Patterns of Brood Dispersal and Habitat Use in Emperor Goose (Anser canagicus) Goslings: Behavioral and Ecological Insights

Background Animals make decisions about habitat use that have lifelong implications for survival and fitness. For waterfowl, decisions made between hatching and fledging are especially important, as precocial young must not only grow and complete their molt but also prepare for their first fall migration. Methods To better understand how emperor goose broods navigate heterogenous habitats during the brood rearing period, we deployed GPS transmitters on females with broods to track gosling movements on the Yukon-Kuskokwim Delta, Alaska. From this GPS data, we determined distance traveled by broods from the nesting site, brood home range size, types of habitats used, and resource selection. These results were compared to previous work on emperor goslings from the late 1990s and early 2000s. Results We found that emperor goose broods stayed within 5km of their nesting site and maintained an average home range of ~ 10km ² . Both grazing lawn and mudflat habitats were present within their home range but broods preferentially selected grazing lawns. Broods were observed to forage for algae on mudflat and Carex sedges on grazing lawns. Conclusions Our results reveal that grazing lawn remains the most important habitat for brood-rearing emperor geese on the Yukon-Kuskokwim Delta, consistent with past studies; however, broods also appear to regularly forage on green algae present on mudflats when these areas are available during low tide. This is the first-known study that has documented emperor goslings extensively using non-vegetated mudflat habitats, which provide forage while allowing adults to better observe incoming predators and competing species. We also found that females and their broods travel short distances to reach brood-rearing sites and that home range size varied based on individual, not habitat used. Overall, their dependence on grazing lawns, combined with long-term declines in these habitats across the Yukon-Kuskokwim Delta, may have lasting implications on fitness of emperor goose broods.