Polar bears, Ursus maritimus, typically hunt ringed and bearded seals hanging out near sea ice, but they’re opportunistic predators and scavengers too. They’ve been known to dine on at least seven species of whale, for example, when they get the chance. Well here’s something new: on a small fjord in Svalbard, Norway, an adult male polar bear was spotted preying on two white-beaked dolphins. This is the first time that the species has been known to fall prey to polar bears and, as you can see in the photograph above, he started to cover the remains with snow. It looks like he was trying to freeze his leftovers. The work is described in Polar Research this week.
In Raudfjorden on April 23, 2014, during an annual bear capture-recapture expedition, Norwegian Polar Institute’s Jon Aars and colleagues encountered a male polar bear with the carcass of a mostly intact white-beaked dolphin (Lagenorhynchus albirostris) on the sea ice about 5 meters from shore. It was only missing some of the fat layer on its dorsal side. Another dolphin – rather the spine, ribcage, and skull of a dolphin – was on land 50 meters south. Tracks in the snow indicated that the same polar bear fed on both.
About a meter away from the intact dolphin was a small hole covered with ice slush (pictured above). It appeared to be a breathing hole kept open by dolphins trapped in the ice. After all, the surrounding sea ice is 20 centimeters thick, and this was the only spot on the fjord without solid ice. White-beaked dolphins are frequent visitors to Norwegian High Arctic waters in the summer, but they don’t usually go so far north in early spring. That winter, however, the area was ice-free, and they were swimming in open ocean until strong northerly winds packed drift ice into the fjords from April 17 to 18, trapping the dolphins. They were likely killed when they surfaced for air.
No meat had been taken from the more-or-less intact dolphin yet, and when the team chanced upon him, the bear was in the process of covering it with snow. This probably keeps foxes, gulls, and other scavengers away, though caching is a rare behavior in polar bears. They typically digest the fat that they consume from carcasses within a day, so the time that they’d need to keep competitors away is brief.
"We think he caught the second dolphin because he could, and then had extra food later," Aars tells New Scientist. The bear was temporarily immobilized, and based on his teeth, he's 16 to 20 years old. And while his ribs were clearly showing, he did have a rather full belly.
At least seven white-beaked dolphin carcasses were spotted in or around the same area that summer and fall, and six different polar bears were seen scavenging on them. The photograph below shows an adult polar bear feeding on dolphin remains in Raudfjorden on July 2, 2014. Judging from the degree of decay, the dolphins likely came from the same pod that became trapped in ice that April.
Images: 2015 J. Aars et al. / Polar Research CC BY-NC 4.0
[h/t New Scientist]