The Arctic marine regions of Svalbard, Greenland and eastern Canada provide a rich summer table and breeding opportunities for numerous seabird species. In winter, however, most of the birds migrate to the North Atlantic and often remain on the open sea. There they are exposed to wind and waves and often after big storms numerous dead birds are washed up on beaches. An international research team led by France investigated whether storms, which could become more frequent and violent due to climate change, could be the cause of mass mortality and came to a different conclusion.
Puffins, Brunnich’s and common guillemots, little auks and kittiwakes do not appear to die directly as a result of winter storms, according to model calculations in the published study with Manon Clairbaux, postdoctoral researcher at France’s CEFE and now at the University of Cork (IRL) as lead author. The authors suspect that the birds tend to find not enough food after the storms because the water layers have been stirred up, causing crustaceans and small fish to either drift into deeper water layers or the swarms and schools to be torn apart. As a result, the seabirds would not gain enough energy to survive the cold and subsequent storms.
The seabird species studied by the research team spend their summers in the Arctic coastal regions and migrate to the North Atlantic in autumn, where no sea ice blocks their feeding grounds. But their areas are often at the centre of strong winter storms, as the international research team was able to show. They mapped the wintering locations of about 1,500 birds of the above five species and compared them with data on winter storms in four different strength classes. This showed that Brunnich’s guillemots, for example, experience up to four category 4 (out of 4) storms per month in winter. This exposes the animals to massive swells, strong winds and precipitation, and very low water and air temperatures. Since all alcids are rather heavily built to be able to dive energy-saving and this goes at expense of the flying, it was assumed so far that the animals, if on the open sea, sit out the storms and use too much energy on that occasion and therefore die. But Clairbaux and her colleagues calculated that the animals could normally withstand the environmental conditions from the energy side. But a prerequisite for this is enough food.
According to the researchers, the answer for the numerous dead birds lies more in the food. The storms stir up the water layers considerably and the number of crustaceans and fish is greatly reduced. According to the team’s calculations, depending on the species, the birds can go without food for between two and eight days in autumn and two and six days in winter, depending on the temperature. So when food is lacking after severe storms, it becomes critical for the birds. But the researchers explain in their paper, published in the journal Current Biology, that their findings should be viewed with caution. This is because their modelling of the energy expenditure of the birds studied and the possible energy losses due to environmental conditions in the storms is rather conservative. On the one hand, it was hardly possible to obtain true-to-life data on the energy expenditure and behaviour of birds during storms; on the other hand, only air and water temperatures, wind speeds and the assumption of reduced activity due to heat loss and increased energy expenditure were included in the models, as the data situation was insufficient for other factors.
The seabird species included in this study have been under pressure for some time. In addition to fishing, pollution of the oceans and breeding grounds and a reduced food supply due to changing climatic conditions have caused some populations, such as puffins, to decline sharply. As climate change is expected to result in more extreme meteorological events (as we have experienced ourselves), the number and intensity of storms in wintering areas could increase. While the adverse conditions that already exist there don’t seem to bother the bird species much, and there seems to be a sort of balance between pros and cons. But the balance could quickly tip not in the birds’ favor, pushing them over the edge from which there will be no coming back.
Dr Michael Wenger, PolarJournal
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