Rattlesnakes are venomous snakes that form the genera Crotalus and Sistrurus of the subfamily Crotalinae (the pit vipers). Rattlesnakes are predators that live in a wide array of habitats, hunting small animals such as birds and rodents. Rattlesnakes receive their name from the rattle located at the end of their tails, which makes a loud rattling noise when vibrated that deters predators. Rattlesnakes are the leading contributor to snakebite injuries in North America, but rarely bite unless provoked or threatened; if treated promptly, the bites are seldom fatal. The 36 known species of rattlesnakes have between 65 and 70 subspecies, all native to the Americas, ranging from central Argentina to southern Canada. The largest rattlesnake, the eastern diamondback, can measure up to 2.4 m (7.9 ft) in length. Rattlesnakes are preyed upon by hawks, weasels, kingsnakes, and a variety of other species. Rattlesnakes are heavily preyed upon as neonates, while they are still weak and immature. Large numbers of rattlesnakes are killed by humans. Rattlesnake populations in many areas are severely threatened by habitat destruction, poaching, and extermination campaigns.