You’ve heard of the canary in the coal mine — the metaphorical warning that things are about to take a turn for the worse — but have you heard about the squirrel in the burrow? No? Well, today you will.
Come with me to South Africa, where University of Manitoba researcher Jane Waterman has been studying Cape ground squirrels for more than 20 years.
Cape ground squirrels might remind you of prairie dogs. They live communally, in burrows, and have some fascinating social practices. As with a lot of squirrels, related females live together in groups. But males also stay a part of the colony for longer than in other species.
“They overwhelmingly delay leaving home, but they don’t mate with the family group,” Waterman said. “They stay home and care for the kids. It’s kind of weird.”
And when the males do disperse and join all-male groups, they get along. They’re not aggressive with one another.
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Waterman is primarily interested in squirrel behavior: What squirrels do and why they do it. As part of her research, she compiles data on the squirrels’ morphology — size, weight, etc. — and on the environment in which they live. This interested a postdoctoral researcher named Miya Warrington, who came aboard two years ago.
“Miya is amazing with data,” Waterman said. “She asked, ‘Have you ever looked at temperature on the site and body size?’”
They hadn’t, so Warrington took the numbers and crunched them. She found that over the last two decades, the maximum temperature on the South African study site had risen by more than 2 degrees Celsius. Over that time, the spine length of the squirrels had gotten smaller and the relative size of their feet had gotten bigger.
“This is exactly what you would expect if the animals were trying to dissipate heat,” Waterman said.
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Biologists have long known that a smaller body and larger feet help animals endure higher temperatures, the sort of temperatures that are rising all over the planet.
Meanwhile, more than 9,000 miles away lives another species of squirrel Waterman studies: Richardson’s ground squirrel. These squirrels, found in western Canada and the northern United States, aren’t as social as their South African cousins, and they hibernate.
“Hibernating species are really cool,” Waterman said. “They have their lives really timed to miss the worst times of the year. I wish I was a hibernating species in some ways. You miss winter and just wake up when it's nice.”
But the Richardson’s ground squirrels may also be revealing how climate change could affect animal biology.
Male Richardson’s ground squirrels emerge from their slumber before the females, driven by an as-yet-unknown internal clock. In their time above ground, males fight with each other to establish territories. Two or three weeks later, the females emerge, driven by an increase in temperature. After a few days, females are ready to mate and the copulation competition begins.
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But something odd happened in 2012. That winter, temperatures rose quickly, sending females out of their burrows earlier than normal. The males hadn’t been out on their own very long and when Waterman tested their sperm — she really does look at everything — she found … nothing.
“They were shooting blanks,” she said.
The male squirrels appeared normal — their testes were nice and big — but their internal plumbing wasn’t online yet. The male squirrels hadn’t had the alone time they needed for everything to get percolating.
Eventually, the sexes synced up and plenty of babies were produced, but the implications were eye-opening.
Said Waterman: “The females were able to have normal-size litters — they breed with more than a single male — but you have to think about it: If this were to happen on a regular basis, which potentially these sort of temperature extremes climate change could make more common, you’re reducing genetic heterogeneity. There’s not as much variation because half the males are not able to breed successfully.”
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Changes in climate could affect things back in Africa, too — and not just the size of Cape ground squirrel feet.
“These squirrels are ecosystem engineers,” Waterman said. “Burrowing mammals, especially social burrowing mammals, have a really big impact on grassland communities.”
Ground squirrel burrows affect other small mammals in the ecosystem. They affect the plants that grow there, including some plants eaten by antelope.
“When you’re affecting [squirrels’] morphology and their physiology, you could also be affecting their sociology,” Waterman said.
The research by Waterman and Warrington appeared in the Journal of Mammalogy.
The University of Manitoba studies reflect two sides of the climate change coin: The population of Cape ground squirrels was affected gradually, with subsequent generations of animals having bigger feet and shorter spines. The Richardson’s ground squirrels experienced a quick shock: a temperature spike that had the potential to throw reproduction out of whack.
The squirrels may be trying to tell us something. Are we listening?
Tomorrow: Squirrel Week continues.
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