Polar bears are perfectly adapted to their harsh environment, even in energy terms. Summer time, when all other animals are flourishing, means fasting for polar bears and the king of the Arctic has live off its energy reserves gained during the winter time. However, thanks to climate change, summer are getting longer and the animals weaker.

 Polar bears go hungry during the summer months, if the miss the moment to get on to the pack ice. If they cannot find proper food, they also feed on algae. Picture: Michael WengerPolar bears go hungry during the summer months, if the miss the moment to get on to the pack ice. If they cannot find proper food, they also feed on algae. Picture: Michael Wenger
Polar bears go hungry during the summer months, if the miss the moment to get on to the pack ice. If they cannot find proper food, they also feed on algae. Picture: Michael WengerPolar bears go hungry during the summer months, if the miss the moment to get on to the pack ice. If they cannot find proper food, they also feed on algae. Picture: Michael Wenger

Polar bears are used to go hungry for a longer period of time during summer season when the ice melts and their habitat shrinks. They are simply turning down their energy demand. However, their saving possibilities are limited according to a study by US scientists. The results of their work has been published in the journal Science. If the ice starts melting earlier in the season due to climate change and the summer fasting times become even longer, polar bear survival is threatened. The main food source of polar bears are seals hunted on the pack ice. Their main hunting season is between April and July which is the main breeding season of seals. From August onwards, the hunting success becomes lower because the seals go into the water and the sea ice retreats further north. Some polar bears manage to follow the ice, others stay on the shore and wait for the ice to come back.

During the summer months, seals are abundant on the ice edge. This is the place to be for polar bears if they want to feed on seals. Nevertheless, only every tenth to twelfth hunting chance is successful. Picture: Michael Wenger
During the summer months, seals are abundant on the ice edge. This is the place to be for polar bears if they want to feed on seals. Nevertheless, only every tenth to twelfth hunting chance is successful. Picture: Michael Wenger

Until now, some scientists assumed that polar bears can reduce their metabolism during this fasting time, just like animals in hibernation, and only move a little to improve their survival rate. This was called “walking hibernation”. This way, they could have lived through longer periods of fasting due to climate change. However, this “walking hibernation” theory did not coincide with the data measured by the researchers of the current study. Their results corresponded more with fasting, non-hibernating mammals. Albeit, the scientists also found out that polar bears can regulate their body temperature independently in different parts of their body. For example, they cool down their outer tissues while swimming long distances in order to keep their internal parts warm. “This regional heterothermy may represent an adaption to long-distance swims, although its limits remain unknown”, wrote the scientists. They noted a female polar bear which swam for nine consecutive days. Apparently, it had lost 22 percent of her body mass as well as her cub.

Mother bears are especially endangered during summer because they have to look after themselves as well as their cubs. Thus, reaching the pack ice as early as possible is important to them and should not be missed. Picture: Michael Wenger
Mother bears are especially endangered during summer because they have to look after themselves as well as their cubs. Thus, reaching the pack ice as early as possible is important to them and should not be missed. Picture: Michael Wenger

The results of the study clearly show that bears are unlikely to avoid a deleterious decline of their body condition that are expected with continued ice loss and lengthening of the ice-melt period. According to Steven Amstrup, chief scientist at Polar Bears International and co-author of the study, the work highlights the “extensive knowledge of polar bear ecology and corroborates previous findings that the key to polar bear conservation is arresting the decline of their sea ice habitat.”

 

Source: Anja Garms, Die Welt, www.welt.de