Five basic criteria are used to determine if a species is threatened or endangered.
You've probably heard that global warming in the Arctic is killing off polar bears by shrinking their habitat, but are other arctic animals suffering, too?
When you've been to the zoo have you noticed how some of the animals pace around a lot? "Born to Roam" on this Moment of Science.
Eating snow to obtain water is metabolically expensive–it would take too much energy to melt down enough snow. Consequently, polar bears have evolved so that they don’t need to drink free water.