotheses.
DesRochers, D. W., L. K. Butler, M. D. Silbernagle, and J. M Reed. 2009. Observations of molt in an endangered rallid, the Hawaiian Moorhen. Wilson Journal of Ornithology 121:148-153.
Abstract: We used field and museum data to describe timing of flight feather molt in the endangered Hawaiian Moorhen (Gallinula chloropus sandvicensis). We evaluated 80 adults captured a total of 107 times at two study sites on Oahu from April 2005 to August 2007. Eighty-five of the birds were not molting, 13 had abraded remiges, and eight of the nine molting adults examined were simultaneously replacing their primaries, secondaries, and upper and lower wing coverts. We also scored molt for 28 Hawaiian Moorhen specimens from three museum collections, but no birds were molting. Molt in Hawaiian Moorhens, which lasts about 30 days, was not synchronous across individuals with molting birds recorded from June to September in the field. We observed non-molting individuals throughout the year including birds we captured and museum specimens. Molting and nonmolting birds had similar body condition, as defined by mass/tarsometatarsal length. The flightless period during molt, which likely lasts about 25 days, may increase predation risk, a serious concern in Hawaii where introduced terrestrial predators pose a major threat to moorhen populations.
Desrochers, D. W., S. R. McWilliams, M. D. Silbernagle, and J. M Reed. 2009. Macronutrient profiles of wetland plants consumed by the Hawaiian Moorhen (Gallinula chloropus sandvicensis). Wetlands 29:845-853.
Abstract: Understanding the nutritional quality of wildlife foods is important for management and conservation efforts. We report the gross energy and macronutrient content of 10 plant species consumed by endangered Hawaiian Moorhens (Gallinula chloropus sandvicensis) along with gross energy and macronutrient content of three plant species not known to be consumed by moorhen. We also report the same information for Urochloa mutica that is consumed when it is 10 cm tall, but not when it is taller. We also compared macronutrient composition of plant species collected from sites with different soil moisture levels. Energy density, fat, ash, nitrogen, protein, carbohydrates, and fiber of these wetland plants were similar across soil moisture categories, but differed among plant species. We tested for rank consistency of nutrient values across species to determine if some were consistently high across measures, and we tested whether there were differences in energy and protein content between natives and nonnatives, and between species consumed versus not eaten. Rank values of macronutrients were inconsistent across species, and we found no differences in energy or protein across groups of species. Information on Hawaiian Moorhen nutritional requirements and the species’ ability to metabolize these different plants will help inform wetland managers.
DesRochers, D.W., S. R. McWillaims, and J. M. Reed. 2010. Evaluating if energy and protein limit abundance of Hawaiian Moorhen (Gallinula chloropus sandvicensis). Journal of Wildlife Management 74:788-795.
Abstract: Food abundance can affect a species’ distribution. In many studies of potential food limitation, researchers focus on carrying capacity estimates during the nonbreeding season for temperate species consuming a fixed food source. Estimates of energetic carrying capacity for year-round breeders feeding on a replenishing resource would be more difficult and require much data. To determine whether gathering detailed information on year-round carrying capacity would be an important investment, we conducted an assessment to determine whether there was evidence that energy or protein might limit numbers of the tropical, endangered Hawaiian moorhen (Gallinula chloropus sandvicensis). We compared observed numbers of moorhen at 15 Oahu, Hawaii, USA, wetlands with predicted numbers based on measured energy and protein in food plants and abundance of these food plants in each wetland and on estimates of energy expenditure of moorhen. We made comparisons assuming moorhen are limited by their ability to metabolize food plants, by competition for food, and by estimated costs associated with reproduction. We also compared ranked moorhen abundance and density with ranked energy and protein under different wetland management regimes. Energy values consistently overestimated expected numbers of Hawaiian moorhen at wetlands except for one wetland location (predicted, 3803 - 4856; observed, 6.2 - 10.8). In addition, we detected no significant relationship between moorhen abundance and measures of energy (all r2 > 0.02–0.73, all P < 0.1) or protein abundance (all r2 > 0.08–0.50, all P < 0.3). This lack of relationship held once we controlled for wetland area or when we considered whether wetlands were managed for waterbirds. Hawaiian moorhen on Oahu did not appear to be limited by energy, nor did they appear to select sites based on energy or protein, in contrast to many studies relating animal numbers to energy in nonbreeding situations. Consequently, we suggest that researchers and managers explore other potentially limiting factors for Hawaiian moorhen.
Frey, S.J.K., C.C. Rimmer, K.P. McFarland, and S. Menu. 2008. Identification and sex determination of Bicknell’s thrushes using morphometric data. Journal of Field Ornithology 79:408-420.
Abstract: The similar plumage of Bicknell's (Catharus bicknelli) and Gray-cheeked (C. minimus) Thrushes have hindered attempts to better understand the nonbreeding biology of these species. We used morphometric data, specifically primary formulae, from Bicknell's Thrushes of known sex and age throughout their breeding range in the United States and Canada to examine possible differences between sex and age classes. We compared these data with similar data from Gray-cheeked Thrushes in Alaska, United States and Newfoundland, Canada to examine mensural characters for distinguishing the two species. We performed a discriminant function analysis (DFA) for each age class to examine morphometric differences between male and female Bicknell's Thrushes. For second-year (SY) and after-second-year (ASY) birds, wing chord was the strongest differentiator, in conjunction with tarsus length. Wing chord and tail length were used to create a discriminant function to differentiate between the two Catharus species. The discriminant functions for both age classes did not permit unambiguous separation of male and female Bicknell's Thrushes nor did the DFA enable unequivocal species identity, but most individuals were correctly classified. Significant differences in the p8-p1 measurement of Bicknell's and Gray-cheeked Thrushes and of male and female Bicknell's Thrushes suggest that this character may be useful to augment published wing chord criteria for species identification and sex determination. Our results indicate that wing chord, in combination with tail length, is the most useful measurement for distinguishing Bicknell's from Gray-cheeked Thrushes and, when augmented with tarsus length, to differentiate between male and female Bicknell's Thrushes outside the breeding season.
Gallinat, A.S., Primack, R.B. and Lloyd-Evans, T.L. 2020. Can invasive species replace native species as a resource for birds under climate change? A case study on bird-fruit interactions. Biological Conservation 241:108268.
Abstract: Wild fruits are an important food source for many north temperate-breeding landbirds during autumn migration and, in turn, birds provide the service of seed dispersal. Despite the importance of these autumn interactions, their potential to shift with climate change and species invasions remains poorly understood. As invasive fleshy-fruited shrubs spread across the Northeast USA and many landbird species pass through stopover sites later with warming temperatures, the potential for changes in bird-fruit interactions depends on the phenology and availability of native and invasive wild fruits, and bird preferences across the autumn season. We observed the fruiting phenology of 25 native and invasive fleshy-fruited wild plant species at Manomet, a migratory stopover site on the coast of Massachusetts, USA, during the autumn migration season (August to November) in 2014 and 2015. We also monitored fruit availability across Manomet in 2015. To determine whether fruit consumption reflected phenology and availability, we identified seeds from 469 fecal samples collected from songbirds captured during the 2014 and 2015 autumn banding seasons. We found that while invasive shrubs fruited later, on average, than native plants, and comprised a large proportion of the total available fruits in late-autumn, birds primarily consumed the fruits of native species throughout the autumn season. Our results demonstrate that native fruits are an important food resource for birds during the autumn migration season and are unlikely to be replaced by abundant fruits of late-season invasive species under climate change.
Gormally, B.M., van Rees, C.B., Bowers, E., Reed, J.M. and Romero, L.M. 2020. Feather corticosterone does not correlate with environmental stressors or body condition in an endangered waterbird. Conservation Physiology 8:coaa125.
Abstract: Physiological metrics are becoming popular tools for assessing individual condition and population health to inform wildlife management and conservation decisions. Corticosterone assays can provide information on how animals cope with individual and habitat-level stressors, and the recent development of feather assays is an exciting innovation that could yield important insights for conservation of wild birds. Due to the widespread enthusiasm for feather corticosterone as a potential bioindicator, studies are needed to assess the ability of this technique to detect meaningful differences in physiological stress across a variety of stressor types and intensities. We examined feather corticosterone from 144 individuals among the 13 known breeding populations of Hawaiian gallinule (Gallinula galeata sandvicensis), an endangered waterbird, on the island of O'ahu. These ecologically independent subpopulations are known to have low genetic connectivity and movement rates and differ largely across a number of important conditions, including level of predator management, human disturbance, proximity to urban development and conspecific population density. This system is well suited for assessing the performance of feather corticosterone as a bioindicator of different known habitat-level threats common to this and many other conservation-reliant species. We found no statistically significant relationship between feather corticosterone and level of predator control, level of human disturbance, gallinule population density, percent urban cover or body condition across all sites despite the substantial difference in stressor magnitude in our dataset. We did find that gallinules in habitats with larger population densities were in worse body condition. These findings suggest that feather corticosterone is not a consistent indicator of anthropogenic impacts on populations. Furthermore, they suggest that feather corticosterone may be a poor bioindicator of known habitat-level threats for Hawaiian gallinules and that it should be used with caution in other avian taxa of conservation concern.
