Saltwater crocodiles in Australia nearly survived extinction by adopting a taste for terrestrial prey, a new study shows.
Charles Darwin University researchers studied how the large carnivores changed their food preferences in the late 20th century, at a time when their populations were declining dramatically.
The results, Published in biology letters from the Royal Society, suggest this may be what saved them, making them a “success story” compared to other large, endangered carnivores around the world.
Australia’s entire saltwater crocodile population was nearly wiped out in the 1900s, and by 1970 there were only a few thousand left in the country, the study found.
As global trade laws were introduced to conserve the species — and reduced the amount hunted for its skin — the population began a steady recovery. Scientists found that in some areas, like Australia’s Northern Territory, population numbers began to skyrocket.
However, population recovery has been slower in other areas such as Queensland and areas in Western Australia. Researchers collected crocodile bone samples from the northwestern areas of the Northern Territories between the East Alligator River and Darwin Harbor to find out how the population grew so rapidly.
The bones were collected from crocodiles that lived between 1968 – a time when there were only a few thousand crocodiles left – and 1986 – a time when the population rose to over 100,000.
The researchers found evidence that points to a “major shift” in the prey hunted by the crocodiles over the years.
Crocodiles had stopped preying on marine animals like fish, frogs and crustaceans during this time, turning their attention to hunting land-roaming animals like Australia’s invasive species of wild boar. The invasive wild boar is widespread in the Northern Territories. The slower recovery of crocodiles in Western Australia could be attributed to fewer land mammals like this one in the region.
Mariana Campbell, research associate and laboratory director at Charles Darwin University and author of the study, tells news week that if the crocodiles had not adapted in this way, the species “probably would not have shown such a strong population recovery”.
“She [would have] red-dispersed into the freshwater flood plains,” said Campbell. “Research shows that crocodile recovery has a significant impact on freshwater and terrestrial food webs in these areas. Crocodiles are opportunistic feeders and will often take whatever prey is available to them. So the change in diet is probably due to what prey is immediately available to them.”
The study states that further research is needed to “better understand the relationship between prey availability, bioenergetics and growth in crocodile populations”.
Campbell tells news week that the next steps for the researchers are to assess the ecological impact of the ever-growing crocodile population.