The key to your question is 'part of the year'. Polar bears naturally feed on seals and need the ice pack for their hunting grounds. The polar bears wait by a breathing hole until the seal pokes its head up then pounces. The polar bears also travel on the open ocean by moving from ice berg to iceberg looking for food.

Polar bears do survive by scavenging but that is not the best diet for them.So unless there is a steady diet of seals, bringing them strictly onto a land based habitat is not a good option.