Goyert, H.F. 2015. Foraging specificity and prey utilization: evaluating social and memory-based strategies in seabirds. Behaviour 152:861-895.
Abstract: This study explores the capacity for seabirds to exhibit behavioral plasticity in response to the predictability of resources. Using direct species-comparisons, I tested the hypothesis that roseate terns (Sterna dougallii), dietary specialists, rely more heavily on foraging site-fidelity to pursue persistent prey, whereas common terns (S. hirundo), prey generalists, depend more on local enhancement by exploiting mixed-species assemblages. I analysed chick-provisioning observations and the bearings of commuting trajectories between the shared breeding colony, foraging areas, and feeding flocks. Foraging route patterns in roseate terns were consistent with a strategy based more heavily on spatial memory than social cues, in contrast to common terns, which associated more readily with nearby feeding aggregations, in line with social facilitation. Only during years of high prey abundance did roseate terns outperform common terns in nest productivity and the quality of prey delivered to chicks, suggesting that opportunistic tactics support resilience to sparse prey availability.
Hennessey, A.B. 2011. Species rank of Phibalura (Flavirostris) boliviana based on plumage, soft part color, vocalizations, and seasonal movements. Wilson Journal of Ornithology 123:454-458.
Abstract: The Swallow-tailed Cotinga (Phibalura flavirostris) has traditionally been considered to consist of two subspecies, P. f. flavirostris of southeastern Brazil's foothill forest and, isolated by similar to 2,500 km, a population of P. f. boliviana in central-western Bolivia. The plumage of the two taxa is distinctly different; boliviana males have a longer tail, and body plumage is significantly less sexually dimorphic. The iris of boliviana is mustard yellow, distinct from the blood red iris of flavirostris. P. f. boliviana has dull to bright orange-yellow feet whereas flavirostris has pink feet. Only one vocalization type is recorded for P. f. flavirostris, whereas at least five calls and a song are known for P. f. boliviana, which vocalizes significantly more often. The Brazilian P. f. flavirostris has strong seasonal movements, whereas P. f. boliviana has no seasonal movements. Given the diagnosable differences between the two taxa, it is highly probable they are separate lineages. P. boliviana qualifies as critically endangered for its declining small population due to continual habitat loss.
Kamm, M. and Reed, J.M. 2020. Assessing microhabitat characteristics as predictors of nest-box occupancy in a declining bird species, the American Kestrel (Falco sparverius). Northeastern Naturalist 27:344-357.
Abstract: Falco sparverius (American Kestrel) is a declining species that readily uses human-provided nest boxes. We test several hypotheses from the literature regarding nest microhabitat preferences of American Kestrels, including putative preferences for brighter cavities and cavities with a given compass orientation, both of which are believed to provide some thermal benefit. We placed light and temperature data loggers in 26 nest boxes in Massachusetts after young had fledged from occupied boxes. Cavity interior light and temperature were not correlated, and while nest-box orientation did affect cavity interior light levels, none of these variables was significantly associated with occupancy. Micro-habitat variables may be more important in some geographic areas than in others; the results of our study suggest that existing hypotheses need experimental verification. It is possible that multi-region studies integrating the effects of ambient temperature and wind on cavity selection will better explain apparent differences in microhabitat preferences across the species' range.
Keyel, A. C., C. M. Bauer, C. R. Lattin, L. M. Romero, J. M. Reed. 2012. Testing the role of patch openness as a causal mechanism for apparent area sensitivity. Oecologia 169:407-418.
Abstract: Area sensitivity, species being disproportionately present on larger habitat patches, has been identified in many taxa. We propose that some apparently area-sensitive species are actually responding to how open a habitat patch is, rather than to patch size. We tested this hypothesis for Bobolinks (Dolichonyx oryzivorus) by comparing density and occupancy to a novel openness index, patch area, and edge effects. Bobolink density and occupancy showed significant relationships with openness, but logistic models based on an openness occupancy threshold had greater explanatory power. Thresholds remained approximately consistent from June through August, and shifted to be more open in September. Variance partitioning supported the openness index as unique and relevant. We found no relationships between measures of body condition (body mass, body size, circulating corticosterone levels) and either openness or area. Our findings have implications for studies of area sensitivity, especially with regards to inconsistencies reported within species: specifically, (1) whether or not a study finds a species to be area sensitive may depend on whether small, open sites were sampled, and (2) area regressions were sensitive to observed densities at the largest sites, suggesting that variation in these fields could lead to inconsistent area sensitivity responses. Responses to openness may be a consequence of habitat selection mediated by predator effects. Finally, openness measures may have applications for predicting effects of habitat management or development, such as adding wind turbines, in open habitat.
Keyel, A. C., D.T. Peck, and J. M. Reed. 2012. No evidence for individual assortment by temperament relative to patch area or patch openness in Bobolinks. Condor 114:212-218.
Abstract: Recent research has shown repeatable individual variability in temperament traits. We tested the hypotheses that individual Bobolinks (Dolichonyx oryzivorus) vary consistently in their response to predators, a temperament trait, and that this individual variation is associated with breeding-site selection. Specifically, we tested whether measures of behavioral response to human approaches are associated with either patch area or patch openness and thus to area sensitivity. We made two to seven sequential approaches to Bobolinks in 2009 and 2010, measuring starting distance, flight-initiation distance, and the distance from the observers to where the birds landed. We analyzed the data with repeatability estimates and linear mixed modeling. Flight-initiation distance was repeatable when starting distance was controlled for, but distance to landing was not after starting distance and flight-initiation distance were controlled for. We found no strong effect of area or openness on either flight initiation distance or distance to landing. We conclude that this measure of response to predators shows individual variation, but this variation does not explain patterns of settlement among habitat patches. Because flight-initiation distance is often used to identify distances at which human behavior disrupts wildlife, we estimate its mean (21.8 m) and the distance at which 75%, 95%, and 99% of the Bobolinks flushed (28, 40, and 59 m, respectively).
Linck, E., Bridge, E.S., Duckles, J.M., Navarro-Sigüenza, A.G. and Rohwer, S. 2016. Assessing migration patterns in Passerina ciris using the world’s bird collections as an aggregated resource. PeerJ 4:e1871.
Abstract: Natural history museum collections (NHCs) represent a rich and largely untapped source of data on demography and population movements. NHC specimen records can be corrected to a crude measure of collecting effort and reflect relative population densities with a method known as abundance indices. We plotted abundance index values from georeferenced NHC data in a 12-month series for the new world migratory passerine Passerina ciris across its molting and wintering range in Mexico and Central America. We illustrated a statistically significant change in abundance index values across regions and months that suggests a quasi-circular movement around its non-breeding range, and used enhanced vegetation index (EVI) analysis of remote sensing plots to demonstrate non-random association of specimen record abundance with areas of high primary productivity. We demonstrated how abundance indices from NHC specimen records can be applied to infer previously unknown migratory behavior, and be integrated with remote sensing data to provide a deeper understanding of demography and behavioral ecology across time and space.
Lindemann, E.S., Harris, J.P. and Keller, G.S. 2015. Effects of vegetation, landscape composition, and edge habitat on small-mammal communities in northern Massachusetts. Northeastern Naturalist 22:287-298.
Abstract: In southern New England forests, small mammals provide essential contributions to ecosystem functioning via food-web interactions and seed dispersal. This region has been exposed to extensive habitat fragmentation due to residential and agricultural development, resulting in a considerable amount of edge habitat, in addition to naturally occurring landscape heterogeneity. Limited research has been conducted relating small-mammal species richness and abundance to different types of edge habitat in this region. Studies incorporating an analysis of variation in both fine-scale vegetation and coarse-scale landscape variation are even more limited. We compared small-mammal richness, total abundance, and abundance of Peromyscus maniculatus (Deer Mouse), Peromyscus leucopus (White-footed Mouse), Myodes gapperi (Red-backed Vole), Tamias striatus (Eastern Chipmunk), and Tamiasciurus hudsonicus (Eastern Red Squirrel) at developed-edge, wetland-edge, and forest-interior sites. We also measured vegetation and landscape variables to understand how variation in characteristics at different scales affected small-mammal measures. We selected 4 sites of each edge type and used Sherman live-traps during the summers of 2009-2010 to survey small-mammal populations (75 traps for 4 nights at 12 sites for 2 y = 7200 trap-nights). We did not find differences among edge types and interior forest for total abundance, richness, and abundance of the 5 small-mammal species with sufficient data for analysis. However, vegetation variables and landscape variables were significantly associated with small-mammal populations. Step-wise linear regression included vegetation variables for 4 of the 5 species, and various landscape scales were included in all analyses except abundance of Peromyscus adults. Patch size was included in 4 analyses (positive for total abundance, White-footed Mouse, and Red-backed Vole; negative for Eastern Chipmunk). We found conifer basal area to have a positive relationship with abundance of Peromyscus adults and Red-backed Voles, but a negative relationship with abundance of Peromyscus juveniles and Eastern Red Squirrels. Species abundance and richness of small-mammal communities and populations in northeastern Massachusetts were related to both fine-scale vegetation differences and coarse-scale landscape metrics, but these relationships were complex and scale-dependent.
