Effects of Experience and Body Weight on Incubation Behavior of Canada Geese

During 1979 and 1980, we studied the incubation behavior and body-weight dynamics of captive Canada Geese (Branta canadensis moffitti) with known breeding histories. Females were attentive to their nests for 97.5% of the incubation period and lost 27% of their initial body weight. Heavier females were more attentive to their nests and lost more weight during incubation than did lighter females. Variation in body weight among females was greatest at the onset of incubation and least at hatch, which suggests that females invested maximum reserves in incubation. Recess frequency and duration increased throughout incubation, resulting in more foraging time for the female. Once a lower critical weight of about 3,200 g was reached, the amount of recess time taken increased dramatically, probably because lipid reserves were depleted. Females nesting for the first time began incubation at a lighter body weight and were less attentive than experienced females. All inexperienced females were either 4 or 5 yr old, but their egg production (4 eggs) was that of 2- or 3-yr-old wild females. This indicated that experience rather than age was the important variable affecting acquisition of reserves. Inattentiveness to a nest by a female prolongs the duration of incubation and exposes the nest to a greater risk of predation. The inability of inexperienced females to gain enough reserves to provide for both maximum clutch size and attentiveness during incubation may be a major explanation for the lower hatching success of geese nesting for the first time.