Some pink-footed geese have begun migrating to the Arctic island of Novaya Zemlya in the summer to breed, nearly 1000 kilometres away from their usual breeding site on the island of Svalbard.
Conditions on Novaya Zemlya, a Russian island in the Arctic, used to be too cold for breeding geese. But with spring conditions coming earlier in the year because of global warming, the island has become suitable, says Jesper Madsen at Aarhus University in Denmark. Over 15 years or so, this population has established a new migration route to Novaya Zemlya and new stop-over points along the way.
“It’s a huge surprise,” says Madsen. “It’s really amazing to see this.”
Some other birds have been changing their ranges in response to global warming, but this is the most dramatic shift of this kind ever observed in a migratory bird, he says.
There are two populations of pink-footed geese (Anser brachyrhynchus). One overwinters in the UK and Ireland and migrates to Iceland and Greenland to breed in summer.
The other overwinters in the Netherlands and Denmark, migrating to Svalbard to breed. In spring, this population flies along most of the length of Norway, resting in places, before the long flight over the sea to Svalbard. The birds return along this route in autumn.
But, in the 1990s, people began spotting individuals and small flocks of pink-footed geese in southern Sweden during spring and autumn. By the 2000s, larger flocks were frequently being spotted.
To find out where they were going, in 2018 and 2019, Madsen and his colleagues put GPS tags on 21 geese. Half of them flew to a part of Novaya Zemlya that was used for testing nuclear bombs up until 1990. Not even Russian biologists are allowed to go there, says Madsen, so their presence wouldn’t have been discovered without the GPS trackers.
These birds are migrating over Sweden and Finland rather than flying along Norway, and the GPS data also shows that the birds are nesting there. Many are returning with offspring.
The researchers estimate that the Novaya Zemlya population has grown to around 4000 birds already. Because of routine non-GPS tagging of some birds along the Denmark to Svalbard route, they have been able to tell that some of these geese were previously travelling to Svalbard and have switched routes, with young geese mostly likely to change.
The team’s hypothesis is that these geese learned the new migration by copying taiga bean geese (Anser fabalis). Some taiga bean geese fly to Novaya Zemlya in late spring to moult and replace their flight feathers, rather than to breed.
“That’s the best explanation we have,” says Madsen. If correct, it would be a rare example of cultural knowledge transmission occurring between species.
Madsen thinks the shift is happening not just because of the warming of Novaya Zemlya, but also because of increasing difficulties with the traditional migration route. Pink-footed geese are now having to compete with barnacle geese (Branta leucopsis) for food at stop-overs, and changes in farming practices are also reducing food availability.
“This is a really neat study that combines traditional, old-school bird observations and counting, with tagging, GPS and climate data, to uncover a remarkable new story,” says Richard Gregory at the RSPB Centre for Conservation Science in the UK, who wasn’t involved in the study.
“On the one hand, it provides hope that migratory bird species might be able to respond to climate change over relatively short periods, but raises alarm bells over the pace of change,” he says.