According to one app for nature observers, it's the most commonly seen creature in California: the western fence lizard. Why?

For over 25 years, the endangered Mount Graham red squirrel has been quietly battling population decline atop one of ...

Four critically-endangered Western Santa Cruz Galapagos tortoise babies made their debut at the Philadelphia Zoo on Wednesday, April 23.

Video footage shows the goose and the tiger, named Vera, engaged in an intense face-off during which the bird managed to ward off the predator.

It took nearly 100 years for a duo of endangered Philadelphia Zoo tortoises to become parents -- the time to name those hatchlings will be much, much shorter.

It is hard to tell the girls apart, so zookeepers put a little dot of different color nail polish on each of them.