A new study conducted by an international research team with Danish participation reveals that many Arctic-breeding waterbirds still possess a degree of flexibility when it comes to accelerating their migration. However, this strategy may only be effective for a limited time.

Published in Nature Climate Change, the study tracked spring migration of five large waterbird species using GPS: brent goose, barnacle goose, white-fronted goose, pink-footed goose, and Bewick’s swan.

By combining tracking data with body mass measurements collected from birds in their wintering areas, researchers discovered that these birds can reduce the time spent refueling for their journey – allowing them to speed up spring migration.

The results are both encouraging and concerning. While the birds can migrate faster by adjusting their stopovers and foraging behaviour, time is running out. Predictions suggest that their flexibility may only compensate for the rapidly advancing Arctic spring for a few more decades.

Dependent on a large “packed lunch

Refueling of fat reserves begins even before migration starts. This is especially important for species like barnacle and brent geese, which undertake long non-stop flights (over 2,000 km) and are therefore highly dependent on energy stores built up before departure.

Species vary in their flexibility in responding to changing spring conditions.

In years when the Arctic thaws early, species like the white-fronted goose and Bewick’s swan shorten their stopovers along the migration route and arrive earlier.

Lisa Vergin from Aarhus University has tagged Bewick’s swans.
“Bewick’s swans make relatively many stops on their way from the Wadden Sea area to their breeding grounds in northern Russia. They can track spring conditions and adjust their stopover durations accordingly,” she explains.

However, species like the pink-footed goose and brent goose show less ability to adapt en route. This is linked to their fewer stopover sites and inability to assess conditions at the breeding grounds.

Professor Jesper Madsen, also from Aarhus University, studies pink-footed geese breeding in Svalbard, which face greater challenges due to climate change.
“The pink-footed geese cannot predict weather conditions in Svalbard when migrating from Denmark to Norway and then flying non-stop across the Arctic Ocean to reach Svalbard. They must be cautious to avoid arriving to a tundra still covered in snow, with no access to food or nesting sites,” says Jesper Madsen.

His research in Svalbard shows that breeding success is entirely dependent on when the snow melts. In an early year like 2025, the snow had already melted when the geese arrived in mid-May.
“They can start laying eggs within a week, have good body reserves, and achieve high breeding success. But in a late spring like 2021, the geese had to wait a long time for the snow to melt, and the breeding season collapsed—likely because they ran out of body reserves,” says Jesper Madsen.

Breeding on a knife’s edge
For migratory birds, arriving in the Arctic on time is crucial for breeding success and survival. When spring arrives and the snow begins to melt, there is an explosion of insects, plants and other food sources.

This peak lasts only a few weeks. If birds arrive too late, they miss the moment when food is abundant for raising their chicks. Additionally, there is only a narrow time window for laying eggs, incubation and feeding the young before the cold returns. Any delay can mean the chicks won’t survive the migration south. “Birds are essentially breeding on a knife’s edge,” says Jesper Madsen.

Based on current climate trends, the team estimates that the observed flexibility in migration timing may help birds keep pace with spring for another 18 to 28 years. After that, faster migration alone may not be enough.
“These birds show remarkable adaptability,” says Hans Linssen from the University of Amsterdam. “But by mid-century, they may need to rely on other strategies – such as shifting their wintering areas or changing migration routes entirely – to avoid falling out of sync with the Arctic spring.”

Enabled by technology
The study was made possible by technological advances that allow researchers to track individual birds with high precision using GPS transmitters.

Lisa Vergin is enthusiastic:
“It has given us a completely new opportunity to follow tagged individuals year-round and into remote Arctic regions that are difficult for us to reach. We’re constantly getting new and surprising results.”

Read the article ‘Scope for waterfowl to speed up migration to a warming Arctic in Nature Climate Change.

For further information, please contact Professor and Head of the Center for Adaptive Nature Management, Jesper Madsen, Department of Ecoscience at Aarhus University, phone: +45 29440204 or email: jm@ecos.au.dk.