As snow melts earlier on the coastal tundra of Alaska's North Slope, the migrating shorebirds that fly there each summer seem to be responding by hurrying their nesting activities, according to a study published online in the journal Polar Biology.
"This is all part of a package deal -- earlier springs leading to earlier retreat of snow and ice leading to earlier nesting of the birds," said Steve Zack of the Wildlife Conservation Society of North America, one of the scientists who authored the study.
The scientists spent nine summers on the flat tundra, studying four areas with varying features -- two within the industrialized Prudhoe Bay and Kuparuk oil fields and two in the remote, wilder territory near Teshekpuk Lake, the North Slope's biggest freshwater body.
They monitored more than 2,400 nests made by five bird species -- semipalmated sandpipers, pectoral sandpipers, red-necked phalaropes, red phalaropes and Lapland longspurs -- recording nest sites using GPS instrumentation and watching for egg production and hatching.
Zack said he was "really impressed and even a bit startled" by the results, which showed that the birds are nesting 0.4 to 0.8 days earlier each year.
"Birds are advancing the time of their nesting, on average, a full day every two years," he said.
That schedule shift could mean trouble, creating what scientists call a "phenological mismatch" -- a disruption in timing that has evolved for species' optimum development.
Other recent studies have focused on such mismatches and the possibility that a warming climate, especially in the far north, is driving them.
A study by scientists from Denmark's Aarhus University, published November in the journal Oecologia, found that spring is arriving two weeks earlier in Svalbard, and the East Atlantic light-bellied brent geese that spent their summers there might be migrating too late to find optimum nesting conditions.
Faster retreat of Arctic sea ice may be creating another timing problem for snow geese in Hudson Bay, where polar bears that once focused on hunting seals from the ice are now onshore at the same time those birds are nesting and incubating their eggs, according to a study by scientists at the American Museum of Natural History that was published in 2011 in the journal Oikos.
There are concerns that climate changes are disrupting timing of plant blooms and arrival of the animals that pollinate them, with research summarized in study published in April in Natural Areas Journal.
The North Slope birds that he and his research partners studied, Zack said, showed some of the most dramatic seasonal shifts documented to date. That is cause for concern because the timing shifts might be causing problems for birds that have to fly thousands of miles in relatively short periods of time, he said.
But whether the North Slope birds have changed their migratory schedule is yet to be determined.
"We know they're breeding earlier, but we don't have the data to indicate whether arrival is happening earlier," he said.
The different bird species studied had slightly different nesting schedules. Pectoral sandpipers, which have low nest-site fidelity, appeared to be strongly influenced by timing of green-up, according to the study. Phalaropes, which prefer wet tundra for their nests, seemed to be influenced by the timing of snowmelt, according to the study.
The study did not track the birds' food sources, but it notes that in general, more food is available to birds when snow melts.
Predators had no effect on the nesting schedule, according to the study, giving no support to the theory that birds are nesting earlier to avoid predators.
The researchers surveyed the territory around the nesting bird three times each year to locate and count predators. They found that predator abundance fluctuated widely and had no correlation to birds' nesting or egg-laying schedules, but sites three times a year to locate and count predators.
Reach Yereth Rosen at firstname.lastname@example.org.
By YERETH ROSEN