Many species are suffering at the hands of a warmer world, but one California inhabitant seems to be enjoying hotter temperatures: the Pacific rattlesnake. Their populations across the south-west are thriving, according to a study by researchers at Cal Poly San Luis Obispo and the University of Michigan.
The study found that when given the choice, rattlesnakes – which cannot control their own temperature and rely on the environment for warmth – actually prefer to live in places where the climate averages more than 80F, suggesting they’re likely to do well as the planet gets hotter.
“The moral of the story is that as temperatures rise, it approaches the snakes’ optimal temperature,” says Hayley Crowell, lead author of the study, which was released last year. “That’s a favorable change for these snakes.”
Crowell and her colleagues didn’t set out to investigate climate change – they wanted to know more about physiology and thermal ecology of rattlesnakes: how they warm up and cool down, comparing seven species of rattlesnakes living in coastal areas and central California. They wondered how the same snake can live in cool foggy areas and high arid deserts, considering they can’t control their own temperature.
The researchers implanted small temperature loggers – about the size and shape of a watch battery – inside the snakes to record how warm they were. They found the average internal temperature of coastal rattlesnakes is usually 70F, while inland rattlers have an average of 74F.
They also brought snakes into the lab and set them in a box that had different temperature areas, letting the snakes pick where they wanted to sit. Given the choice, the snakes preferred their body temperature at a balmy 86 to 89F – much higher than their temperature in nature. “All the snakes were choosing higher temps,” says Crowell, “warmer than where they were living.”
Being warm brings with it certain benefits: the snakes can spend more time out of hibernation, more time growing, and more time reproducing. They typically hibernate from September to May, but this could shorten in the future. Even on a given day, the snakes could have more active hours as the temperatures rise.
The snakes digest very slowly, and need to eat only about 500 to 600 calories a year – the equivalent of a single ground squirrel. (Humans, on the other hand, need more than 1,300 times more calories to survive.)
While warmer temperatures may make it easier on their bodies, the changing climate can threaten snakes in other ways, Crowell says. More heat can mean more fires, less available water during mega-droughts, and it might not be great for ground squirrels, which happens to be the food rattlesnakes are specialized to eat. There’s also a tradeoff of staying in the sun to bask for too long: a hawk might see the snake and go in for a meal.
Rising temperatures could mean more snakes in the future, but not an overwhelming number: “I don’t think there will be thousands more snakes,” she says. “You might see more, if their food allows it.”
Each year, about 300 Californians a year are bitten by rattlesnakes, according to the California Poison Control System, though the risk of death from a rattlesnake is lower than the risk from a dog attack or a lighting strike.
Overall, rattlesnakes are ideal model organisms for examining the physiological effects of climate on cold-blooded animals, the researchers say – because their life-history traits, simple behaviors, and metabolism are well studied.
Crowell is now studying how snakes deal with different environments and balance their water uptake. She also wants to know how their colors – which differ widely between different areas – play a role in their heating and cooling systems.
Rattlesnakes are some of the most hearty creatures around, she says: “They have a pretty wide thermal tolerance, a super low metabolism, only eat a half-dozen meals per year,” she says. “So they are pretty content just hanging out, as long as it’s not too hot or too cold.”