The Cost of Incubation: Manipulating Nest Microclimate and Examining Nest Site Selection to Understand Energetic Tradeoffs during Incubation in Wood Ducks (Aix sponsa)

Abstract

Incubating Wood Ducks (Aix sponsa), face tradeoffs between time spent incubating with time spent foraging. To explore the costs and investment strategies of incubating female wood ducks I (a) manipulated the microclimate of nests by reducing down insulation from 4.0 g to 0.5 g, and (b) examined the relationship between nest-site microclimate with nest site selection. Females with reduced down faced increased cooling rats, and therefore shortened morning recesses and increased daily incubation constancy. Behavioral changes occurred progressively through the incubation period and were not influenced by female body mass. Overall clutch temperatures did not differ between treatments and correspondingly, there were no differences in length of the incubation period, hatching success, or ducking phenotypes. I detected a novel level of plasticity in daily incubation behaviors of female wood ducks in response to variations in clutch cooling rates and ambient temperatures. Nest site selection was positively associated with higher early season nest-box temperature variability. Further, warmer nest-boxes were initiated earlier in the early-breeding season and were less likely to be abandoned. Females who had previously experience in nest-boxes selected nest-boxes that were cooler than available nearby boxes, where new females or females without previous experience in selected nest-boxes selected boxes randomly without relation to nest-box microclimate. In this study, I found evidence of female wood ducks making investment decisions, both in changing incubation behaviors and selecting for warm nesting boxes, in order to balance energy between conflicting needs between them and their offspring.