Sitting in the open: how nest microclimate influences incubation behavior in an open-cup nesting passerine

Abstract

Incubating passerines modulate their behavior in response to local conditions and changing energetic demands, and nest microclimate can significantly influence female incubation behavior. We tested how ambient temperature affects incubation behavior, and how incubation behavior in turn influences in-nest temperature for an open-cup nesting passerine, the hooded warbler Setophaga citrina. We also examined how covariates of brown-headed cowbird Molothrus ater parasitism, clutch size, year, and females' experience influence female management of incubation behavior and in-nest temperatures. We used iButtons to measure nest microclimate and in-nest temperatures for incubating hooded warblers in southern Ohio, USA, and we used in-nest temperatures to estimate incubation behavior. Under warmer ambient conditions, females incubated for longer periods of time, with fewer (but longer) off-bouts, resulting in a higher proportion of time spent incubating. These data suggested that females under cooler circumstances leave the nest more to forage for themselves; while warmer conditions allowed females to stay on the nest longer for each on-bout, and for a greater proportion of the day. However, increasing variability of ambient temperatures caused females to take more off-bouts and on-bouts. Incubation behaviors directly influenced the realized in-nest temperatures: longer on-bouts and more incubation time overall generated higher and more stable in-nest temperatures. In contrast, longer off-bouts resulted in lower mean in-nest temperatures and less stable nest temperatures, resulting in lower hatching success. Our results linked the flexibility of incubation behavior in response to nest microclimate variation to in-nest temperatures and hatching success for an open-cup nesting species, contributing to a better understanding of how climate influences critical maternal behaviors.

Keywords: climate, incubation behavior, nest microclimate, parent–offspring conflict, reproductive rate, tradeoff