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BiologyThe Nile crocodile shows a shift in diet with increasing body size. Young individuals usually feed on insects, small fish, amphibians and crustaceans, the diet changing to include more vertebrates, including fish, turtles, birds and mammals, as the individual matures (3) (6) (7). The largest Nile crocodiles are capable of taking prey up to the size of antelope, buffalo, zebras and wildebeest, dragging the prey into the water and spinning the body around to tear off chunks of flesh (2) (3). Like other reptiles, Nile crocodiles control body temperature by seeking shade when hot and basking in the sun when cool (6), and basking crocodiles are often a common sight along riverbanks. Nile crocodiles may also dig dens, which they use to retreat from adverse environmental conditions (3). These reptiles have quick reflexes and can be surprisingly fast runners on land (2) (6), though they may tire quickly (7). Breeding usually takes place during the dry season (6) (7), though the exact timing varies with location (3). Mating takes place in the water. The nest is a hole, up to 50 centimetres deep, dug by the female into a sandy bank, several metres from the water (2) (3) (6). The female Nile crocodile is an attentive parent, and, after laying up to around 60 eggs, will cover the nest with sand and guard it for the entire incubation period, around 90 days (2) (3) (4). Sex in the Nile crocodile is determined by the temperature at which the eggs are incubated, with females produced below 31 degrees Celsius, and males at above 31 to 34 degrees Celsius (8). When about to hatch, the young make a “peeping” noise, which encourages the female to excavate the nest. The female then gathers the hatchlings in her mouth and transports them to the water, where they remain in a group for several months, protected by the female (2) (4) (7). Amazingly, the Nile crocodile's powerful jaws can be used incredibly gently, and the female can even help hatchlings emerge by carefully rolling and squeezing the eggs in her mouth. However, despite this care and vigilance, nests may be raided by a variety of other animals, and hatchling crocodiles are very vulnerable to predation (3) (7). Young females reach sexual maturity at a body size of around 2.6 metres, and males at 2.7 to 3.1 metres (3) (9), achieved at around 12 to 15 years old (2). The Nile crocodile can be long-lived in the wild (6). The social behaviour of the Nile crocodile is often underestimated (3). Males are territorial, patrolling and defending territories which may encompass a length of shoreline and extend up to 50 metres out into the water (4). Co-operative feeding behaviour has also been reported. For example, several animals may cordon off an area of water to concentrate fish within it, and dominance hierarchies determine the order in which individuals feed (3).