The geographic range which the tuatara inhabits is a difficult niche for any species, particularly a reptile. The islands are generally cliff-bound, frequently exposed to strong winds, and support a natural, often stunted, vegetation of salt and wind tolerant species. Most islands are also home to several species of sea birds, whose nutrient-rich guano helps support the island's ecosystem. The habitat is cold and damp, with temperatures rarely exceeding 70 degrees Fahrenheit, and a humidity level of about 80 percent. The temperature may often approach freezing, but the tuatara is able to maintain normal activities at temperatures as low as 45 degrees Fahrenheit. Preferred body temperature is between 60 and 70 degrees, this is the lowest optimal body temperature of all reptiles. At temperatures above 76 degrees, tuataras show signs of distress, and most will die if the temperature exceeds 82 degrees.