Barnacle geese are shifting their migratory patterns northward in response to global heating, new research has found, in a stark indication of how wildlife is being affected by the changes in climate.
In their spring journey from the UK to their breeding grounds on Svalbard, one population of the geese has been forsaking a traditional feeding stop in Norway’s Helgeland, south of the Arctic circle, in favour of a stop further north in Vesterålen, far into the Arctic circle.
The move has happened as spring has come earlier to the region. Over the period studied, from 1975 to 2017, the onset of grass growth in Vesterålen has come sooner by about half a day each year, making a big difference in the availability of food for the birds.
Significantly, younger birds have been quicker to make the switch. The study follows other research which has found bird species migrating earlier, land-based wildlife moving their habitats, and fish shifting polewards in response to climate change.
This is the first to show migratory animals learning new routes, with individuals changing from old migration routes that they learned earlier in life in favour of the new routes, which are then transmitted to others – for instance, by offspring following their parents.
The study, published in Global Change Biology, analysed 45 years of observations by the Norwegian Institute for Nature Research, the University of St Andrews in Scotland, the University of Groningen in the Netherlands, BirdLife Norway and the British Waterfowl and Wetlands Trust.
In the case of these geese, the effects of the change appear to have been mostly benign, as the amount of digestible biomass available for them increased and the population studied roughly doubled in size in the past quarter century.
However, the shift has opened them up to an unexpected new danger from climate change: predation from polar bears, which have started to rely on eating bird eggs now that the ice floes from which they used to hunt seals are disappearing.
“[The geese] have an amazing capacity to react to climate change, and actually adjusted very fast,” said Thomas Oudman, of the school of biology at St Andrews, co-author of the study. “This was only possible because alternative feeding areas have become available, also because of climate change.
For many other species, this might not be the case, [so] climate change might threaten their existence. Other migratory animals, particularly less social ones, may be less capable of finding and colonising newly available areas.”
Many other birds, for instance, have few or no viable alternative areas to visit, he noted, or may find it harder to transmit new routes to offspring.
“There are many bird [species] that appear to be in trouble,” he told the Guardian. “That’s why we are trying to find out how birds develop their migratory behaviour, and how changes come about. We have found a clue in geese, showing that they can change routes during their life, especially young geese. But this change is probably speeded up by the fact that geese travel in groups. This points at the possibility that individually migrating birds are generally more vulnerable to climate change, especially those that rely on very specific feeding areas, such as many shorebirds that rely on intertidal areas.”