Climate Change Is Changing Kodiak Bears’ Diets

30 Aug

Kodiak bears typically feast on sockeye salmon during the summer. But climate change has changed the bears' eating habits.

Typically, Kodiak bears eat salmon during the summer, but climate change is changing their diet. Photo: Shutterstock

There’s no more iconic a predator-prey relationship than that of bears and salmon.

Typically, brown bears on Kodiak Island in Alaska feed on sockeye salmon as they swim upstream to spawn. But things are different these days.

Red elderberries, another integral part of the Kodiak bears’ diet, are ripening earlier thanks to warmer climates. Now that salmon and elderberries are available to the bears at the same time, they’re choosing to chow down on the red elderberries and leave the salmon to die in the streams.

Researchers from Oregon State University, University of Montana’s Flathead Lake Biological Station, and Kodiak National Wildlife Refuge recently published a paper about their observations. Typically, they write, the Kodiak bears gorge on sockeye salmon in the summer, but in 2014, researchers noticed the streams in the Kodiak National Wildlife Refuge were full of salmon, and no bears were to be found. This happened again in 2015.

“Prior to that summer, we found streams that were littered with thousands of shredded salmon carcasses,” said study lead author Will Deacy, a postgrad student at Oregon State University. “In 2014, and again in ’15, we were stunned to find such a strikingly different scene. There were piles of rotting, intact carcasses that had died after spawning instead of being killed by bears.”

The researchers found the bears on the hillsides feeding on red elderberries. Typically, wild elderberries don’t ripen before late August or early September, and bears feast on the salmon until berry season. But due to warm spring temperatures on Kodiak Island, the berries were ripening weeks earlier—at the same time as the peak of the salmon migration.

2014 was one of the warmest years on Kodiak Island since record-keeping began around 1960. Scientists say that although there is significant variation in Kodiak’s climate, the warming trend is likely to continue.

“As climate change reschedules ecosystems, species that were once separated in time are now getting a chance to interact—in this case, the berries, bears, and salmon,” said OSU ecologist Jonny Armstrong, a member of the research team. “This is going to have large impacts that are hard to predict.”

Just to give one example, birds that rely on Kodiak bears pulling salmon out of the stream could find themselves without vital nutrition. It could also change bear demographics due to diet change.

“These bears eat dozens of different foods throughout the year, but now two of them are overlapping. This is causing a disruption in the food web that could have profound implications for the ecology of the island,” Deacy said.

“This overlap in their resources forces the bears to make a choice that could in the long run result in fewer bears and/or unexpected changes in ecosystem structure,” said study co-author Jack Stanford of the University of Montana.

Kodiak bears are not the only species being affected by climate change, and it’s hard to predict the exact consequences of the changes in seasonal availability of fruit. It will be interesting to see if this phenomenon continues and how it affects bear populations on Kodiak Island.

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