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For some birds, a "taxi" helps recalibrate out-of-sync migrations


For some birds, a “taxi” helps recalibrate out-of-sync migrations

Pied flycatchers in the Netherlands were arriving late as climate change pushed spring earlier. Scientists drove them north to Sweden, and then they thrived.
September 27, 2023

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Pied flycatchers in the Netherlands have a problem. Evolution, with the help of a few scientists in a car, may have an answer.

Each spring, some of the small black-and-white songbirds, which could fit in the palm of your hand and weighs the equivalent of two quarters, make a transcontinental trek from wintering grounds in West Africa to summer nesting spots in the Netherlands.

But as climate change pushes spring earlier in northern Europe, the birds’ arrival is falling out of sync with the hatch of caterpillars which they feed to newly hatched nestlings. Scientists blame the mismatch for population declines of around 90% over two decades in some parts of the Netherlands.

Some of those same researchers wondered if these birds might have the capacity to adapt by changing their migratory habits—with a little assistance. For three springs, starting in 2017, scientists from the University of Groningen in the Netherlands and Sweden’s Lund University caught newly-arrived Dutch female pied flycatchers and drove them by car to a nesting spot 570 kilometers away in southern Sweden that was already home to other pied flycatchers.

That motor-assisted migration turned out to be a big boost for the newcomers. The move effectively rolled back the climate clock. They arrived in a place where spring—and the caterpillar emergence—typically starts two weeks later than in the Netherlands.


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And the new-found migration route stuck. The next year, the transplanted birds returned to Sweden, rather than to the Netherlands. But they held on to their old timing, meaning they were some of the first arrivals in the Swedish nesting grounds. In this case, the early birds got the caterpillars.

“The birds that were given a lift from the Netherlands to Skåne synchronized very well with the food peak. As they started to breed about 10 days earlier [than] the “Swedish” pied flycatchers they had a dramatically better breeding success than the Swedish ones as well as a better success than the pied flycatchers that remained in the Netherlands,” said Jan-Åke Nilsson, an ecologist at Lund University.

Within two years, the Dutch immigrants were producing more than twice as many surviving offspring as their Swedish counterparts, Nilsson and colleagues reported Sept. 14 in Nature Ecology & Evolution.

The scientists found evidence that this Dutch penchant for early migration is genetically hardwired. They swapped the eggs of two Dutch parents into the nests of Swedish birds to see whether the hatchlings followed the migratory habits of their genetic parents or the ones that raised them. In following years, the all-Dutch offspring arrived back in Sweden earliest, followed by birds hatched from one Dutch and one Swedish parent. The all-Swedish birds arrived the latest.

The results offer hope that at least some migratory bird species have enough genetic variability to adapt to climate-induced seasonal swings.

“By flying a little further north, these birds, at least in principle, could synchronize with their food resources, and there is hope that robust populations of small birds can be maintained, even though springs are arriving ever earlier,” said Nilsson.

These birds have also shown an ability to naturally shift their spring-time migratory destinations enough that it’s conceivable early-arriving Dutch birds might eventually reach Sweden on their own. Some Dutch fledglings have already been discovered breeding in Germany, half-way to Sweden. And those birds didn’t need to call a taxi.

Lamers, et. al. “Adaptation to climate change through dispersal and inherited timing in an avian migrant.” Nature Ecology & Evolution. Sept. 14, 2023.

Image: ©Anthropocene Magazine

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