Variation in nest characteristics and brooding patterns of female Black-throated Blue Warblers is associated with thermal cues

ABSTRACT Thermal variation poses a problem for nesting birds and can result in reduced offspring growth rates and survival. To increase the thermal stability of the nest, females can adjust nest characteristics and nest attendance in response to changes in environmental conditions. However, it is unclear how and to what extent females modify parental behaviors during various stages of offspring development. We tested the hypothesis that females adjust nest characteristics and brooding patterns in response to thermal variation during the nest-building and nestling stages, respectively. We examined elevational variation in nest location, nest construction, and brooding patterns in the migratory Black-throated Blue Warbler (Setophaga caerulescens) across a 2°C gradient at the Hubbard Brook Experimental Forest, New Hampshire, USA. Density of woody stems at nest sites and nest wall thickness increased from low to high elevation, corresponding to decreasing temperatures, but we found no relationship between wea...