Nest Success and Nesting Habits of Eastern Kingbirds and Other Flycatchers

Abstract

Patterns of nest placement and its relationship to nest success in the Eastern Kingbird (Tyrannus tyrannus) were studied in populations breeding in New York and Kansas. Data were augmented with information on nest placement in other open-nesting tyrannids in order to examine the hypothesis that these flycatchers place their nests chiefly so as to conceal them from predators. Nesting success was significantly greater in New York than in Kansas but was relatively high in both populations, as is apparently true of North American breeding flycatchers in general. Geographic variation in nest placement in the Eastern Kingbird was relatively small and statistical comparisons of failed and successful nests indicated that nests placed at mid-heights in the tree, and about midway between the center of the tree and canopy edge, were most successful. These nest sites were also the most commonly used sites. Increased vegetative cover around the nest and a greater number of supporting branches for the nest were also associated with success, and it is their interaction with nest height and distance from the canopy edge that is apparently most important in determining success. Most tyrant flycatchers nest several meters or more above the ground, and interspecific variation in nest placement matches the range of sites used by Eastern Kingbirds. Aggressive nest defense is apparently characteristic of the family, and average nest height is also positively correlated with length of the nestling period. These facts support the predator-avoidance hypothesis and suggest that nest placement habits and aggressive nest defense are means by which open-nesting birds can reduce rates of nestling mortality.