Nest site microclimate and the cost of incubation in Orange-crowned Warblers

PELUC, S. I.; SILLETT, T. S.; ROTENBERRY J.

Santa Barbara, CA

Congreso; 123rd Meeting of the American Ornithologists' Union; 2005

Appropriate nest temperature and humidity are essential during incubation to ensure successful egg hatching. Ideally, incubating parents should fully provide these microclimate elements either through selection of optimal nests sites and incubating behavior. Nests on different vegetation strata are exposed to dissimilar microclimatic conditions imposing particular constrains on incubating parents. Moreover, providing the best microclimate may conflict with parent?s needs to forage or conserve heat, particularly in single parent incubators. We examined the costs of incubation of the sordida  Orange-crowned Warbler breeding on Catalina Island, which shows great plasticity in nesting pattern (nest between 0 - 8 m). We compared ambient temperature, relative humidity, duration of incubation bouts and overall nest attendance between ground and above ground nests during incubation, using 2 channel hobo data loggers with probes inside nests. We contrasted egg desiccation rate between ground and above ground nests as the difference in egg mass measured twice during incubation. Ambient temperature and humidity fluctuated more at above ground nests, and females were exposed to higher ambient temperatures during the day but lower temperatures during the night than ground incubating females. Females incubating above ground took more but shorter bouts and spent on average less overall time attending their nest during the day than ground nesting females. Incubation periods at above ground nests were 1 d shorter (12 d) than ground nests. Ground nests had higher relative humidity during the incubation period and egg desiccation rates were lower relative to above ground nests. We will discuss possible female fitness consequences of microclimate differences among nest heights.