The American Crocodile (Crocodylus acutus) is also native to the region and has been designated as endangered since 1975. Unlike their relatives the alligators, crocodiles tend to thrive in brackish or salt-water habitats such as estuarine or marine coasts. Their most significant threat is disturbance by people. Too much contact with humans causes females to abandon their nests, and males in particular are often victims of vehicle collisions while roaming over large territories and attempting to cross U.S. 1 and Card Sound Road in the Florida Keys. There are an estimated 500 to 1,000 crocodiles in southern Florida.[45]