When activated, this ability temporarily grants you 30% of your maximum health for 20 sec while in Bear Form, Cat Form, or Dire Bear Form. After the effect expires, the health is lost.
Survival Instincts is a Druid talent in the Feral Combat tree. It's basically the druid form of Last Stand.
After patch 4.0.1, this talent now no longer increases your health by 30% of its maximum, but reduces all damage taken by 60%.