Ice is disappearing. Every summer the remaining ice is getting smaller making food scarce. The polar bears are also forced to swim longer and farther in open ocean water. Some of the bears, particularly cubs do not survive. Those that do come ashore thinner.
Sea ice now is melting earlier in spring and forming later in autumn. This forces the bears to spend longer periods without food and is causing their health to decline.
Polar bears are hungry bears. Since they do not have all the ice and seal hunting they will look for food wherever they can.