Comparative analysis of habitat selection, nest site and nest success by cedar waxwings (Bombycilla cedrorum) and eastern kingbirds (Tyrannus tyrannus)

We compared nest success, habitat use and nest site selection of cedar waxwings (Bombycilla cedrorum) and eastern kingbirds (Tyrannus tyrannus) breeding in the same locations over a 3-yr period to determine if nest success differed between species, or with habitat or nest sites. Nest success was lower in waxwings in all 3 yr (3-yr average: 18% vs. 55%). Both species preferred hawthorns (Crataegus) as nest trees, but in neither species was nest success higher when nests were placed in hawthorns. Nest success did, however, vary with habitat structure: successful kingbirds nests were usually located in the most open habitat (i.e., lowest canopy cover and surrounded by the fewest trees), whereas failed waxwing nests were located in habitats with the densest vegetation. Habitats of failed kingbird and successful waxwing nests were intermediate and similar. Nest sites were very similar, except that waxwing nests were much more concealed in the nest tree's vegetation. However neither cover nor other nest site variables differed between failed and successful nests within either species. A discriminant function analysis that used mainly habitat variables correctly classified 68% of failed waxwing and 64% of successful kingbird nests, but less than 50% of failed kingbird and successful waxwing nests. Thus, kingbirds and waxwings overlap extensively in habitat use and nest sites, but kingbirds prefer more open habitats, presumably because it allows them to detect predators and defend their nests. Waxwings prefer habitats with denser vegetation, presumably because they rely upon inconspicuous behavior to avoid nest predators. Failed kingbird nests were in waxwing-like habitats, suggesting a link between nest sites, habitats and parental behavior. We believe that the characteristic aggressive nest defense of kingbirds was the major reason for their higher nesting success.