McFarland, K.P., Rimmer, C.C., Goetz, J.E., Aubry, Y., Wunderle, J.M. Jr., et al. 2013. A winter distribution model for Bicknell’s thrush (Catharus bicknelli), a conservation tool for a threatened migratory songbird. PLoS ONE 8(1): e53986.
Abstract: Conservation planning and implementation require identifying pertinent habitats and locations where protection and management may improve viability of targeted species. The winter range of Bicknell’s Thrush (Catharus bicknelli), a threatened Nearctic-Neotropical migratory songbird, is restricted to the Greater Antilles. We analyzed winter records from the mid-1970s to 2009 to quantitatively evaluate winter distribution and habitat selection. Additionally, we conducted targeted surveys in Jamaica (n = 433), Cuba (n = 363), Dominican Republic (n = 1,000), Haiti (n = 131) and Puerto Rico (n = 242) yielding 179 sites with thrush presence. We modeled Bicknell’s Thrush winter habitat selection and distribution in the Greater Antilles in Maxent version 3.3.1. using environmental predictors represented in 30 arc second study area rasters. These included nine land form, land cover and climatic variables that were thought a priori to have potentially high predictive power. We used the average training gain from ten model runs to select the best subset of predictors. Total winter precipitation, aspect and land cover, particularly broadleaf forests, emerged as important variables. A five-variable model that contained land cover, winter precipitation, aspect, slope, and elevation was the most parsimonious and not significantly different than the models with more variables. We used the best fitting model to depict potential winter habitat. Using the 10 percentile threshold (>0.25), we estimated winter habitat to cover 33,170 km2, nearly 10% of the study area. The Dominican Republic contained half of all potential habitat (51%), followed by Cuba (15.1%), Jamaica (13.5%), Haiti (10.6%), and Puerto Rico (9.9%). Nearly one-third of the range was found to be in protected areas. By providing the first detailed predictive map of Bicknell’s Thrush winter distribution, our study provides a useful tool to prioritize and direct conservation planning for this and other wet, broadleaf forest specialists in the Greater Antilles.
Miller-Rushing, A.J., R.B. Primack, & R. Stymeist. 2008. Interpreting variation in bird migration times as observed by volunteers. Auk 125:565-573.
Abstract: As a result of changes in climate over the past 100 years, many birds are arriving at points along their migration routes earlier in the spring now than they did in the past. Increasingly, researchers are relying on a variety of data sources, such as naturalist journals and bird-club records, to document migration times. However, it is not clear whether researchers can successfully use different sources of data to compare changes in migration times. We examined 25 years of changes in migration times for 30 species of birds at Mt. Auburn Cemetery in Cambridge, Massachusetts, as documented by bird-club members and published in a regional bird journal. We found that, overall, birds arrived earlier in warmer springs in eastern Massachusetts. We compared our findings with those of previous studies in Massachusetts, which included data from a standardized bird-banding station and observations from a naturalist’s journal and bird-club records. On a species-by-species basis, changes in migration times were not correlated among the studies. We believe that local changes in population sizes and sampling effort at some of the sites may have contributed to the lack of correlation. For the purpose of comparing changes in migration times across species and locations, standardized bird-banding data are preferable to data collected by volunteer naturalists. However, naturalist data sources are useful and reflect the widely observed trend toward earlier migrations in warm springs.
Murray, M. 2011. Anticoagulant rodenticide exposure and toxicosis in four species of birds of prey presented to a wildlife clinic in Massachusetts, 2006–2010. Journal of Zoo and Wildlife Medicine 42:88-97.
Abstract: Restrictions on second-generation anticoagulant rodenticides (SGARs) in the United States, which were partially implemented in 2011, prohibit the sale of SGAR products through general consumer outlets to minimize use by non-professional or non-agricultural applicators. This study analyzed liver tissue from four species of birds of prey admitted to a wildlife clinic in Massachusetts, USA, from 2012-2016 for residues of anticoagulant rodenticides (ARs). Ninety-four birds were analyzed; 16 were symptomatic for AR toxicosis, and 78 asymptomatic. Ninety-six percent of all birds tested were positive for SGARs: 100% of those diagnosed with AR toxicosis ante-mortem and/or post-mortem and 95% of subclinically exposed birds. Brodifacoum was found in 95% of all birds. Sixty-six percent of all birds contained residues of two or more SGARs. A significant increase in exposures to multiple SGARs occurred in later years in the study. Pesticide use reports (PURs) filed with the Massachusetts Department of Agricultural Resources were reviewed to determine the frequency of use of different ARs by pest management professionals (PMPs) across five years. This study finds that the three SGARs favored by PMPs-bromadiolone, difethialone, brodifacoum-were present in combination in the majority of birds, with increases in multiple exposures driven by increased detections of bromadiolone and difethialone. Continued monitoring of AR residues in nontarget species following full implementation of sales and packaging restrictions in the US is needed in order to elucidate the role of PMP use of SGARs in wildlife exposures and to evaluate the effectiveness of current mitigation measures.
Nisbet, U.C.T., C.S. Mostello, R.R. Veit, J.W. Fox, and V. Afanasyev. 2011. Migrations and winter quarter of five common terns tracked using geolocators. Waterbirds 34:32-39.
Abstract: Ten geolocators (light-level data loggers) were attached to Common Terns (Sterna hirundo) at a breeding site in the northeastern USA in 2007 and 2008; six were retrieved (five with useful data) in 2008 and 2009. The birds wintered in four discrete areas on the north and east coasts of South America, from Guyana (6-7 degrees N) to northeastern Argentina (36-42 degrees S); three remained within restricted areas for most or all of the winter, whereas two ranged more widely. They left the breeding area at various dates between 1 August and 14 September; three migrated directly from the breeding area while two first moved southwest to stage near Cape Hatteras. All five birds flew directly to the vicinity of Puerto Rico, then moved along the north and east coasts of South America, staging at scattered locations for periods of 3-11 d, before reaching their winter quarters at various dates from 6 September to 26 October. Two birds left their winter quarters on 2 March and 4 April, staged in northern Brazil for 47 and 6 d, then traveled via the Bahamas to reach the breeding site on 1 May. During breeding and post-breeding periods, the birds spent a mean of 7 min each day and virtually no time at night resting on the water, but during the rest of the year they often rested on the water for up to 6 h by day and up to 11 h at night. Leg-mounted geolocators caused several adverse effects but did not reduce survival.
Primack, R.B., and A.J. Miller-Rushing. 2012. Uncovering, collecting, and analyzing records to investigate the ecological impacts of climate change: a template from Thoreau's Concord. BioScience 62:170-181.
Abstract: Historical records are an important resource for understanding the biological impacts of climate change. Such records include naturalists' journals, club and field station records, museum specimens, photographs, and scientific research. Finding records and overcoming their limitations are serious challenges to climate change research. In the present article, we describe efforts to locate data from Concord, Massachusetts, and provide a template that can be replicated in other locations. Analyses of diverse data sources, including observations made in the 1850s by Henry David Thoreau, indicate that climate change is affecting the phenology, presence, and abundance of species in Concord. Despite recent work on historical records, many sources of historical data are underutilized. Analyses of these data may provide insights into climate change impacts and techniques to manage them. Moreover, the results are useful for communicating local examples of changing climate conditions to the public.
Pruitt, M., and K. G. Smith. 2016. History and fall migration of Northern Saw-whet Owls (Aegolius acadicus) in Arkansas. Journal of the Arkansas Academy of Science 70:190-198.
