Arctic geese adapt by finding a new migratory route

Temperatures are rising faster in the Arctic than the global average, and this is affecting seasonal patterns of behavior in many species of animals. For migratory species that breed in the Arctic during summer, this is especially significant since the timing of migration, arrival and breeding is critical. Add to this the fact that migratory species may be experiencing increased anthropogenic pressures along their travel routes, and it becomes clear that times are very challenging for these animals. 

Species may respond by changing the timing of their migration and breeding, by extending their breeding range or altering their migration route. Some migratory species may remain to breed in traditional wintering areas, while others end up becoming vagrants in response to climate change. Mostly, these processes of adaptation take time to become established but a new study on pink-footed geese (Anser brachyrhynchus) has recorded a relatively rapid adjustment of behavior in response to climate change.

Traditionally, pink-footed geese breed in Svalbard in summer and then migrate southwards, via a narrow corridor along the west coast of Norway, to their wintering grounds in western Denmark, the Netherlands and Belgium. However, many pressures and disturbances along this flyway over the past decades have made it less and less attractive to the geese. These include organized scaring by farmers at key stopover sites, agricultural crop changes and new hunting regulations that allow more geese to be harvested. 

In a new study, published in the journal Current Biology, researchers suggest that in response to these anthropogenic pressures, pink-footed geese have found a new migration route and breeding location which is almost 1,000 kilometers away from their original summer stomping grounds in Svalbard. Each year, more and more geese join the individuals flying to the new summer grounds, including geese of other species. The new population of pink-footed geese now numbers over 4,000 individuals.

“It is extremely fascinating to witness such rapid evolution of new breeding grounds and migratory route by a bird species that is regarded as being very traditional in its behavior and site use,” said Jesper Madsen of Aarhus University in Denmark. “It gives some hope for ‘ecological rescue’ at times of very radical environmental changes due to climate change and, more broadly, global change.”

“We observe a new distinct population of birds in the making, in real time,” he added. “This is very rare to observe. The speed of the development is astonishing.”

Madsen’s team has been studying Norway’s Svalbard population of pink-footed geese for more than 35 years. They’ve kept tabs on the population size and demographic variables, using a systematic marking and resighting program. About 20 years ago, they started getting reports of geese turning up on migration in Sweden and Finland, which were confirmed as members of the Svalbard population.

This long-term population monitoring and Capture-Mark-Recapture (CMR) program has enabled the researchers to follow the establishment of the new migration route from an early phase. In the 1990s, single individuals or small flocks of pink-footed geese were reported by the goose counting networks in southern Sweden during autumn and spring, and in western Finland during spring. Since the early 2000s, however, observations of flocks have become more regular and numbers have increased in both countries. 

The new route takes birds from the wintering grounds in western Denmark, the Netherlands and Belgium, via the west coast of Finland, to new breeding grounds on Novaya Zemlya, an archipelago in the Arctic Ocean off the coast of Russia. As part of the monitoring program, some birds are fitted with marked neckbands and some with GPS tags, enabling scientists to map the locations of birds and even document nesting behavior in the new breeding areas. 

“It was a real surprise to see that half of the marked individuals in Oulu [Finland] migrated northeast to Novaya Zemlya in north Russia,” said Madsen. “From the tagging information we could not only follow their new path but also got indications that females were breeding there. This site is around 1,000 kilometers east of the traditional Svalbard breeding grounds.

“It was also cool to observe that geese from the traditional flyway have turned up on the new route and seemed to have switched. Hence, social learning and following individuals from the new route has been an important phenomenon, which also explains how this development could be so fast.”

In their report, the researchers detail the abrupt formation of the new migration route and population of pink-footed geese over the course of 10 to 15 years. The population has grown over time due to successful breeding and high survival rates, combined with continued immigration of geese from the old route to the new one.

This development has only been possible due to the fact that rising temperatures have made the environment in Novaya Zemlya suitable for geese to inhabit in summer. While the new population is not genetically or demographically isolated yet, the researchers note that it does already qualify as a separate population. The researchers suggest that cultural transmission has enabled the species to colonize a new breeding area rapidly, and to establish a totally new migratory route, including new stopover and wintering sites. 

The new route does have some disadvantages, Madsen says. For instance, it’s longer. But the researchers suspect the benefits of the new route and breeding grounds outweigh any downsides. The findings in geese show the importance of social learning when it comes to adapting to a changing planet, Madsen notes, especially in social animals, including birds but perhaps also in hoofed ungulates, wolves, and whales.

“At this time, when climate change and other human activities threaten many species, not least the Arctic ones, social learning can be a behavior that can provide advantages to avoid some negative impacts, at least in the short term,” said Madsen.

The researchers say they hope one day to observe the geese in their new breeding grounds in Russia. For now, they’ll keep an eye on the future development of the new population using GPS-tracking devices and remote sensing of the new environment.

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By Alison Bosman, Earth.com Staff Writer

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