The saltwater crocodile is a powerful and opportunistic predator, feeding on a wide variety of prey. Juveniles take smaller items such as insects, amphibians, crustaceans and fish, while adults also take reptiles, birds and mammals. The largest individuals occasionally take much larger prey such as dingoes, wallabies, domestic animals, and even humans, and will sometimes eat carrion (2) (3) (7) (8) (9). Stones and pebbles may also be ingested, to help grind food in the stomach (8). Where the range of the saltwater crocodile overlaps with that of the Australian freshwater crocodile, Crocodylus johnstoni, the saltwater crocodile outcompetes and sometimes kills the latter (3).
The saltwater crocodile breeds in the wet season, with courtship occurring in northern Australia between September and October, and nesting between November and March. Breeding territories are usually established along tidal rivers or freshwater areas, the female choosing a nesting site near water. The nest itself is a mound, around 175 centimetres long and 53 centimetres high, constructed from vegetation and mud, into which the female lays around 40 to 60, or sometimes up to 90, eggs. The female guards the nest during the 80 to 98 day incubation period, although eggs are sometimes lost to predators, and entire nests are often lost to flooding (2) (3) (5) (8) (10). The hatchlings measure around 29 centimetres (8) and, like all crocodilians, the sex is determined by the incubation temperature, with low temperatures producing mainly females, and higher temperatures mainly males (2) (3) (6) (8).
Crocodilians show a remarkable level of maternal care, the female excavating the nest in response to calls from the hatchlings, and even gently rolling eggs in the mouth to assist hatching. The female will then carry the hatchlings to water, and remain with the young for several months. Despite this level of care, only an estimated one percent of all young reach maturity, being vulnerable to a range of predators and even to cannibalism by adults (2) (3) (6) (8). The young start to disperse at about eight months, and territorial behaviour begins at about 2.5 years (7), although breeding does not usually begin until about 12 to 14 years in females (at a length of around 2.1 to 2.5 metres), and 16 to 17 years (at 3.1 to 3.3 metres) in males (2) (3) (7) (8). Like other crocodilians (6), the saltwater crocodile is potentially long-lived, surviving to over 65, or perhaps even to over 100 years (7) (8).