Crocodiles in Australia Are Shifting Their Behavior Because of Climate Change, and It Might Harm Their Ability to Hunt

Australia’s crocodiles may end up struggling in a warming world. A new study finds the average body temperature of these reptiles has been increasing with climate change, and they are changing their behavior to cope with rising heat.

The animals are resilient, but “they are already close to their physiological thermal limit,” per the paper, published this month in Current Biology. “The impact of future predicted rises in temperature remains unknown.”

Crocodiles are ectothermic—meaning they can’t regulate their own temperatures—so their bodies heat up or cool down depending on their environment. The reptiles travel to more hospitable areas to stay comfortable.

“On hot nights, the water stays warm, but the air cools down. So, crocodiles will move onto the river bank at night to cool off,” write three of the study authors for the Conversation. “During the day, they might dive down really deep where it’s a bit cooler. Or they might lie on the bank in the shade with their mouth gaping wide or sit in a cool, freshwater creek.”

To test whether these strategies help during extreme heat, researchers tagged and tracked 203 crocodiles at the Steve Irwin Wildlife Reserve in northern Queensland. They collected data on crocodile body temperature, daily distance traveled and diving behavior, then compared that to local temperatures.

From 2008 to 2023, average air temperatures increased by between 0.14 and 0.54 degrees Fahrenheit—and the animals’ average body temperature also rose during that period. The crocodiles began to spend more time near their critical thermal limit of 89.6 to 91.4 degrees Fahrenheit, where their performance decreases. The highest recorded body temperatures were associated with El Niño periods.

“During very hot years, we’re finding that their internal body temperatures are starting to reach points where we know their behavior is impacted,” says study lead author Kaitlin Barham, a wildlife ecology researcher at the University of Queensland, to Conor Byrne and Sophie McManus of the Australian Broadcasting Corporation (ABC).

At the hottest temperatures, crocodiles spent less time diving and more time performing cooling behaviors. This aligns with previous research that found overheated crocodiles take shorter dives. “A hotter croc has a higher metabolism,” explains Barham to Live Science’s Richard Pallardy. “Higher metabolism means burning oxygen more rapidly. Lab research found that they just couldn’t hold their breath for as long. It would take them a bit longer to recover at the surface.”

Since crocodiles are ambush hunters that rely on staying submerged for the element of surprise, the scientists are worried that shorter dive times might impact their ability to hunt, according to a statement. It could even affect how well crocodiles can escape from predators or travel, researchers tell the ABC.

“Every minute that they’re up on the bank trying to bring their body temperature down is a minute that they’re not spending traveling, reproducing or looking for food,” Barham adds to Live Science. “That could result in future indirect effects on their health.”

Climate change isn’t just affecting the crocodiles. It’s also making things harder for tour guides in the region. “Warmer water makes my job very difficult, because the crocodiles spend a lot of time on the bottom where it’s cooler, and they’re very hard to find in the summer months,” wildlife guide David White, who was not involved with the study, says to the ABC.

The current research focused on the northern part of the crocodiles’ range, and the scientists would like to see more analysis on the southern parts. “It would be really interesting to see how crocs that live at the southern part of their range in Australia, where they’re a bit cooler, cope with similar heat waves,” says Barham to Imma Perfetto at Cosmos magazine.

So far, scientists haven’t uncovered any evidence that the northern crocodiles are moving south to seek cooler temperatures. “Our research suggests they have the capacity to buffer themselves against the worst of the heat our current climate throws at them, without leaving their local river system,” the team writes in the Conversation. But the projected future warming “suggests crocodiles might struggle.”

White has faith in the animals’ resilience. “They’ve gotten through all those terrible climate changes that the dinosaurs couldn’t cope with and the meteorite strikes,” he says to the ABC. “I think they will adapt and get through it.”

Sara Hashemi | READ MORE

Sara Hashemi is a science writer and fact-checker currently based in New York City. Her work has appeared in Sierra, The Body, Maisonneuve magazine and more.