Nest Defense Behavior of Suburban and Rural Red-shouldered Hawks

Abstract

Urban and suburban raptors live in close proximity to humans, and some species defend their nests and young vigorously, even diving at or striking humans walking on the ground. Such raptors may be more defensive of their nests than rural birds. We investigated (1) whether Red-shouldered Hawk (Buteo lineatus) nest defense behavior differs between suburban and rural birds, (2) whether any environmental conditions are associated with aggressive nest defense, and (3) whether nest defense behavior is associated with reproductive rate. First, we used an experimental walk-up protocol to approach nests with incubating or brooding Red-shouldered Hawks at suburban and rural sites, and we scored the hawk's response to our approach. We measured environmental variables (nest height, distance to the nearest road and nearest house, and habitat proportions within 500 m of the nest) and determined reproductive rate. Second, we used our historical database to retrospectively classify hawks as most aggressive, moderately aggressive, or not aggressive, and we measured the same environmental variables at their nest sites. We found that most birds at both suburban and rural study areas responded to our experimental approach with minimal nest defense, though suburban birds responded with higher levels of nest defense. Environmental variables were unrelated to nest defense intensity in the experimental study. For the retrospective study in the suburban area, nest height was the only environmental factor distinguishing aggressive hawks from non-aggressive ones; aggressive nest defensive behavior was associated with lower nests. Reproductive rate was unrelated to nest defense behavior in both studies. Knowing which environmental factors may contribute to more aggressive behavior may help researchers, managers, and residents better understand bird behavior and predict the circumstances under which problems might develop, particularly in urban/suburban environments.