We are studying habitat selection by grassland birds. Specifically, we are addressing the question of why there are fewer grassland birds per unit area present on small fields relative to large fields. Understanding the mechanism of this process is important for conservation, as it will either underscore the importance of preserving large fields or provide a means of managing small fields to be more suitable for grassland birds. We have been examining this question in Bobolinks, and have tested hypotheses relating to two specific mechanisms: 1. that Bobolinks select fields based on how open they are, rather than how large they are, and 2. That animals perceive a greater risk due to avian predators on small fields relative to large fields.