Cerulean Warbler Territory Size is Influenced by Prey-Rich Tree Abundance

Abstract

Food availability has far-reaching implications for the breeding success of birds and may be
a limiting resource affecting populations. Many birds, such as the Cerulean Warbler (Setophaga cerulea),
defend territories for foraging purposes, and the size of their territory is likely to vary with an area’s
potential for foraging. This study investigated the abundance of prey in various trees (white oak group
[Quercus alba L. and Q. prinus L.], hickories [Carya spp.], and sugar maples [Acer saccharum Marshall]) to
understand the relationship between prey availability, tree species, and territory size. Relative prey
abundance using caterpillar frass (droppings) was calculated. Estimated basal area of the various tree groups
within each territory was used to determine whether Cerulean Warbler territory size is predicted by prey-rich
trees. The white oak group and hickory group dropped almost double the amount of frass compared to
sugar maples, suggesting that the former groups may provide more prey to foraging Cerulean Warblers.
Territory size (n = 51) was negatively correlated with the basal area of trees in the white oak group,
positively correlated to the basal area of the sugar maple group, yet no relationship to hickory or total tree
basal area (combined tree types) was found. Therefore, Cerulean Warblers may adjust territory size based on
an awareness of the prey-productivity of different tree taxa.