با رسیدن بهار قو ها به مهاجرت خود سرعت می بخشند

Every spring, a bird called the barnacle goose migrates from the coast of the North Sea to the Russian Arctic, where it breeds. That’s a 3000-kilometer trip. Along the way, the geese usually take pit stops to rest and refuel. But the Arctic spring has been arriving earlier and earlier.

So researchers analyzed six years of barnacle goose migratory tracking data. To try to figure out if these geese—and other species like it—can adapt their migration, to stay in sync with the changing seasons.

“Then we used satellite images to see when snow was melting in the Arctic, and then we could relate the timing of the birds to the snow melt.” Bart Nolet, an ecologist at the University of Amsterdam.

Nolet and his colleagues found that the geese did not leave their wintering grounds sooner to match the earlier Arctic spring. But they did speed up their trip—by skipping many of their usual stopovers. The birds arrived in the Arctic up to 13 days earlier than they used to. But at a cost.

“So in a normal year, they start laying their eggs right after arrival. But now they spent more than a week foraging before they laid their eggs…. So in effect, they weren’t that much earlier than would have been the case. As a result, the chicks that hatch from the eggs in that early year, they survive much less than normal. Probably because they missed the food peak, which is a combination of very high quality in the grass, and enough grass around. And that food peak is around three weeks after snow melt, but now they were a few weeks later.”

With devastating effects.

“We looked at the daily survival of the goslings. If you calculate it over the whole month, then it’s quite dramatic, they decrease from 20 percent to only 2 percent surviving. It basically means that not many goslings are surviving in such a year.” The study is in the journal Current Biology.

So why don’t the geese just leave their wintering grounds earlier?

“When it’s an early spring in the Arctic, it’s not necessarily an early spring in the wintering area. So the birds cannot use any cue that’s related to what’s early or late spring to leave.”

But Nolet does think there’s some hope they might be able to adapt. “We know that the goslings learn their migration from their parents, so there’s a lot of learned behavior in it. So it may well be that in the course of time, some birds discover that they have to depart earlier from their wintering areas to be able to time their migration perfectly, and match it with the Arctic.”