Abstract: The secretive Northern Saw-whet Owl (Aegolius acadicus) is believed to be much more widespread during fall and winter than previously thought in the southern United States. To see if they occur more frequently in Arkansas, we initiated a banding study in fall of 2014 in northwestern Arkansas. Prior to that, only 12 historic records existed for Arkansas between 1959 and 2010. Over the course of two field seasons, we captured and banded 24 Northern Saw-whet Owls in rural Madison County. All birds were mist-netted along a trail, in woodland composed of pine and cedar with fairly dense undergrowth. Two were captured during our 2014 season when we started in late November and 22 were captured between late October and early December in 2015. We also had at least 10 birds vocalizing at our site. It would appear that the peak of migration in Arkansas is late October through early November, with capture rates dropping off by early December. All but one of the captured birds were females, the most common sex this far south. There was a fairly even distribution of hatch-year, second-year, and after-second-year birds and hatch-year birds and adults arrived at about the same time in late October and early November in 2015. Exactly where the owls are migrating from is unknown, although three foreign recoveries in Missouri and four recoveries in Arkansas suggest they are coming from the western Great Lakes region. Once considered a vagrant, based on our research, the Northern Saw-whet Owl appears to be an uncommon fall migrant, at least in the northwestern part of Arkansas. Comparing our data with that for central Missouri, about the same number of birds were captured at the same rates for about the same length of time, suggesting that Northern Saw-whet Owls are probably more common in the Ozarks than previously thought.
Renfrew, R.B., D. Kim, N. Perlut, J. Smith, J. Fox, and P. P. Marra. 2013. Phenological matching across hemispheres in a long-distance migratory bird. Diveristy and Distributions 19:1008-1019.
Abstract: In the Northern Hemisphere, bird migration from the tropic to the temperate zone in spring is thought to proceed at a rate determined in large part by local phenology. In contrast, little is understood about where birds go or the factors that determine why they move or where they stop during the post-breeding period. Study sites were in Oregon, Nebraska and Vermont, and location data we collected extend south to Argentina. We deployed light-level geolocators on individual Bobolinks from three populations across the breeding range and compare their southbound movement phenology to austral greening as indicated by the Normalized Difference Vegetation Index. Bobolinks from all breeding populations synchronously arrived and remained for up to several weeks in two sequential, small non-breeding areas that were separated by thousands of kilometres, before staging for pre-alternate moult. Similar to the migration patterns of birds to northern breeding areas, movements into the Southern Hemisphere corresponded to increasing primary productivity. Our findings suggest that the Bobolink’s southbound migration is broadly constrained by resource availability, and its non-breeding distribution has been shaped by the seasonal phenology of grasslands in both time and space. This is the first documentation of individual birds from across a continental breeding range exhibiting phenological matching during their post-breeding southward migration. Known conservation threats overlap temporally and spatially with large concentrations of Bobolinks, and should be closely examined. We emphasize the need to consider how individuals move and interact with their environment throughout their annual cycle and over hemispheric scales.
Rowher, S. 2013. Molt intensity and conservation of a molt migrant (Passerina ciris) in northwest Mexico. Condor 115:421-433.
Abstract: I describe primary replacement in molt-migrant Painted Buntings (Passerina ciris) captured during molt in northern coastal Sinaloa. Primary replacement is rapid, start dates vary substantially by year, and, especially in females, start and end dates for the molt overlap broadly in some years. The earliest adult females to initiate primary replacement start at the same time as adult males, but many females initiate molt very late, apparently because their mates desert late broods to migrate and molt early. These issues conspire to make traditional estimates of the duration of primary replacement invalid; thus, I calculate molt duration as D = L/G, where L is the summed length of independently grown primary and G is the primaries’ growth rate. Adult females replace their primaries in 30.3 (SE = 4.27) days, adult males in 34.3 (SE = 2.99) days. For 54 hatch-year birds that were molting when captured I calculated start dates for the eccentric molt to show, for the first time for any species, that young birds that initiate this partial replacement of primaries later in the season replace fewer feathers. The intensity of the primary molt in adult females, the sexual conflict that results in many females initiating molt much later than males, and recent habitat changes in coastal northwest Mexico, all conspire to suggest that the cause of the decline in the Midwestern breeding population of the Painted Bunting is likely related to recent increases in the mortality of adult females during their annual post-breeding molt.
Rohwer, S., K.A. Hobson, and V.G. Rowher. 2009. Migratory double breeding in Neotropical migrants. Proceedings of the National Academy of Sciences, 106:19050-19055.
Abstract: Neotropical migratory songbirds typically breed in temperate regions and then travel long distances to spend the majority of the annual cycle in tropical wintering areas. Using stable-isotope methodology, we provide quantitative evidence of dual breeding ranges for 5 species of Neotropical migrants. Each is well known to have a Neotropical winter range and a breeding range in the United States and Canada. However, after their first bout of breeding in the north, many individuals migrate hundreds to thousands of kilometers south in midsummer to breed a second time during the same summer in coastal west Mexico or Baja California Sur. They then migrate further south to their final wintering areas in the Neotropics. Our discovery of dual breeding ranges in Neotropical migrants reveals a hitherto unrealized flexibility in life-history strategies for these species and underscores that demographic models and conservation plans must consider dual breeding for these migrants.
Rohwer, S., K.A. Hobson, and S. Yang. 2011. Stable isotopes (delta D) reveal east-west differences in scheduling of molt and migration in northern rough-winged swallows (Stelgidopteryx serripennis). Auk 128:522-530.
Abstract: We used stable-isotope (delta D) measurements of primary feathers to demonstrate that Northern Rough-winged Swallows (Stelgidopteryx serripennis) that breed in western North America migrate to the monsoon region of northwest Mexico for their annual postbreeding molt. Both adults and juveniles replace all their primaries in late summer. As expected, in samples of adults and fledglings collected at a northern breeding locality in eastern Washington, primary delta D values of adults were of southern origin, whereas those of fledglings, whose feathers were grown in the nest, were consistent with their northern origin. Similarly, some young birds collected as they were replacing primaries in northwest Mexico had a southern signature in newly replaced primaries but a northern signature in their yet unreplaced juvenile primaries, which indicates that they were molt migrants from the north. Feather delta D values increased from P1 to P9 in breeding adults collected in upstate New York. In the eastern United States, both adults and juveniles replace their primaries as they migrate southward in the fall. These isotopic results are consistent with the observation that Northern Rough-winged Swallows are halfway through their primary molt when they reach the Gulf Coast, where they pause in coastal marshes to finish the primary molt before crossing the Gulf of Mexico. The striking difference in molt and migration schedules between eastern and western populations of Northern Rough-winged Swallows suggests further investigations of their species status be conducted in the region where these populations make contact.
Rohwer, S., V.G. Rohwer, A.T. Peterson, A.G. Navarro-Siguenza, and P. English. 2012. Assessing migratory double breeding through complementary specimen densities and breeding records. Condor 114:1-14.
Abstract: We re-evaluate the plausibility that five species of birds that breed in late summer in northwestern Mexico are migratory double breeders that first bred earlier in the same season to the north. We use data aggregated from scientific collections to generate abundance indices that adjust counts of specimens in collections by collecting effort, which we measure as the number of passerines collected in the same region and time period as the species of interest. Our abundance indices generally show displaced phenologies, such that presumed double breeders arrive and breed early in the north, then later in northwestern Mexico. We also compare breeding records for these regions, but these records could not be corrected for effort. Our phenologies suggest that the breeding populations of the Yellow-billed Cuckoo (Coccyzus americanus) from the western U.S. and northwestern Mexico may be derived from birds that bred earlier in eastern North America. Similarly, Orchard Orioles (Icterus spurius) breeding in late summer in northwestern Mexico and on the Mexican plateau may be derived from birds that attempted to breed earlier in North America. Our abundance indices and other new data suggest migratory double breeding is less likely in the Hooded Oriole (I. cucullatus) and probably not occurring in the Yellow-breasted Chat (Icteria virens) and Cassin’s Vireo (Vireo cassinii).
Rohwer, S., and C.S. Wood. 2013. Abundant early-summer breeding in Sinaloa does not suggest post-migratino breeding in three potential double breeders. Wilson Journal of Ornithology 125:243-250.
Abstract: Rohwer et al. (2009) present isotopic evidence of migratory double breeding by five species of birds that were breeding in July and August in northwestern Mexico. The presence of old brood patches in these species, combined with their late breeding in Mexico, suggested that these species had bred earlier in the north. Here we present data showing that Orchard Orioles and Yellow-breasted Chats breed as commonly in coastal Sinaloa in late May and early June as they do later in the summer; further, many females of these species examined in early June 2011 had downy ventral apteria, indicating that they were breeding for the first time in their annual cycle in Sinaloa. Thus, the old brood patches observed in these species in July and August, when they are still breeding in northwestern Mexico, may reflect earlier breeding attempts by those same individuals in Mexico. Yellow-billed Cuckoos seldom call and are uncommon in northwestern Mexico until late June and likely do not begin breeding until July. For Yellow-billed Cuckoos there had been no description of how the ventral apterium changes with breeding, so Rohwer et al. (2009) assumed that it followed a passerine pattern of refeathering during the post-breeding molt. To test this assumption we examined the ventral apterium in cuckoo specimens collected throughout the winter and found that it remains featherless throughout the year, including immediately after the complete mid winter molt. Thus, the bare ventral apteria of cuckoos arriving in northwestern Mexico in June and July do not constitute evidence of prior breeding in that year.
