Climate Change and Polar Bears: Unlikely to Survive on Land-Based Food

As climate change melts Arctic sea ice and forces polar bears onto steady shores, it seems that they will have to adapt to a new diet. However, it is highly unlikely that these animals will be able to survive strictly on land-based foods, according to a new study.

While dry land offers its own unique food choices - including berries, birds and eggs - this low-fat diet is not nearly as nutritional as the traditional, lipid-rich prey polar bears have an appetite for - ice seals.

"Although some polar bears may eat terrestrial foods, there is no evidence the behavior is widespread," lead author Dr. Karyn Rode said in a news release. "In the regions where terrestrial feeding by polar bears has been documented, polar bear body condition and survival rates have declined."

Not to mention that when hungry polar bears are hunting for seals in the water, they don't have much competition for food from other species. However, that's not the case on land. Grizzly bears share the same terrestrial habitats with polar bears, and are potential competitors for the already limited supply of land-based food. And as polar bears are increasingly displaced from their sea ice habitats, the odds of thriving on land appear grim.

"The smaller size and low population density of grizzly bears in the Arctic provides a clear indication of the nutritional limitations of onshore habitats for supporting large bodied polar bears in meaningful numbers," said Rode. "Grizzly bears and polar bears are likely to increasingly interact and potentially compete for terrestrial resources."

Polar bears are doing their best to stand up to climate change, taking matters into their own hands by shifting their distribution patterns towards icier areas further north. However, their valiant efforts may not be enough. These cold-climate mammals depend on sea ice to travel, hunt and mate, and in some areas den. But if the rate of climate change doesn't let up soon, these animals will be gone before 2100, experts say. Populations have already plummeted a whopping 40 percent in the last decade alone as severe ice loss - forcing polar bears to travel further to find food - leads to starvation. (Scroll to read on...)

And with Arctic sea ice expected to disappear entirely by the end of the century, polar bears are quickly realizing that it's either adapt or die. But even that may not be an option.

During the study, a team of scientists led by the US Geological Survey (USGS) found that terrestrial foods cannot compensate for the lack of fatty, delicious seals. Fewer than 30 individual polar bears have been observed consuming bird eggs from any one population, which typically range from 900 to 2,000 individuals.

"There has been a fair bit of publicity about polar bears consuming bird eggs. However, this behavior is not yet common, and is unlikely to have population-level impacts on trends in body condition and survival," Rode explained.

There aren't many foods as energetically dense as marine prey. Previous research has suggested that polar bears consume the highest lipid diet of any species because it provides all essential nutrients, and is ideal for maximizing fat deposition and minimizing energetic requirements. So switching to high-protein, low-fat animals and vegetation found on land is no doubt unsatisfying, and unlikely to help polar bears survive. They are not physiologically suited to digest plants, and it would be difficult for them to ingest the volumes that would be required to support their large body size.

"The reports of terrestrial feeding by polar bears provide important insights into the ecology of bears on land," Rode concluded. "In this paper, we tried to put those observations into a broader context. Focused research will help us determine whether terrestrial foods could contribute to polar bear nutrition despite the physiological and nutritional limitations and the low availability of most terrestrial food resources. However, the evidence thus far suggests that increased consumption of terrestrial foods by polar bears is unlikely to offset declines in body condition and survival resulting from sea ice loss."

The results were published in the journal Frontiers in Ecology and the Environment.

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