One of the scrubs best known residents is Florida's only endemic bird, the Florida scrub-jay. When walking through scrub areas, small scrub lizards often race off in the distance — perhaps an adaptation for crossing the hot sand quickly. Many animals of the scrub spend much of their lives underground to escape the hot Florida sun as well as to avoid predators. The gopher tortoise digs a burrow underground that may be up to ten feet deep and up to 30 feet long. More than 360 species may share the gopher's burrow. Other small animals such as the sand skink leave only "S"-shaped tracks as it "swims" just beneath the surface of the sand. It is the only known sand-swimming skink in North America and occurs in only seven counties in Florida.