Rohwer, S., Grason, E. and Navarro-Sigüenza, A.G. 2015. Irrigation and avifaunal change in coastal Northwest Mexico: has irrigated habit attracted threatened migratory species? PeerJ 3:e1187.
Abstract: Irrigation in desert ecosystems can either reduce or increase species diversity. Groundwater pumping often lowers water tables and reduces natural wetlands, whereas canal irrigation often creates mesic habitat, resulting in great increases in avian diversity from irrigation. Here we compare a dataset of potential natural vegetation to recent datasets from areal and satellite imagery to show that 60% of the land in the coastal plain of southern Sonora and northern Sinaloa lying below 200 m elevation has been converted by irrigation to more mesic habitats. We then use the record of bird specimens in the world's museums from this same region of Mexico to examine the avian community before and after the development of extensive irrigation. In general these museum records show an increase in the abundance and diversity of breeding birds associated with mesic habitats. Although thorn forest birds have likely decreased in total numbers, most are common enough in the remaining thorn forest that collection records did not indicate their probable decline. Four migrants having most of their breeding ranges in the US or Canada, Yellow-billed Cuckoo, Cliff Swallow, Bell's Vireo, and Orchard Oriole, apparently have increased dramatically as breeders in irrigated habitats of NW Mexico. Because these species have decreased or even largely disappeared as breeding birds in parts of the US or Canada, further research should assess whether their increases in new mesic habitats of NW Mexico are linked to their declines as breeding birds in Canada and the US For Bell's Vireo recent specimens from Sinaloa suggest its new breeding population in NW Mexico may be composed partly of the endangered Least Bell's Vireo.
Rohwer, S. and Rohwer, V.G. 2018. Breeding and multiple waves of primary molt in common ground doves of coastal Sinaloa. PeerJ 6:e4243.
Abstract: For adult Common Ground Doves from Sinaloa we demonstrate that the primaries are a single molt series, which sometimes feature two (in one case three) waves of feather replacement. Such stepwise primary replacement is found in many large birds but, at 40 g, this dove is much the smallest species reported to have multiple waves of replacement proceeding through its primaries simultaneously. Pre-breeding juvenile Common Ground Doves never feature two waves of primary replacement. Juveniles usually have more than two adjacent feathers growing simultaneously and replace their primaries in about 100 days. In contrast adults, which extensively overlap molt and breeding, usually grow just a single primary at a time, and require at least 145 days to replace their primaries. Molt arrests are thought to drive the generation of new waves of primary replacement in a diversity of large birds. For adult Common Ground Doves, we found molt arrests to be strongly associated with active crop glands, suggesting that the demands of parental care cause arrests in primary replacement in this dove. For those adults with two primary molt waves, initiation of an inner wave was most frequently observed once the outer wave had reached P10. Thus, unlike reports for large birds, Common Ground Doves usually suppress the initiation of a new wave of molt starting at P1 when the preceding wave arrests before reaching the distal primaries. This assures that relatively fresh inner primaries are not replaced redundantly, overcoming a serious flaw in stepwise molting in large birds (Rohwer, 1999).
Rohwer, V.G., Rohwer, S. and Wingfield, J.C. 2020. Despotic aggression in pre-moulting painted buntings. Royal Society Open Science 7:191510.
Abstract: Aggression in territorial social systems is easy to interpret because the benefits of territorial defence mostly accrue to the territorial holder. However, in non-territorial systems, high aggression seems puzzling and raises intriguing evolutionary questions. We describe extreme rates of despotism between age classes in a passerine bird, the painted bunting (Passerina ciris), during the pre-moulting period. Aggressive encounters were not associated with aggressors gaining immediate access to resources. Instead, conspecifics, and even other species, were pursued as though being harassed; this aggression generated an ideal despotic habitat distribution such that densities of adult males were higher in high-quality sites. Aggression was not a by-product of elevated testosterone carried over from the breeding season but, rather, appeared associated with dehydroepiandrosterone, a hormone that changes rates of aggression in non-breeding birds without generating the detrimental effects of high testosterone titres that control aggression in the breeding season. This extraordinary pre-moult aggression seems puzzling because individual buntings do not hold defined territories during their moult. We speculate that this high aggression evolved as a means of regulating the number of conspecifics that moulted in what were historically small habitat patches with limited food for supporting the extremely rapid moults of painted buntings.
Sadoti, G., Jones, A.L., Shriver, W.G. and Vickery, P.D. 2017. Employing landscape metrics in an open population model to estimate demographic parameters of a grassland bird. Landscape Ecology 32:1553-1562.
Abstract: Context The importance of landscape context is increasingly recognized when studying relationships between populations. Recent advances in open population modeling allow the employment of landscape metrics to estimate demographic parameters underlying population variation through time and space. Objectives Our primary objectives were to (1) describe the influence of landscape metrics on demographic parameters in the grasshopper sparrow (Ammodramus savannarum) and (2) quantify the contributions of these demographic parameters in influencing variation in territory counts through time. We anticipated results would allow us to make recommendations for prioritizing site conservation for this grass-land-obligate species of regional conservation concern. Methods We employed territory counts spanning 13 years from Massachusetts, USA in open population models to estimate the effects of landscape metrics, territory density, and site quality on three demographic parameters. Results The best model estimated highest initial numbers of territories in larger, more distant sites. Overall growth rates <1 were estimated during 1993-2005, while growth rates >1 were estimated in larger sites with a higher habitat quality index and low to medium relative density. Highest rates of annual immigration were estimated for larger sites. Growth rate explained the greatest proportion of variation in territory counts through time. Conclusions Open population models allowed us to identify the effects of landscape context on multiple grasshopper sparrow demographic parameters. We encourage further application of these and related models to grassland birds. Beyond maintaining grasslands in the region, we recommend the conservation of large, distant, and previously occupied sites to benefit regional populations.
Schmitt, C.J., Cook, J.A., Zamudio, K.R. and Edwards, S.V. 2019. Museum specimens of terrestrial vertebrates are sensitive indicators of environmental change in the Anthropocene. Philosophical Transactions of the Royal Society B 374:20170387.
Abstract: Natural history museums and the specimen collections they curate are vital scientific infrastructure, a fact as true today as it was when biologists began collecting and preserving specimens over 200 years ago. The importance of museum specimens in studies of taxonomy, systematics, ecology and evolutionary biology is evidenced by a rich and abundant literature, yet creative and novel uses of specimens are constantly broadening the impact of natural history collections on biodiversity science and global sustainability. Excellent examples of the critical importance of specimens come from their use in documenting the consequences of environmental change, which is particularly relevant considering the alarming rate at which we now modify our planet in the Anthropocene. In this review, we highlight the important role of bird, mammal and amphibian specimens in documenting the Anthropocene and provide examples that underscore the need for continued collection of museum specimens.
Silver, M., and C.R. Griffin. 2009. Nesting habitat characteristics of bank swallows and belted kingfishers on the Connecticut River. Northeastern Naturalist 16:519-534.
Abstract: Ceryle alcyon (Belted Kingfisher) and Riparia riparia (Bank Swallow) rely on vertical eroded banks for nesting. We inventoried Belted Kingfisher and Bank Swallow nesting banks along a 91.6-km section of the Connecticut River in Massachusetts, New Hampshire, and Vermont, including stretches where bank stabilization projects are completed, under construction, or planned. In the case of Bank Swallows, we also assessed the availability of potential nesting habitat in the study area. Forty-four Belted Kingfisher nesting sites and 12 Bank Swallow colonies were detected in the study area. Both species used banks with a low percentage of vegetative cover and a steep slope. Belted Kingfishers used high narrow banks. Bank Swallows used wide banks composed of well-drained, fine sandy loam soils. Potential Bank Swallow nesting sites were limited and in comparison to the sites actually used by Bank Swallows, they were narrower, more vegetated, and composed of more coarse soils. The impact of bank stabilization on Belted Kingfishers is probably minimal. However, bank stabilization eliminated three of twelve Bank Swallow colony sites that served as habitat for approximate to 20% of nesting pairs in the study area between 1999 and 2005.
