W.D. Eldridge | Geology Reports

USGS2008

Body mass of prefledging Emperor Geese Chen canagica: Large-scale effects of interspecific densities and food availability

We studied body mass of prefledging Emperor Geese Chen canagica at three locations across the Yukon–Kuskokwim Delta, Alaska, during 1990–2004 to investigate whether large‐scale variation in body mass was related to interspecific competition for food. From 1990 to 2004, densities of Cackling Geese Branta hutchinsii minima more than doubled and were c . 2–5× greater than densities of Emperor Geese, which were relatively constant over time. Body mass of prefledging Emperor Geese was strongly related (negatively) to interspecific densities of geese (combined density of Cackling and Emperor Geese) and positively related to measures of food availability (grazing lawn extent and net above‐ground primary productivity (NAPP)). Grazing by geese resulted in consumption of ≥ 90% of the NAPP that occurred in grazing lawns during the brood‐rearing period, suggesting that density‐dependent interspecific competition was from exploitation of common food resources. Efforts to increase the population size of Emperor Geese would benefit from considering competitive interactions among goose species and with forage plants.

Ibis↗

USGS2007

Moult migration of emperor geese Chen canagica between Alaska and Russia

We studied reproductive success and post-breeding movements of 32 adult female emperor geese Chen canagica that were marked with satellite radio transmitters on their nesting area on the Yukon-Kuskokwim Delta (YKD), Alaska 2000–2004. All 16 females that failed to successfully reproduce departed the YKD and moulted remiges either on the north coast of the Chukotka Peninsula, Russia (n=15), or on St. Lawrence Island, Alaska (n=1). Of 16 females that successfully nested, one migrated to Russia following hatch whereas the remainder stayed on the YKD. While moulting on the Chukotka Peninsula, emperor geese with satellite transmitters primarily used coastal lagoons west of Kolyuchin Bay. We observed 21,150 adult-plumaged emperor geese during aerial surveys in Chukotka in 2002. Most (95%) were in the same region used by geese that had been marked with satellite transmitters in Alaska. The number of emperor geese observed in Russia was comparable to our estimate of ≥20,000 adults that either do not nest or nest unsuccessfully each year on the YKD, suggesting that most nonproductive adults, or ≥28% of the adult population departs the YKD to moult elsewhere. The number of moult migrants may be substantially higher in years of poor reproductive success or if adult-plumaged birds that are not of breeding age also leave the YKD. Moult migration of emperor geese between Alaska and Russia is likely substantially greater than previously believed. Russian moulting habitats are important to the North American population of emperor geese and events that affect survival of geese in Russia could impact population trends on the YKD. Protection of coastal lagoons on the north coast of Chukotka is warranted.

Journal of Avian Biology↗