Avian foliage structure preferences for foraging and the effect of prey biomass

Abstract

Aviary experiments using artificial foliage were conducted on two paruline warblers, black-throated blue warblers, Dendroica caerulescens, and black-throated green warblers, D. virens, to determine whether these bird species display foliage structure preferences when prey biomass is equal on each foliage structure, whether their preferences are consistent and transitive, and whether increasing prey biomass can reverse their preferences. Most black-throated blue warblers displayed preferences for structures simulating sugar maple, Acer saccharum, foliage at the distal region of the branch (short sugar maple) over structures simulating yellow birch, Betula alleghaniensis, foliage (artificial yellow birch) and over structures simulating sugar maple foliage on the region of the branch more proximal to the trunk (long sugar maple). The artificial yellow birch foliage was generally preferred over the long sugar maple. Most black-throated green warblers displayed no preference between short sugar maple and yellow birch, but preferred both of these over long sugar maple. In all cases, preferences were consistent and transitive, and increasing prey biomass reversed the preference. However, the increase in prey biomass needed to reverse the preferences of black-throated green warblers was greater than for black-throated blue warblers. These structure preferences may be based on considerations of the costs and benefits of foraging on the different foliage types.