Slay, C. M. and K. G. Smith. 2009. A comparison of nest success rates of four shrubland specialists in conservation managed fields to other managed and unmanaged shrublands. Pp. 705-712. In: T. Rich, C. Arizmendi, C. Thompson, and D. Demarest, eds. Tundra to Tropics: Birds, Habitats, and People. Proceedings of the Fourth International Partners in Flight Conference. Partners in Flight.
Abstract: Shrubland birds are disturbance dependent species and are experiencing population declines of 1–3%/year range wide. In our study, we determined nest success rates of four shrubland species, Blue-winged Warbler (Vermivora pinus), Prairie Warbler (Dendroica discolor), Indigo Bunting (Passerina cyanea), and Field Sparrow (Spizella pusilla), at Bent of the River Audubon Center, Southbury, Connecticut, USA. Field sites were conservation-managed fields that were actively managed for shrubland specialists. Data were collected on 123 nests (May–August, 2004–2006) and nest success rates (calculated using the Mayfield method) were 0.37 ± 0.003 for Blue-winged Warbler, 0.35 ± 0.013 for Prairie Warbler, 0.65 ± 0.009 for Indigo Bunting, and 0.50 ± 0.014 for Field Sparrow. Our study of these species is one of only three from the New England/ Mid-Atlantic Coast Region. We compiled data from studies from all regions reporting nest success of these species, conducted in a variety of managed and unmanaged shrublands. We compared our results to these studies and found nest success rates in conservation-managed fields to be similar to or higher than studies in different habitat management types in different regions. Based on our comparison of results from the limited number of studies on nest success rates of shrubland birds, the rotational mowing, selective tree removal, and invasive plant control regimes used to maintain conservation-managed shrublands are effective management practices to maintain high to moderate rates of nest success and may even be preferable to other management practices where shrubland species are targets for conservation.
Slay, C. M., K. S. Ellison, C. A. Ribic, K. G. Smith, and C. M. Schmitz. 2012. Nocturnal activity of nesting shrubland and grassland passerines. Pp. 105–116. In: C. A. Ribic, F. R. Thompson III, and P. J. Pietz, eds. Video Surveillance of Nesting Birds. Studies in Avian Biology no. 43.
Abstract: Nocturnal behaviors and sleep patterns of nesting passerines remain largely undocumented in the field and are important to understanding responses to environmental pressures such as predation. We used nocturnal video recordings to describe activity and quantify behaviors of females with nestlings of four shrub land bird species and three grassland bird species (n = 19 nests). Among the shrubland birds, Blue-winged Warbler (Vermivora pinus), Prairie Warbler (Setophaga discolor), and Indigo Bunting (Passerina cyanea) returned to the nest for the night at the same time, around sunset. Among the grassland birds, Eastern Meadowlark (Sturnella magna) returned the earliest before sunset and Grasshopper Sparrow (Ammodramus savannarum) returned the latest after sunset. All species exhibited "back sleep" with the bill tucked under scapular feathers, and individuals awoke frequently for vigils or "peeks" at their surroundings. Sleep of all species was disrupted by nestling activity. Average duration of sleep bouts varied from 6 min (Grasshopper Sparrow) to 28 min (Blue-winged Warbler; Field Sparrow (Spizella pusilla). Mean overnight duration on the nest varied from 6.4 hr (Field Sparrow) to 8.8 hr (Indigo Bunting). On average, adults woke in the morning (the last waking before departing the nest) 20-30 min before sunrise. The first absence from the nest in the morning was short for all species, and nestlings were fed within 12 min of a parent's departure. Our study highlights the need for further video research on sleep patterns of nesting birds in the field to better understand basic natural history, energetic cost-benefits of sleep, and behavioral adaptations to environmental pressures
Sly, N.D., A.K. Townsend, C.C. Rimmer, J.M. Townsend, C.C. Latta, and I.J. Lovette. 2010. Phylogeography and conservation of the endemic Hispaniolan Palm-Tanagers (Aves: Phaenicophilus). Conservation Genetics 11:2121-2129.
Abstract: The Gray-crowned Palm-Tanager (Phaenicophilus poliocephalus), sometimes considered conspecific with its more widespread congener P. palmarum, is restricted to Haiti's Tiburon Peninsula, a biodiversity hotspot threatened by extensive habitat loss. We used a multilocus phylogeographic approach to identify evolutionarily distinct populations of Phaenicophilus. Mitochondrial haplotypes formed two reciprocally monophyletic groups separated by 5% uncorrected divergence. Genealogical patterns of differentiation at nuclear intron alleles were congruent with those of mtDNA, and the two species also differed in body size and shape. An ancient sea channel between the Tiburon Peninsula and mainland Haiti was likely a dispersal barrier that led to allopatric divergence, a hypothesis supported by our estimates of divergence times. Our results support the recognition of two Palm-Tanager species, confirming P. poliocephalus as Haiti's only endemic bird species and underscoring the need to protect the Tiburon Peninsula's single primary forest reserve.
Sly, N.D., A.K. Townsend, C.C. Rimmer, J.M. Townsend, C.C. Latta, and I.J. Lovette. 2011. Ancient islands and modern invasions: disparate phylogeographic histories among Hispaniola’s endemic birds. Molecular Ecology 20:5012-5024.
Abstract: With its large size, complex topography and high number of avian endemics, Hispaniola appears to be a likely candidate for the in situ speciation of its avifauna, despite the worldwide rarity of avian speciation within single islands. We used multilocus comparative phylogeography techniques to examine the pattern and history of divergence in 11 endemic birds representing potential within-island speciation events. Haplotype and allele networks from mitochondrial ND2 and nuclear intron loci reveal a consistent pattern: phylogeographic divergence within or between closely related species is correlated with the likely distribution of ancient sea barriers that once divided Hispaniola into several smaller paleo-islands. Coalescent and mitochondrial clock dating of divergences indicate species-specific response to different geological events over the wide span of the islands history. We found no evidence that ecological or topographical complexity generated diversity, either by creating open niches or by restricting long-term gene flow. Thus, no true within-island speciation appears to have occurred among the species sampled on Hispaniola. Divergence events predating the merging of Hispaniolas paleo-island blocks cannot be considered in situ divergence, and postmerging divergence in response to episodic island segmentation by marine flooding probably represents in situ vicariance or interarchipelago speciation by dispersal. Our work highlights the necessity of considering island geologic history while investigating the speciationarea relationship in birds and other taxa.
Studds, C.E., K.P. McFarland, Y. Aubry, C.C. Rimmer, K.A. Hobson, P.P. Marra, and L.I. Wassenaar. 2012. Stable-hydrogen isotope measures of natal dispersal reflect observed population declines in a threatened songbird. Diversity and Distributions 18:919-930.
Abstract: Measuring dispersal is crucial for estimating demographic rates that inform conservation plans for rare and threatened species. We evaluated natal dispersal patterns in Bicknell's thrush (Catharus bicknelli) across most of the breeding range using a 10-year data set of stable-hydrogen isotope ratios in feathers (d2HF) grown on the natal area and sampled 1 year later at the first breeding site. North-eastern United States and south-eastern Canada. We used d2HF values of adult thrushes sampled at 25 breeding sites as prior information for assigning first-time breeders to their natal site. We calculated the minimum distance birds moved from their natal to first breeding site and fit these data to three statistical distributions for characterizing the importance of long-distance dispersal: the exponential, Weibull and half-Cauchy. Finally, we assessed differences in the probability of dispersal across the breeding range and through time to understand spatio-temporal variation in demographic connectivity. The d2HF values of first-time breeders were lower compared with those of adults, a difference that was greater at the southern compared with northern breeding range extreme. Assignment tests accounting for age differences in d2HF suggested that most birds dispersed < 200 km from their natal area and within the centre of the breeding range, whereas comparatively few individuals dispersed up to 700 km. A Weibull distribution provided the best fit to these data. Two of three corrections for age differences in d2HF indicated that natal dispersal probability declined by 3038% from 1996 to 2005. Our findings suggest that estimating natal dispersal with d2HF measurements may contribute to understanding the resilience of geographically isolated Bicknell's thrush populations. Declining natal dispersal may be symptomatic of observed population declines and could compound this trend by limiting demographic exchange between habitat patches predicted to be increasingly isolated by natural and anthropogenic habitat changes.
Tavernia, B. G., and J. M. Reed. 2009. Spatial extent and habitat context influence the nature and strength of relationships between urbanization measures. Landscape and Urban Planning 92:47-52.
