The advantages for animals migrating to northern breeding grounds are being eroded, as the animals experience lower food availability, higher pathogen pressure and increased predation rates.
The dunlin (Calidris alpina) is a small, migratory wader. Photo: Brett Sandercock / NINA.
Every year, millions of wild animals undertake long-distance migration to breed in the north. Migration is both dangerous and resource demanding, but the advantages outweigh the disadvantages. High food availability and long days for foraging in the summer, lower pathogen and parasite pressure and fewer predators represent major benefits, making the risk worthwhile. However, the advantages of migrating to northern latitudes are decreasing.
“Animals in the northern regions are experiencing changes in food supply related to climate change, and diseases and parasites are spreading north, as well as predators”, says Brett Sandercock, senior scientist in the Norwegian institute for nature research (NINA).
In collaboration with colleagues from The Czech Republic, Hungary and Great Britain, the international team have summarized research on a broad spectrum of migrating animals. The research has been published as a new article “Animal migration to northern latitudes: environmental changes and increasing threats” in “Trends in Ecology & Evolution”.
Hungry bears and tiny microbes threaten the common eider
The common eider is one of the species facing difficulties on their migrations for their northern breeding grounds, such as Svalbard. Polar bears have a harder time hunting seals due to the decreasing sea ice, and instead turn to the nests of common eider and other colonial species for food.
In Arctic regions of Canada, the common eider is facing yet another large – and tiny – challenge. Climate changes have opened up new areas in the north for pathogens and parasites, and recent outbreaks of avian cholera have killed large numbers of birds in some colonies.
Disturbances in the “undisturbed” north
Changes along the migratory routes, especially land use changes and anthropogenic disturbances, have received most attention as explanations for the decline in numbers of many populations of migratory animals.
“Changes in the northern regions have received less attention, as these regions are often seen as large, undisturbed regions. There are, however, many changes occurring in these more remote areas", Sandercock says.
Both acute and long-term stressors affect migrating animals
“The spatial and temporal extent of the changes are important factors in order to be able to forecast the effect of the changes”, says Sandercock.
Disturbances, such as storms, or a temporary mismatch in the timing of food resources, can be relatively brief, acute stressors that do not necessarily affect the animals over the long term. If repeated, however, such acute events can turn into long-term stressors. In Alaska, for example, the insects that the sandpipers rely on for food emerge six days too early, on average, resulting in food shortages when young birds need the food the most. Another example is the wild reindeer at Svalbard. Rain on snow events during the winter result in a layer of ice covering the vegetation, making it inaccessible for the reindeer.
Long-term, chronic stressors, such as temperature increase or an increase in woody plants, are slow, gradual changes over several decades. When such changes reach an ecological threshold, the whole ecosystem might shift to such an extent that it is no longer suitable for some of the species using the areas.
Need for international solutions
It will be challenging to directly mitigate the large-scale impacts of climate change for migratory species that are dependent on multiple environments distributed across several regions of the globe. Conservation efforts both on small and large scales are necessary, from local nest protection to development of networks of protected areas.
“It is important to consider the cumulative effects of all the different factors in different areas, and international solutions are necessary to mitigate the negative effects”, says Sandercock.
Brett Sandercock (NINA)
Lead author Vojtech Kubelka