They're two of the world's most loved animals - but there's little love between them.
Jon Aars of the Norwegian Polar Institute and his colleagues have made the first ever observations of polar bears eating white-beaked dolphins that had ventured too far north – in fact, they saw this happen several times last year.
The first incident was in late April 2014. Collecting data in Svalbard, Norway, Aars's team stumbled across a bear with two dead white-beaked dolphins, a species no one had ever seen the bears preying upon before.
"We think the bear killed them, [using] a similar technique as killing seals," says Aars. He thinks it probably caught the two dolphins when, trapped below the sea ice, they found a small hole and surfaced for air.
The bear, pictured below, had already eaten most of the first dolphin but couldn't finish all of its catch in one sitting. So it made use of the natural freezer, storing a second dolphin – still largely intact – under the snow for a later snack, presumably.
Hiding leftover food is a rare behaviour in polar bears. "We think he caught the second dolphin because he could, and then had extra food later," says Aars.
Subsequently, the team came across at least five other polar bears feeding on dead dolphins in the same area.
"We were surprised as dolphins have not been reported in that area before," says Aars. The explanation could be that the Svalbard waters were unusually warm at the time, and that a pod of dolphins had become trapped there when strong northerly winds had pushed them out of open water and in among the ice.
Ian Stirling of the University of Alberta in Canada is not surprised that the bears decided to feast on dolphin meat: polar bears are known to be opportunistic predators, and have been recorded eating many different animals.
"They will eat any marine mammal given a chance," he says. "The bigger surprise was that the dolphins were entrapped before they could migrate south for the winter."
As the climate warms, Stirling believes the sight of polar bears tucking into weird meals could become more common. Polar bears are "willing to take and use anything possible when available", he says.
Journal reference: Polar Research, DOI: 10.3402/polar.v34.26612
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