These Birds Are Racing to Their Mating Grounds. It’s Exhausting.

Barnacle geese over England. Ideally, they arrive in the Arctic when the grasses, roots and mosses they eat are at their prime.
Credit...Hugh Clark/FLPA/Science Source

Geese have a problem. Some are arriving at their Arctic mating grounds so exhausted they’re not in the mood anymore.

Shifting environmental signals caused by global warming are making the birds race northward on their spring migration, flying faster and skipping the stops they normally use to rest and refuel, according to a study published Wednesday in the journal Current Biology.

Scientists said the finding was important because it gives new insight into the way climate change is altering the calculus of animal migration.

“This is the first one I know of where a long distance migrant is increasing its travel speed,” said Matthew P. Ayres, a professor of biology at Dartmouth College who was not involved in this study.

The birds in the study, barnacle geese, spend their summers in the Arctic, where warmer temperatures transform the snowy landscape into an all-you-can-eat buffet of grasses, roots and mosses.

Their migration is triggered by changes in daylight.As days grow longer in spring, the geese take sunlight as a cue to head north. The goal is to arrive early enough in the spring to take advantage of the tender spring greens that are especially beneficial for chicks.

But as human-caused climate change shifts weather patterns, spring arrives earlier in the Arctic some years.The birds, snug in their southern wintering grounds, don’t know that. And, critically, they don’t know that they should get an early start.

Once the birds are en route, environmental cues like lots of greenery make them realize that spring has arrived early in the north. The barnacle geese change their behavior, increasing airspeed and skipping the avian rest stops that they ordinarily use to fuel their travel and to fatten themselves up for the weeks of egg-laying ahead.

The geese take the time to rebuild their strength when they arrive, but that means nesting is delayed.

As a result, their chicks are born when the food supply is past its prime. They “hatch while the vegetation is already not optimal and they grow less and they survive less,” said Bart Nolet, a professor at the Netherlands Institute of Ecology and an author of the study.

Barnacle geese are good research subjects because they’re both abundant and large.

It’s only recently that GPS trackers and accelerometers — which let the researchers track not only the location of birds but also behaviors like foraging, resting and flying — have been made small enough to fit on smaller birds. But for bigger birds, there’s good historical GPS data.

In the case of the barnacle geese the news isn’t all bad: Their population numbers are stable-to-increasing. The researchers think that, in the years when spring arrives early, the reduced number of chicks is balanced out by an increased number of chicks who survive the winter because of less competition for food.

But what worries the researchers is that the changes in the Arctic are still within the range of natural variation — the birds have had to deal with this before to some degree. But the Arctic is warming faster than any other region on Earth, and eventually spring may come much, much earlier. Farther ahead of schedule than birds have ever dealt with.

That doesn’t only apply to geese.

“All of these birds are confronted with the advancement in the spring and the fact that it’s not coupled with changes in the wintering areas,” Dr. Nolet said.

Dr. Ayres agreed. “Presumably there will be a point where they’re no longer leaving on time if they stick to their old schedule,” he said. “And then we’ll be learning how rapidly, if at all, these timing mechanisms can evolve.”

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