Abstract: A wide variety of metrics is used to quantify features of urbanization in ecological studies. Selecting statistically independent measures of urbanization depends upon the nature (multivariate collinearity) and strength (correlation coefficient) of correlations between urban metrics.We evaluated the influence of landscape extent and habitat context, factors that commonly differ between studies, on correlations between urban metrics. We examined the nature and strength of relationships between urban metrics at 1105 sites within Massachusetts, USA, including: population, agriculture cover, forest cover, wetland cover, dense residential cover, impervious surface cover, road length and greenspace cover. At each site, values were measured at five extents: 100m, 250 m, 500m, 1 km, and 2 km radii buffers. We also investigated the influence of habitat context on correlations by measuring values with a 1km radius buffer for 100 sites within each of three habitat contexts (salt marsh, forest, and freshwater marsh). Principal component analysis showed that spatial scale did not affect the nature of relationships, but habitat context did. The average strength of bivariate correlations significantly increased at larger extents, and was significantly lower in salt marsh habitat context. Our results indicate that no single set of urbanization metrics is universally applicable and underline the importance of using a suite of statistical techniques to characterize independent aspects of urban environments.
Tavernia, B. G., and J. M. Reed. 2010. Spatial, temporal, and life history assumptions influence consistency of landscape effects on species distributions. Landscape Ecology 25:1085-1097.
Abstract: Models describing relationships between landscape features and species distribution patterns often display inter-study inconsistencies. Identifying factors contributing to these inconsistencies is a vital step in clarifying the ecological importance of landscape features and synthesizing an effective knowledge base for use in conservation contexts. We examined the influence of several spatial, temporal, and life history assumptions on the outcomes of distribution versus landscape models (DLMs) relating wetland bird communities at 29 Massachusetts (USA) sites to independent urbanization, wetland, forest, and agricultural landscape gradients. We considered a bird specialization index as well as obligate and facultative species richness as response variables. Landscape gradients were quantified at 10 landscape extents (0–1000 m in 100 m increments) and three time periods (1971, 1985, 2005). Univariate models indicated that our specialization index showed: (1) the strongest response to landscape gradients at small extents (200 m); (2) a negative, threshold response to urbanization was superior to a linear fit; and (3) no evidence of time-lagged effects of landscape change. Interestingly, the form of our model (i.e. linear versus threshold) influenced the extent at which strongest effects were detected. Multivariate models relating the specialization index as well as obligate and facultative species richness to landscape gradients showed evidence of annual variability (i.e. composition, parameter estimates, and variability explained) that did not depend upon an organism’s degree of specialization. Our results provide evidence that violations of common assumptions (e.g. selection of appropriate extent, lack of time-lagged effects, etc.) can impact the outcome of DLMs, which could lead to inter-study inconsistencies.
Tavernia, B. G., and J. M. Reed. 2012. The impact of purple loosestrife (Lythrum salicaria) on wetland bird distributions. American Midland Naturalist 168:352-363.
Abstract: The exotic invasive wetland plant purple loosestrife (Lythrum salicaria) is often considered to have negative impacts on native plant and animal species, but this is debated. Clarifying its influence would provide insight into appropriate management actions following invasion. We investigated the influence of L. salicaria cover and density on abundances of wetland bird species that are associated with a variety of vegetation structures. We found evidence of relationships between L. salicaria measures and abundance for most species we examined, but these relationships did not always agree with our predictions based on species’ habitat associations. Some bird species positively responded whereas others negatively responded to increasing L. salicaria cover or density. Response curves varied in complexity and included linear and quadratic relationships as well as interactions. Our results suggested that L. salicaria did not categorically decrease habitat quality for all wetland bird species, and it may have had a positive influence on quality for some species. This ambiguity is not unique to L. salicaria invasion but applies to many changing habitat features. Therefore, there is likely no single appropriate strategy for managing L. salicaria when the goal is to maintain a diverse avian community in which species have divergent habitat preferences.
Thorne, L.H., Fuirst, M., Veit, R. and Baumann, Z. 2021. Mercury concentrations provide an indicator of marine foraging in coastal birds. Ecological Indicators 121:106922.
Abstract: The transfer of nutrients between marine and terrestrial systems has important ecological consequences, and animal movement is an important driver of nutrient transfer. Coastal birds forage in marine environments and breed in terrestrial habitats, and thus serve as vectors moving nutrients from the sea to the land. However, urbanization can influence the extent to which coastal birds forage in marine or terrestrial environments due to the availability of human subsidies. Establishing a reliable and straightforward indicator of marine foraging would be useful for assessing changes in the use of terrestrial vs. marine habitats in the face of urbanization and broader environmental change, and for understanding the flow of nutrients and energy between terrestrial and marine environments. Mercury (Hg) is a highly toxic heavy metal which bioaccumulates in marine food webs, and is a potential indicator of marine foraging. Methylmercury (MeHg), is present only in aquatic ecosystems and reaches elevated concentrations in the prey species of marine birds. Thus, high concentrations of MeHg would be expected for birds foraging in marine environments in comparison to those foraging on terrestrial sources. We hypothesized that the degree of marine foraging influences Hg uptake in coastal birds. To test this hypothesis, we combined GPS tracking data with measurements of Hg concentrations in the blood of herring gulls (Larus argentatus) along an urban gradient in the northeast United States. We examined Hg concentrations for 51 individual herring gulls tracked with GPS tags at study sites representing high, medium and low degrees of urbanization. Our results showed a strong and significant positive relationship between Hg concentrations and the proportion of herring gull foraging locations occurring in offshore waters. Hg concentrations differed significantly between herring gulls whose primary foraging habitat occurred in marine vs. terrestrial environments. Gulls in more urban colonies spent less time foraging in marine environments, and had significantly lower Hg concentrations than those at the more remote study. Our results suggest that Hg concentrations in blood can be used to reflect the extent of marine foraging for animals using both marine and terrestrial habitats. Hg concentrations could be valuable monitoring tool to assess how the use of marine foraging habitats changes through time (dietary shifts) or relative to environmental change such as urbanization.
Townsend, J.M., C.C. Rimmer, A.K. Townsend, and K.P. McFarland. 2011. Sex and age ratios of Bicknell's thrush wintering in Hispaniola. Wilson Journal of Ornithology 123:367-372.
Abstract: We investigated sex and age ratios of wintering Bicknell's Thrush (Catharus bicknelli) across a geographic gradient of sites on Hispaniola. The island-wide proportion male was 0.64 (n = 127), which is comparable to the known male bias in breeding areas. The proportion male varied geographically on Hispaniola, suggesting some level of habitat segregation. Male-biased ratios occurred at two sites whereas sex ratios at five sites did not differ from parity. The island-wide proportion adult was 0.72 and age ratios were significantly adult-biased at two sites. We assessed vegetative structure at all sites and the proportion of male thrushes increased significantly with density of understory vegetation. Age ratios were not associated with vegetation characteristics. Neither sex nor age ratios varied significantly with elevation. Our data suggest the possibility of sexual habitat segregation with males preferentially occupying cloud forest sites characterized by a thick understory of vines and saplings occurring at densities >10,000 stems/ha.
Trull, P.F., Finnegan, S. and Gallagher, A.J. 2018. A new method for catching Wilson's Storm Petrels Oceanites oceanicus at sea. Marine Ornithology 46:125-127.
Abstract: Catching oceanic birds is challenging for researchers interested in studying migration and feeding dynamics. To address that challenge, we evaluated a new method for catching Wilson's Storm Petrels Oceanites oceanicus at sea. Using an extended butterfly net and a sweeping technique, we successfully captured 50 sub-adult and adult storm petrels offshore in the Northwest Atlantic with a 94% success rate. All were processed without sign of physical trauma or injury; 100% flew off in apparently good condition. This method provides a cost-effective and safe approach for the capture and study of small oceanic birds attracted to fish slicks.
van Rees, C.B., Chang, P.R., Cosgrove, J., DesRochers, D.W., Gee, H.K., Gutscher-Chutz, J.L., Nadig, A., Nagata, S.E., Silbernagle, M., Underwood, J.G. and Uyehara, K. 2018. Estimation of vital rates for the Hawaiian gallinule, a cryptic, endangered waterbird. Journal of Fish and Wildlife Management 9:117-131.
