Snow geese and white-fronted geese are gorging on what amounts to an early bird special on Alaska's North Slope, thanks to their ability to adapt to warming Arctic conditions, according to new research from the U.S. Geological Survey and other organizations.
A USGS-led study finds that white-fronted geese, snow geese and other species of birds that nest in the Colville River Delta have been arriving earlier and earlier at a steady pace over the last half century. The 16 studied species are, on average, arriving six days earlier, a rate of change of about 0.12 days per year.
Of those 16 species, greater white-fronted geese and lesser snow geese altered their arrival pattern the most, according to the study, advancing by an annual average of 0.19 days and 0.18 days respectively.
The arrival-date study uses five decades of detailed observations by Jim Helmericks and his family, residents of a unique Alaska homestead within the Colville River Delta. Helmericks is a co-author of the study, published online in the Journal of Avian Biology. "He's quite an observer and naturalist," said USGS wildlife biologist David Ward, the lead author.
The Colville is a major Arctic river. Its delta -- a fan of braided channels where vast quantities of freshwater originating from the Brooks Range pour into the Arctic Ocean -- is the largest on the North Slope, and is famous as a haven for migrating birds and other Arctic wildlife.
The area has become particularly fertile ground for snow geese, related USGS research found. The Colville-nesting population, which fell victim to overhunting in the early 20th century and was down to a remnant of about 1,000 birds by the second half of the century, has now rebounded to 35,000, according to the USGS and the U.S. Fish and Wildlife Service.
Snow geese are not only arriving sooner; they are also nesting more quickly, producing hatchlings four to seven days earlier than other geese that use the area, like black brant.
"They arrive earlier. They nest earlier. They tend to have higher nest success than every other species that we've looked at," Ward said. "Those young have first dibs, if you will, on the high-quality food resources." That means the young are able to grow bigger faster, and "the larger you are, the better survival you have," he said.
Geese are thriving on the North Slope for other reasons, too.
Black brant have increased dramatically in number on the North Slope, thanks to some changes brought about by the warming climate. Sags in thawing permafrost are changing hydrology and favoring the salt-tolerant plants that are most beneficial to brant, according to research by the scientists from the USGS and University of Alaska Fairbanks.
In the short term, "there's plenty of food" for all the geese nesting in the Colville River Delta, even as their populations increase, Ward said. But that might not be in the case in the long term, he said. If populations get big enough, "there's going to be competition between birds," he said.
Among the 16 species examined in the nesting-arrival study, snow buntings -- though they have not advanced their timing as dramatically as the geese -- reach the Colville nesting sites the earliest in the year, in mid-April. The latest arrivals are red-throated loons and yellow-billed loons, which arrive at the start of June, according to the records.
The loons have also been the least successful at advancing their arrival, according to the study. Yellow-billed loons' first arrival changed by only 0.09 days per year over the 50-year period, and red throated loons' by only 0.08 days per year.
The loons and other birds, like ducks and gulls, that are advancing their arrival more slowly "may be at greater risk of a phenology mismatch over time," the study says, referring to the scientific term for seasonal timing of biological events.
In general, shorebirds appear to be having trouble adapting, Ward said. They are also the birds that migrate the longest distances, from as far away as South America and New Zealand, compared to the geese, which migrate from as close as the western states of the Lower 48, he said.
Overall, local temperature appears to be the main driver behind all species' earlier arrival at the nesting sites, according to the study. Using available temperature records, the scientists calculated an average 1.03-day earlier arrival for every 1 degree Celsius (1.8 degree Fahrenheit) change in annual temperature.
But even for snow geese, there appears to be a limit to the ability to adapt to Arctic warming.
On Canada's Bylot Island, located farther north than the Colville River Delta, snow geese have also been advancing their nesting -- but not fast enough to give their goslings access to the fresh new plants with peak nutritional value, according to a separate study in the journal Global Change Biology. That recently published study, led by scientists at Laval University and focusing on the years from 1991 to 2010, found mismatches of up to 20 days between the emergence of the best-quality plant food and the hatching of goslings.