Alaska Science Center
Researchers at the USGS, Alaska Science Center, are conducting life history and demographic studies of two migratory waterfowl species—Pacific black brant and emperor geese—to help understand the epidemiology of avian influenza and other pathogens. These Alaska nesting geese were selected for detailed studies because they migrate between the Asian and North American continents and are considered high priority species for monitoring for the presence of the H5N1 subtype of highly pathogenic avian influenza. In addition to routine sampling and testing these species for the presence of avian influenza viruses, we collect information on adult survival, productivity, gosling growth rates, body mass dynamics, and other vital rates useful in understanding the impact of pathogens on population demographics of host species.
Recent declines in black brant (Branta bernicla nigricans) are likely the result of low recruitment. In geese, recruitment is strongly affected by habitat conditions experienced by broods because gosling growth rates are indicative of forage conditions during brood rearing and strongly influence future survival and productivity. In 2006-2008, we studied gosling growth at 3 of the 4 major colonies on the Yukon-Kuskokwim Delta (YKD), Alaska. Estimates of age-adjusted gosling mass at the 2 southern colonies (~ 30% of the world population of breeding black brant) was low (gosling mass at 30.5 days ranged from 346.7 ± 42.5g to 627.1 ± 15.9g) in comparison to a third colony (gosling mass at 30.5 days ranged from 640.0 ± 8.3g to 821.6 ± 13.6g) and to most previous estimates of age-adjusted mass of brant goslings. Thus, our results are consistent with the hypothesis that poor gosling growth is negatively influencing the brant population. There are 2 non-mutually exclusive explanations for the apparent growth rates that we observed. First, the population decline may have been caused by density-independent factors and habitat capacity has declined along with the population as a consequence of the unique foraging feedback between brant and their grazing habitats. Alternatively, a reduction in habitat capacity, as a result of changes to the grazing system, may have negatively influenced gosling growth and this is contributing to the overall long-term population decline. We found support for both explanations. For colonies over habitat capacity we recommend management to enhance foraging habitat, whereas for colonies below habitat capacity we recommend management to increase nesting productivity.
Contact: Tom Fondell
Geese use varying movement strategies in conjunction with wing molt - successful breeders with broods are constrained to molt closer to nesting sites, whereas failed breeders and nonbreeders can move to molting sites, often considerable distances away. One hypothesis for movement away from breeding grounds is to avoid competition with broods and to gain access to higher quality forage. To examine this hypothesis we captured black brant (Branta bernicla nigricans; hereafter brant) during the molt on both brood rearing and non-breeding areas. The primary breeding area for brant is the Yukon-Kuskokwim Delta (YKD) but the largest molting concentration is found >1000 km north in the Teshekpuk Lake Special Area (TLSA) on the arctic coastal plain. We captured brood rearing brant on the YKD and flocks of failed or non-breeding brant on both the YKD and the TLSA. We used 9th primary length as a measure of molt stage. At the initiation of wing molt, body mass of brant at the TLSA > YKD molting adults without young > YKD brood rearing area. Brant at all three areas lost mass during molt. Rates of mass loss among areas were directly related to initial mass; rate of mass loss at TLSA > YKD molt area > YKD brood area. Loss of mass during molt may be an adaptation to allow birds to regain flight as early as possible. Thus, birds starting molt at a higher mass, lose more weight. Our results suggest that one advantage of undertaking the > 1000 km molt migration to the TLSA may be to increase body mass prior to molt as a hedge against poor conditions during molt. Further, because of mass loss during molt, access to high quality forage conditions after completing molt may be important to replenish lost reserves prior to migration.
Contact: Tom Fondell
Nearly the entire world’s population of Emperor Geese (Chen canagica) breed in western Alaska, where they are a traditional subsistence food resource for local people. Unlike other North American geese, virtually all emperor geese spend a portion of their life cycle (summers in nonbreeding years) in east Asia, principally in the Chukotka region of Russia. This geographic distinction may make Emperor Geese more likely to encounter virulent forms of avian influenza. This hypothesis is supported by the fact that on the principal breeding area, the Yukon-Kuskokwim Delta, where four species of geese nest sympatrically, Emperor Geese exhibited much higher prevalence of antibodies to avian influenza virus than the other three species (Cackling Geese, Greater White-fronted Geese, and Black Brant). The pathology of viruses can exert significant demographic impacts on populations of birds (e.g., West Nile virus on Corvids, in some regions). The demographic impact of avian influenza viruses on wild bird populations is unknown, but our work in western Alaska provides an opportunity for such an evaluation. In addition to significant exposure to avian influenza viruses, our study population is saturated with many uniquely marked individuals so that we can relate characteristics of individuals, including their viral status, to their propensity to survive and raise young.
Contact: Joel Schmutz