Polar bears thrive on the sea ice of the Arctic, where they prey primarily on the ringed seals that nervously look around for signs of trouble whenever they haul themselves out of the water.
But, as anyone who has spent any time observing them in the wild will confirm, polar bears are also extremely smart animals, and researchers have recently witnessed signs of remarkable adaptability in the face of a changing climate.
As Discovery News reported in April, researchers in Canada have observed several instances in which solitary bears have come ashore from the sea ice and wandered through snow goose colonies, eating eggs out of the nests, and even climbed rock cliffs to eat murre eggs and chicks.
In years past, by the time sea ice melted for the summer and polar bears came ashore, the eggs would have hatched and the birds flown the nest. However, as the climate warms, sea ice will melt, and bears will come ashore, earlier in the year.
What was particularly notable was that, in three quarters of the episodes that scientists witnessed, a solitary bear ate every single egg in the colony. That suggested the ramifications of this behavior for bird populations could be catastrophic. However, a new study by researchers affiliated with the American Museum of Natural History suggests that snow geese, at least, should be able to breathe easily.
Writing in a recent edition of the journal Oikos, the researchers describe running computer models that simulated the timing of events during the Arctic spring: the break-up of sea ice, the movement of bears onto shore, the migration of geese to the North, and the laying of eggs.
They found that climate change will indeed result in increased overlap between polar bears coming ashore and eggs being in the nests; that this overlap will indeed provide an opportunity for at least some polar bears to procure at least some food; and that the consequences will almost certainly result in a decline in snow goose numbers.
However, climate change will also cause increased variability from year to year, and as a result, there will be some years when there is no overlap at all — either because the geese have fledged earlier, the bears have come ashore later, or both. Those periodic years of “mismatch” will, they conclude, enable snow goose numbers to rebound again.
“Even if the bears eat every egg during each year of complete ‘match,’ our model shows that periodic years of mismatch will provide windows of successful goose reproduction that will partially offset predation effects,” said lead author Robert Rockwell, a research associate in the Division of Vertebrate Zoology at the Museum and a professor at the City University of New York.
Alas, this doesn’t mean that the future is bright for polar bears after all. The energy derived from wandering through snow goose colonies and chowing down on eggs is insignificant compared to an extra few weeks on the ice devouring seals. The evidence continues to point to polar bear numbers diminishing gradually as sea ice season shortens, and then precipitously once sea ice declines past a certain point.
Photo by Ansgar Walk, via Wikimedia Commons.