Incubation temperatures of the northern shoveler

Abstract

Egg air cell and nest air temperatures, measured in nests of wild northern shovelers near Delta, Manitoba, Canada, averaged 36.1 and 32.0 °C, respectively. Mean brood patch temperature of one captive incubating hen was 39.5 °C. Body temperature of 16 wild incubating hens averaged 41.1 °C. An egg cooling rate of 0.22 °C/1 °C h−1 was calculated from temperature records of 170 incubation recesses. Factors affecting egg cooling during recesses were investigated using multiple regression analysis. Statements in the literature that incubation by Anatidae begins upon termination of laying are not supported by available data. Incubation by waterfowl, as in passerines, apparently begins gradually during the laying period. Air and ground temperatures, by influencing egg cooling rates during incubation, may have been important ultimate factors determining the breeding range and timing of the breeding season for the northern shoveler.