Between 2008 and 2023, researchers conducted a comprehensive study on 203 estuarine crocodiles at the Steve Irwin Wildlife Reserve in Queensland. This extensive research aimed to understand how global warming is affecting these stealth predators, which are increasingly struggling due to rising temperatures in Australia. The findings, published in the journal Current Biology on February 12, reveal significant changes in the crocodiles' behavior as they adapt to the warming environment.
The study recorded nearly 6.5 million temperature readings from the monitored crocodiles. A key finding was that body temperatures of 89.6 degrees Fahrenheit (32 degrees Celsius) or higher led to reduced swimming and diving performance, crucial activities for these creatures that rely on stealth and ambush tactics to hunt their prey. The researchers observed that the highest body temperatures increased by 0.99 F (0.55 C) over the study period, reflecting a small yet significant rise in average body temperatures.
During the study, 135 out of the 203 crocodiles showed body temperatures exceeding 89.6 F at least once. One particular crocodile exhibited such high temperatures for over a month in 2021. Kaitlin Barham, a key researcher in the study, explained that "a hotter croc has a higher metabolism," which can adversely affect their overall health and ability to thrive in their natural habitat.
Estuarine crocodiles must regulate their body temperature to avoid reaching their critical thermal limit. When their body temperature rises, they seek shade, retreat to cool streams and pools, or bask on the shore at night. This need for cooling down interrupts their usual activities. Barham stated, "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."
The study noted that the highest body temperatures were linked to El Niño periods, during which unusually warm Pacific currents led to hot, dry spells on land. These conditions exacerbate the challenges faced by crocodiles, as they spend more days at their thermal limit.
Researchers employed meticulous methods to track temperature changes in these reptiles over time. If a crocodile was not detected for a period ranging from 30 minutes to 24 hours and later reappeared with altered body temperatures, scientists assumed it had changed its behavior to regulate its temperature. Barham described a typical observation: "The croc would disappear for a few hours, and then come back 1 or 2 degrees [C, or 1.8 to 3.6 F] cooler."
The impact of global warming on estuarine crocodiles is becoming increasingly evident. As these reptiles spend more time cooling down, their opportunities for hunting and other vital activities diminish, potentially affecting their survival and reproduction rates. This situation underscores the broader implications of climate change on wildlife and ecosystems worldwide.
