The Influence of Female Age, Body Mass, and Ambient Conditions on Redhead Incubation Constancy

Abstract

Incubation constancy, i.e., the proportion of time on the nest, of female Redheads (Aythya americana) was examined during the summers of 1995 and 1996 in relation to female age, body mass, and ambient conditions. Redhead females exhibited one of the lowest incubation constancy (82%) among duck species (Anatidae), coupled with a comparatively high number of incubation recesses per day. Low constancy was not due to excessive disturbance at the nest or reduced maternal investment in the clutch, but was probably related to energetic constraints of the female imposed by laying parasitic eggs prior to nesting. As in most other duck species, incubation constancy decreased over the incubation period. Age, mass, and maximum daily temperature, and the interactions of initiation day × age and mass × date significantly influenced daily incubation constancy. Constancy was higher for older females and for females of lower body mass and was lower on days with higher maximum daily temperatures.