Abstracts

Presented by Mitch D. Weegman - Email: weegmanm@missouri.edu

Migratory birds often face substantial risk as they travel between breeding and wintering areas annually. Spring migration is particularly risky because individuals must store energy for migration and reproduction. Hence, individuals attempt to time movements to optimize energy acquisition relative to expenditure, and poor decisions could reduce the probability of a successful reproductive attempt. Weather conditions also impact probabilities of breeding; even the best decisions may be negatively influenced later by poor weather conditions. We used GPS/acceleration tracking devices to test whether variation in the proportion of time feeding during spring explained variation in reproductive attempt or deferral, and quantified the extent to which local weather conditions explained variation in the proportion of time feeding in two populations of greater white-fronted geese (Anser albifrons) that show opposite population trajectories and have substantially different migration strategies. Our data suggest seven individuals (64%) from the midcontinent population and 13 individuals (48%) from the Greenland population initiated a breeding attempt. Variation in the proportion of time feeding during spring migration explained substantial variation in reproductive attempt or deferral only during the final stage of migration in midcontinent birds. Greater variability in the proportion of time feeding throughout spring migration dramatically increased the probability of a breeding attempt in Greenland birds, whereas the relationship was positive but not as pronounced for North American birds. The relationship between the proportion of time feeding and temperature varied by time period, but was consistently positive for both populations. However, the relationship between the proportion of time feeding and precipitation was negative for Greenland birds but positive for midcontinent birds, primarily as birds approached breeding areas. These results suggest that differences in behavior and subsequent reproductive attempts between populations are in part explained by migration strategies but also constraining local weather conditions.