Abstract: Vital rates describe the demographic traits of organisms and are an essential resource for wildlife managers to assess local resource conditions and to set objectives for and evaluate management actions. Endangered waterbirds on the Hawaiian Islands have been managed intensively at state and federal refuges since the 1970s, but with little quantitative research on their life history. Information on the vital rates of these taxa is needed to assess the efficacy of different management strategies and to target parts of the life cycle that may be limiting their recovery. Here, we present the most comprehensive data to date on the vital rates (reproduction and survival) of the Hawaiian gallinule Gallinula galeata sandvicensis, a behaviorally cryptic, endangered subspecies of wetland bird endemic to the Hawaiian Islands that is now found only on Kaua'i and O'ahu. We review unpublished reproduction data for 252 nests observed between 1979 and 2014 and assess a database of 1,620 sightings of 423 individually color-banded birds between 2004 and 2017. From the resighting data, we estimated annual apparent survival at two managed wetlands on O'ahu using Cormack-Jolly-Seber models in program MARK. We found that Hawaiian gallinules have smaller mean clutch sizes than do other species in the genus Gallinula and that clutch sizes on Kaua'i are larger than those on O'ahu. The longest-lived bird in our dataset was recovered dead at age 7 y and 8 mo, and the youngest confirmed age at first breeding was 1 y and 11 mo. In 4 y of monitoring 14 wetland sites, we confirmed three interwetland movements on O'ahu. In our pooled dataset, we found no statistically significant differences between managed and unmanaged wetlands in clutch size or reproductive success, but we acknowledge that there were limited data from unmanaged wetlands. Our best supported survival models estimated an overall annual apparent survival of 0.663 (95% CI = 0.5720.759); detection varied across wetlands and study years. First-year survival is a key missing component in our understanding of the demography of Hawaiian gallinules. These data provide the foundation for quantitative management and assessment of extinction risk of this endangered subspecies.
van Rees, C.B., Muñoz, M.A., Cooke, S.C. and Reed, J.M. 2021. Morphological Differences in the Island-Endemic Hawaiian Subspecies of the Common Gallinule Gallinula galeata. Pacific Science 74:345-364.
Abstract: The study of island subspecies provides excellent "natural experiments" for examining the impacts of different selective regimes on animal taxa. We examined the morphological differences between the Hawaiian and continental North American subspecies of the Common Gallinule (Gallinula galeata sandvicensis and G. g. cachinnans, respectively), for which the existing literature is both scant and contradictory. More than 200 live gallinules and >100 museum specimens were measured, and a meta-analysis of literature values on North American Common Gallinules was conducted to quantitatively assess differences in wing chord, culmen and tarsus length, and body mass between these subspecies. Hawaiian Common Gallinules had smaller wing chords (-2.5 to -4.0%), larger culmen (+4.5 to +7.0%) and tarsi (+5.5 to +23.0%), and slightly larger body masses (similar to+4.0%) than their mainland conspecifics. This is likely due to several factors including reduced predation pressure, shorter dispersal distances, nonmigratory behavior, and sedentary lifestyles associated with ecological differences between the Hawaiian Islands and the North American mainland. We also introduce the novel hypothesis that intra- and interspecific agonistic interactions due to habitat limitation are an additional selective force in driving these morphological changes.
van Rees, C.B. and Reed, J.M. 2018. Predicted effects of landscape change, sea level rise, and habitat management on the extirpation risk of the Hawaiian common gallinule (Gallinula galeata sandvicensis) on the island of O ‘ahu. PeerJ 6:e4990.
Abstract: We conducted a spatially explicit, stochastic, individually based population viability analysis for the Hawaiian common gallinule (Gallinula galeata sandvicensis), an endangered subspecies of waterbird endemic to fragmented coastal wetlands in Hawai'i. This subspecies persists on two islands, with no apparent movement between them. We assessed extirpation risk for birds on O'ahu, where the resident gallinule population is made up of several fragmented subpopulations. Data on genetic differentiation were used to delineate subpopulations and estimate dispersal rates between them. We used sensitivity analyses to gauge the impact of current uncertainty of vital rate parameters on population projections, to ascertain the relative importance of gallinule vital rates to population persistence, and to compare the efficacy of potential management strategies. We used available sea level rise projections to examine the relative vulnerability of O'ahu's gallinule population to habitat loss arising from this threat. Our model predicted persistence of the island's gallinule population at 160 years (similar to 40 generations), but with high probabilities of extirpation for small subpopulations. Sensitivity analyses highlighted the importance of juvenile and adult mortality to population persistence in Hawaiian gallinules, justifying current predator control efforts and suggesting the need for additional research on chick and fledgling survival. Subpopulation connectivity from dispersal had little effect on the persistence of the island-wide population, but strong effects on the persistence of smaller subpopulations. Our model also predicted island-wide population persistence under predicted sea level rise scenarios, but with O'ahu's largest gallinule populations losing >40% of current carrying capacity.
van Rees, C.B., Reed, J.M., Wilson, R.E., Underwood, J.G. and Sonsthagen, S.A. 2018. Small-scale genetic structure in an endangered wetland specialist: possible effects of landscape change and population recovery. Conservation Genetics 19:129-142.
Abstract: The effects of anthropogenic landscape change on genetic population structure are well studied, but the temporal and spatial scales at which genetic structure can develop, especially in taxa with high dispersal capabilities like birds, are less well understood. We investigated population structure in the Hawaiian gallinule (Gallinula galeata sandvicensis), an endangered wetland specialist bird on the island of O`ahu (Hawai`i, USA). Hawaiian gallinules have experienced a gradual population recovery from near extinction in the 1950s, and have recolonized wetlands on O`ahu in the context of a rapidly urbanizing landscape. We genotyped 152 Hawaiian gallinules at 12 microsatellite loci and sequenced a 520 base-pair fragment of the ND2 region of mitochondrial DNA (mtDNA) from individuals captured at 13 wetland locations on O`ahu in 2014-2016. We observed moderate to high genetic structuring (overall microsatellite F-ST = 0.098, mtDNA F-ST = 0.248) among populations of Hawaiian gallinules occupying wetlands at very close geographic proximity (e.g., 1.5-55 km). Asymmetry in gene flow estimates suggests that Hawaiian gallinules may have persisted in 2-3 strongholds which served as source populations that recolonized more recently restored habitats currently supporting large numbers of birds. Our results highlight that genetic structure can develop in taxa that are expanding their range after severe population decline, and that biologically significant structuring can occur over small geographic distances, even in avian taxa.
van Rees, C.B., Reed, J.M., Wilson, R.E., Underwood, J.G. and Sonsthagen, S.A. 2018. Landscape genetics identifies streams and drainage infrastructure as dispersal corridors for an endangered wetland bird. Ecology and Evolution 8:8328-8343.
Abstract: Anthropogenic alterations to landscape structure and composition can have significant impacts on biodiversity, potentially leading to species extinctions. Population-level impacts of landscape change are mediated by animal behaviors, in particular dispersal behavior. Little is known about the dispersal habits of rails (Rallidae) due to their cryptic behavior and tendency to occupy densely vegetated habitats. The effects of landscape structure on the movement behavior of waterbirds in general are poorly studied due to their reputation for having high dispersal abilities. We used a landscape genetic approach to test hypotheses of landscape effects on dispersal behavior of the Hawaiian gallinule (Gallinula galeata sandvicensis), an endangered subspecies endemic to the Hawaiian Islands. We created a suite of alternative resistance surfaces representing biologically plausible a priori hypotheses of how gallinules might navigate the landscape matrix and ranked these surfaces by their ability to explain observed patterns in genetic distance among 12 populations on the island of O`ahu. We modeled effective distance among wetland locations on all surfaces using both cumulative least-cost-path and resistance-distance approaches and evaluated relative model performance using Mantel tests, a causal modeling approach, and the mixed-model maximum-likelihood population-effects framework. Across all genetic markers, simulation methods, and model comparison metrics, surfaces that treated linear water features like streams, ditches, and canals as corridors for gallinule movement outperformed all other models. This is the first landscape genetic study on the movement behavior of any waterbird species to our knowledge. Our results indicate that lotic water features, including drainage infrastructure previously thought to be of minimal habitat value, contribute to habitat connectivity in this listed subspecies.
Watson, M.J., J.A. Spendelow, and J.J. Hatch. 2012. Post-fledging brood and care division in the roseate tern (Sterna dougallii). Journal of Ethology 30:29-34.
Abstract: Extended post-fledging parental care is an important aspect of parental care in birds, although little studied due to logistic difficulties. Commonly, the brood is split physically (brood division) and/or preferential care is given to a subset of the brood by one parent or the other (care division). Among gulls and tern (Laridae), males and females generally share parental activities during the pre-fledging period, but the allocation of parental care after fledging is little documented. This study examined the behaviour of male and female roseate terns (Sterna dougallii) during the late chick-rearing and early post-fledging periods, and in particular the amount of feeds and the time spent in attendance given to individual chicks/fledglings. Pre-fledging parental care was biparental in all cases. Post-fledging parental care was dependent on the number of fledglings in the brood. Males and females continued biparental care in clutches with one surviving fledgling, while in two-fledgling clutches, males fed the A-fledgling while females fed the B-fledgling. Overall, there was no difference in attendance, only in feeds. This division of care may be influenced by the male only being certain of the paternity of the A-chick but not by chick sex.