be female. Males can only be born if the temperature is within that narrow range. The hatchlings start to make a high-pitched chirping noise before hatching, which is the signal for the mother to rip open the nest. It is thought to be either difficult or impossible for hatchlings to escape the nest burrow without assistance, as the surface may become very heavy and packed above them. The mother crocodile may pick up the eggs in her mouth, and roll them between their tongue and the upper palate to help crack the shell and release her offspring. Once the eggs hatch, the female may lead the hatchlings to water, or even carry them there in her mouth, as female American alligators have been observed doing. Hatchling Nile crocodiles are between long at first and weigh around . The hatchlings grow approximately that length each year for the first several years. The new mother will protect her offspring for up to two years, and if there are multiple nests in the same area, the mothers may form a crèche. During this time, the mothers may pick up their offspring either in their mouths or gular fold (throat pouch) to keep the babies safe. The mother will sometimes carry her young on her back to avoid natural predators of the small crocodiles, which can be surprisingly bold even with the mother around. Nile crocodiles of under two years are much more rarely observed than larger specimens, and more seldom seen than the same age young in several other types of crocodilian. Young crocodiles are shy and evasive due to the formidable array of predators that they must face in sub-Saharan Africa, spending little time sunning and moving about nocturnally whenever possible. Crocodiles two years old and younger may spend a surprising amount of time on land, as evidenced by the range of terrestrial insects found in their stomachs, and their lifestyle may resemble that of a semi-aquatic mid-sized lizard more so than the very aquatic lives of older crocodiles. At the end of the two years, the hatchlings will be about long, and will naturally depart the nest area, avoiding the territories of older and larger crocodiles. After this stage, crocodiles may loosely associate with similarly sized crocodiles and many enter feeding congregations of crocodiles once they attain , at which size predators and cannibal crocodiles become much less of a concern.