Survival and brood rearing ecology of emperor geese

Abstract

Emperor Geese (Chen canagica) breed on the Yukon-Kuskokwim Delta in an area inhabited by three other goose species. Whereas populations of other geese increased since the mid 1980s, Emperor Goose numbers remained low. Because survival and habitat selection by broods of Emeperor Geese had not been studied previously and numbers of predatory Glaucous Gulls (Larus hyperboreus) had recently increased, I studied brood rearing ecology of Emperor Geese during 1993-1996 to assess whether this seasonal period could be limiting population growth. Survival of goslings to 30 days varied among years from 0.32 to 0.70 and was primarily influenced by mortality during the first five days after hatch. Other goose species with similar rates of gosling survival are increasing rapidly. Survival of Emperor Goose goslings was lowest in 1994, when unusually heavy rainfall occurred during early brood rearing. Using a long-term data set from Izembek National Wildlife Refuge, sizes of families in fall (n=23 years) were related to rainfall during early brood rearing. Gosling survival was lower and gull disturbance of broods greater in 1993-1994 than in 1995-1996. Although goslings wer commonly consumed by Glaucous Gulls, gull diets during 1993 were similar to those observed in the 1970s. Across a broad scale, broods of Emperor Geese (n=56) strongly selected habitats dominated by Carex subspathaceae, Carex ramenskii, and unvegetated areas interspersed among these forage species, as determined from telemetry. These selected habitats comprised one-third of all available habitat. Habitat selection by the composite goose community (dominated by Cackling Canada Geese [Branta canadensis minima]) was assessed by feces collections and differed substantially from that of Emperor Geese. Broods of Emperor Geese spent more time feeding during 1993-1996 than during an earlier study in 1985-1986. During 1994-1996, feeding rates of gosling and adult females was related more to total goose density than to Emperor Goose density. Although Cackling Canada Geese exhibited strongest selection of other habitats, their greater overall abundance resulted in numerical equivalence to Emperor Geese in habitats preferred by Emperor Geese. Interspecific competition for food has impacted behavior in Emperor Geese, which may impact growth and survival of juvenile geese.