Saltwater crocodiles have changed their diet from fish to pigs and it could be why their numbers have rapidly climbed in northern Australia, scientists say.

April 27, 2022

Saltwater crocodiles have changed their diet from seafood to mammals, and they’re moving inland to feed on their favourite tucker, a new study has found.

Feral pigs and buffalo are now on the apex predator’s menu, replacing fish, sharks and turtles, Charles Darwin University researchers say.

The diet change could be contributing to the massive reptiles’ increased movement into northern Australia floodplains, where feral pigs are abundant.

“We were surprised to observe such a significant shift in the diet of estuarine crocodiles across the Top End over the past 50 years,” ecologist Mariana Campbell said on Wednesday.

“Our results show that they have shifted from a marine-estuarine based diet, such as fish, marine turtles, to a more terrestrial-based diet of feral pigs, and buffalo.”

Researchers compared stable isotopes from museum bone specimens collected when crocodile populations were low, to the isotopes in bones collected recently.

They discovered that the isotopes prominent in crocodiles from five decades ago when the ambush predator’s diet was mainly marine-based were less significant in modern crocodiles.

The finding could also explain why crocodile numbers in the Northern Territory have recovered so quickly after the reptile, prized for its skins, was almost hunted to extinction in the 1970s before becoming a protected species.

There are now estimated to be about 100,000 adult crocodiles in the wild in NT, with another 30,000 in Queensland.

Dr Campbell said the increased availability of feral pigs in freshwater floodplains likely contributed to the success.

“A reduction in estuarine prey may have also contributed to the crocodiles’ diet change,” she said.

“It is likely a combination of a change in available prey and a general ingress of crocodiles from the estuaries into the freshwater flood plains.”

Saltwater or estuarine crocodiles, known as “salties”, are found in a wide range of habitats, including rivers, estuaries, creeks, swamps, lagoons and billabongs, according to the Australian Museum.

They mostly hunt at night and despite their dietary preferences changing, will eat just about any animal they can catch and overpower, including smaller crocodiles.

Small prey is crushed by the predators powerful jaws and swallowed, however, larger prey may be dragged to deeper water before being dismembered and eaten.

The NT-based study was published in Biology Letters on Wednesday.