Geographic variation in incubation behavior of a widely distributed passerine bird

Abstract

Incubating birds must trade-off leaving the nest to forage with staying on the nest to maintain optimal temperatures for developing embryos. This trade-off is expressed through incubation behavior, which can be heavily influenced by climate, food availability, attentiveness of their mates, and nest predation risk. Comparative studies across species have shown that incubation behavior varies across latitude, but few studies have explored how incubation behavior varies across sites within species. We might expect incubation behavior to be flexible and respond to local environmental challenges; alternatively, behavior may be relatively fixed and vary little across a species' range. We explored four incubation behaviors (male feeding rate, female off-bout duration, female off-bout frequency, and the proportion of time incubating females spent on the nest) in a widespread songbird, the yellow warbler (Setophaga petechia), breeding at a temperate and subarctic site. As temperatures warmed at both sites, males fed females less often, and as male feeding rates decreased, off-bout durations and frequencies increased causing the proportion of time on the nest to decrease. While incubation behaviors changed in similar ways between sites, off-bout durations shortened with increasing male feeding rates most strongly at the temperate site. Overall, these results show flexibility in incubation behaviors in response to different environmental cues, which likely minimize costs associated with provisioning incubating parents and maintaining warm nest temperatures, and suggests that male feeding may be especially important for breeding in cold regions.

Fig 1. Yellow warbler incubation behavior at a subarctic and temperate site.

Variation in incubation behavior when correlated with significant predictor variables of minimum temperature and male feeding rate. Slopes did not differ between subarctic and temperate sites for three behaviors (male feeding rate, proportion of time on the nest, and off-bout frequency) but are plotted to illustrate patterns with minimum temperature and male feeding rates. Slopes between subarctic and temperate females were significantly different for off-bout duration (p = 0.04). Sample sizes for all behaviors were: subarctic: n = 30; temperate n = 16.