Why Snow Geese Are Booming in Arctic Alaska

A snow goose. Photograph by Ryan Askren, U.S. Geological Survey.

Through its Changing Arctic Ecosystems initiative, the U.S. Geological Survey gives resource managers science on how Arctic Alaska is responding to a warming climate. A key study area is the Arctic Coastal Plain of northern Alaska, where recent decades have brought less sea ice, thawing permafrost and earlier springs. The bird life is changing too: all four goose species that nest there are increasing, and the snow goose (Chen caerulescens) fastest of all.

A comeback

Snow geese have multiplied across North America over the past six decades, damaging vegetation where they nest and harming other birds, mainly in Arctic Canada. Once common in northern Alaska, they were largely wiped out by people by the early 20th century, and only a remnant of fewer than 1,000 birds nested on the coastal plain through the latter half of the 20th century. U.S. Fish and Wildlife Service surveys show that Alaska's population, about 35,000 birds, is still small beside the millions nesting in Canada, but growing rapidly.

What USGS found on the Colville River Delta

Since 2011 the USGS has studied how snow geese on the Colville River Delta are responding to warming, and what their rise means for other birds.

• Earlier arrival. Compared with 15 other species that commonly nest on the coastal plain, snow geese have moved their arrival forward more than most over the past 30 years.
• Earlier hatching. They nest earlier and hatch their young 4–7 days before black brant (Branta bernicla nigricans) and white-fronted geese (Anser albifrons). That gives goslings first access to the best food, so they grow bigger, which helps them survive autumn and winter, join the breeding population and breed well as adults.
• More young. In most years snow geese had higher nest survival and raised as many as 25 percent more goslings than neighbouring brant or white-fronted geese, and more female snow geese than female brant returned to the Arctic.
• Little hunting pressure. Band recoveries suggest hunters in North America take less than 3 percent of the adult snow geese nesting in Alaska.
• Immigration from Canada's huge populations may be adding birds as well.

Figure 1: Average hatch dates, relative to the earliest nest each year, 2011–2014, Colville River Delta. Snow geese hatch 4–7 days before brant and white-fronted geese, reaching brood-rearing areas first. USGS.

USGS captures and bands snow geese in late summer, when they cannot fly. Recoveries and recaptures of banded birds give estimates of adult and juvenile survival and of hunting harvest, and late-summer captures measure how fast juveniles grow, a sign of habitat quality. Photograph by Jerry Hupp, U.S. Geological Survey.

What lies ahead

Earlier USGS work found that warming has made conditions on the coastal plain good for geese to breed and moult. On the Colville delta, habitat for broods is good and juvenile snow geese grow faster than elsewhere in the Arctic, so habitat is unlikely to hold the population back soon. With strong breeding, high adult survival, plenty of good habitat and perhaps immigration, snow geese will probably keep increasing; at the current rate, the Fish and Wildlife Service calculates, the coastal plain population could double every 3–4 years.

A snow goose at its nest. Photograph by Ryan Askren, U.S. Geological Survey.

What's next

Warming works both ways on goose habitat: sinking coastlines create rich feeding areas, while faster coastal erosion destroys habitat. The USGS is building forecasts of habitat that weigh both, which, with continued studies of snow goose survival and breeding, will allow population projections. Habitat studies will measure what more geese do to Arctic plants and find brood-rearing areas not yet used, and the USGS is assessing whether more snow geese will harm the black brant that share their nesting and brood areas, information agencies need to weigh the effects and their options.

A black brant defends its nesting territory against snow geese. Photograph by Ryan Askren, U.S. Geological Survey.

Sources

• Jerry Hupp, David Ward, Mary Whalen and John Pearce, Changing arctic ecosystems—What is causing the rapid increase of snow geese in northern Alaska?, U.S. Geological Survey Fact Sheet 2015–3062. https://pubs.usgs.gov/publication/fs20153062