Has global warming become so powerful that Alaska is a better place to spend winter than Mexico?
Apparently, some Pacific brant -- a small, dark sea goose -- think so.
At least 30 percent of the Pacific brant population -- as many as 40,000 birds -- now winter in Alaska, said David Ward of the Alaska Science Center, lead author of a U.S. Geological Survey study of the species.
"This increase in wintering numbers of brant in Alaska coincides with a general warming of temperatures in the North Pacific and Bering Sea," said Ward.
Although records are sparse, Ward believes fewer than 3,000 brant wintered in the state before 1977. The new finding about more brant wintering in Alaska has raised concern that a severe cold snap could thin the already dwindling population of the birds, a subsistence food for some Western Alaska Natives.
Often called the "sea goose" because they never stray far from salt water, brant have a distinctive white necklace of feathers beneath a black head.
This time of year, brant from Alaska, Canada and Russia spend six to nine weeks on Izembek Lagoon on the Alaska Peninsula and adjacent areas near Cold Bay where they feed heavily on eelgrass. Those that migrate to Baja typically leave Izembek National Wildlife Refuge in huge flocks during late October or early November.
The brant population is estimated at 138,000 birds, said Dan Rosenberg, a biologist at the Alaska Department of Fish and Game. The population typically fluctuates between 110,000 and 165,000 birds, and it has been in a slow decline for nearly 40 years, Ward said.
Subsistence hunters statewide took 14,500 brant in 2007, with those in the Yukon-Kuskokwim Delta taking 5,000, Rosenberg said. Sport hunters in the Pacific Flyway stretching from Alaska to California killed another 2,840 birds.
The bag limit for sport hunters is two brant per day and four in possession, down a third from 2008 because of poor nesting conditions on the Yukon-Kuskokwim Delta. There are no bag limits for subsistence hunters.
A summer-long season runs April 2 through Aug. 31, with some in-season closures to protect nesting birds.
Despite a long-term population decline, Ward believes hunting has little or no effect.
"It's more linked to food resources on their feeding grounds," he said.
Warming conditions have affected the abundance and distribution of a variety of marine species, including the walleye pollock, Pacific cod, northern fur seal and thick-billed murre. Some biologists linked this summer's poor return of king salmon across much of Southcentral to warming seas.
Ward said the effects on species such as brant, which are restricted to estuarine ecosystems -- where rivers meet oceans -- had not been investigated.
"Our study suggests that the growth in the brant population wintering on the Alaska Peninsula is linked to this same climate change," Ward said.
Availability of eelgrass, a favored food of brant, may have prompted the shift.
Coastal environmental conditions have improved with the climate change. Higher temperatures mean less coastal sea ice, making nutrient-rich eelgrass accessible.
"Undisturbed access to sufficient amounts of eelgrass is likely crucial to the winter survival of this species," Ward said.
Ward expects that the number of Pacific brant wintering in Alaska will increase if the climate continues to warm.
But, he cautions, the picture is not entirely rosy for brant.
Even mild winters often include an extended bout of frigid weather with extensive shoreline ice. With more birds wintering in Alaska, these severe cold spells could put more of the brant population at risk, Ward said.
A cold snap that froze their food would prompt the birds to move -- first from Izembek to the south side of the Alaska Peninsula, then to offshore islands, the west end of Kodiak Island or even British Columbia -- in an effort to locate food.
"They would likely have reserves to fly south to B.C., but we don't know that," Ward said.
Wind may play a role in brant migration too.
Traditionally, the flow of southerly winds from low-pressure systems centered over the Aleutian Islands assisted southward-migrating brant on their way out of Alaska.
Now, there are fewer days each fall when brant have tailwinds to assist their 3,000-mile migration to Mexico. Ward and his colleagues believe this is a factor in more brant wintering in Alaska.
"Alaska now has the greatest concentration of Pacific brant outside of Mexico," said Ward. "They use the Aleutian lows to kick-start their migration south."
Reach reporter Mike Campbell at firstname.lastname@example.org or 257-4329.