Climate Change Puts Bird Migration on Ice
A family of brants on the Yukon-Kuskokwim Delta in Alaska. Photo by Jeff Wasley, U.S. Geological Survey via USGS.
It seems every time we turn around, climate change is throwing away the rule book. This time, the problem is with a species of bird that is staying put in the winter months instead of migrating south.A new report from the U.S. Geological Survey published in Arctic reveals the Pacific brant, a small sea goose, is now wintering in sub-Arctic areas.
In the past, 90 percent of the bird's population wintered in Mexico, with the rest scattered up the Pacific coast, but now nearly one-third spend winters in Alaska. To put this in perspective, less than 3,000 birds stayed in Alaska over the winter before 1977; today, the number wintering at home is 40,000.
One of the reasons for this significant shift in migration patterns is winter conditions have become more hospitable as a result of global warming, says David Ward, lead author of the study and USGS researcher:
This increase in wintering numbers of brant in Alaska coincides with a general warming of temperatures in the North Pacific and Bering Sea. This suggests that environmental conditions have changed for one of the northernmost-wintering populations of geese.
The link between climate and change in migration is a two-part story, with changes in winds playing a key role. The 3,000-mile migration brants took from Alaska to Mexico was once aided by a tail-wind. But the USGS research has established a link between brants staying in Alaska and the fewer number of autumn days when the winds flow southerly, indicating the birds rely on favorable winds to help them get to their wintering grounds.
It also appears the shift in migration has to do with availability of food. Brants' primary food, eelgrass, is now abundant in Alaska in the winter, and when combined with warmer air and water temperatures, living conditions are much more favorable than they were in the past. Still, favorable does not mean optimal, say researchers.
Scientists are predicting that climate change also brings more variability in conditions, which means severe cold snaps could be expected in areas that are generally seeing considerably warmer temperatures. This type of weather episode could put the entire brant population at risk, says Ward:
Alaska now has the greatest concentration of Pacific brant outside of Mexico. Because of this, threats to the Alaska wintering population can affect the entire Pacific Flyway population.