A hungry polar bear (Ursus maritimus) will eat just about anything. Oh sure, they prefer to dine on nice fatty seals (I mean, what Arctic creature wouldn’t?), but when push comes to shove they’ll eat caribou, walruses, nuts, birds, and even stinky, rotten whale carcasses.
Oh yeah, they’ll also eat eggs. Research over the past few years has documented polar bears increasingly munching on goose eggs, which are sometimes the only readily available source of nourishment when the ursines are stuck on land after their normal sea-ice habitats have melted (you know, from climate change).
Eggs are, of course, yummy but they come with an ecological cost. According to a paper published this week in Frontiers in Ecology and Evolution, polar bears in some areas are eating so many eggs that bird populations soon suffer.
The research—by a team of 16 international scientists—was conducted in east Greenland and the Norwegian island Spitsbergen, part of the Svalbard archipelago, between 2004 and 2014. At each of five sites studied, the sea ice season lasted fewer days each year. As a result, polar bears spent a lot more time on land: 15 percent more time each year of this century.
Unfortunately, the ice season also started earlier each year, by as much as 3 days in some sites. That gave polar bears access to the land at the same time as the key nesting seasons for several sea birds, including barnacle geese (Branta leucopsis), common eiders (Somateria mollissima) and glaucous gulls (Larus hyperboreus). Guess what happened next?
Yup, the hungry polar bears went to town on those nests. In the years when bears made landfall well before the eggs started hatching, they ate more than 90 percent of the eggs. That’s enough to have a potentially devastating effect on future populations.
None of those birds are endangered—they’re all classified as “least concern” on the IUCN Red List and each species nests in plenty of other sites. Still, this shift in bear eating patterns bodes poorly for the birds’ ability to nest in those traditional sites.
Obviously this is a somewhat limited study. These five sites weren’t exactly swarming with polar bears or birds, but the observations in this study match up with similar studies in Canada, where polar bears have also been observed eating goose eggs to replace unreachable seals. As Polar Bears International’s chief scientist, Steven Amstrup, told me a few years ago, “If the whole bear population was trying to survive on eggs, soon there would be no geese left.”
And if that backup source of food disappears, what happens to polar bears then?
Photo: Greenland Travel. Used under Creative Commons license