Polar bears will hardly withstand increasingly longer Arctic summers. These periods force them to spend more time on land, where they are unlikely to be able to adapt to these conditions and will even risk dying of starvation, according to a new study published in Nature Communications.
The researchers reached this conclusion after observing twenty polar bears for three summer weeks. They tried different strategies to maintain energy reserves, including resting, scavenging, and foraging. However, almost all of them lost weight quickly: on average, about a kilo a day.
"None of the strategies will allow polar bears to exist on land beyond a certain period of time. Even the bears that foraged lost body weight at the same rate as those that lay down," explains the director of the Bear Center of Washington State University and study co-author Charles Robbins.
Until now, little was known about the energy expenditure and behavior of polar bears when confined to land. And researchers used collars with video cameras and GPS to track what polar bears summering in the western Hudson Bay region of Manitoba, Canada did and ate.
During the Arctic summers, these animals cannot turn to their favorite prey, seals. However, climate change has prolonged the period they spend outside. A more important problem than initially believed, according to researchers.
Many of the adult male polar bears simply lay down to conserve energy, burning calories at a rate similar to hibernation. Others actively foraged and consumed bird and caribou carcasses, as well as berries, seaweed, and grasses. Some adult females spent up to half their time searching for food. However, all that activity did not bear fruit.
"Terrestrial foods gave them some energetic benefit, but ultimately the bears had to expend more energy to access those resources," the researchers note.
The data obtained (loss of one kilo per day) are not encouraging. And they put their survival at risk. "As they are forced to come ashore sooner, the period in which they normally acquire most of the energy they need to survive is reduced. With increased land use, the expectation is that we will likely see an increase in famine "Robbins says.
