Cape ground squirrels might remind you of prairie dogs. They live in communities, in burrows, and have fascinating social practices. As with many squirrels, related females live in groups. But the males are also part of the colony longer than in other species.
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“They massively delay leaving home, but they don’t mate with the family group,” Waterman said. “They stay at home and take care of the children. It’s a little strange.”
And when males disperse and join all-male groups, they get along. They are not aggressive with each other.
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 morphology of squirrels — height, weight, etc. — and the environment in which they live. This interested a postdoctoral researcher named Miya Warringtonwhich happened two years ago.
“Miya is amazing with data,” Waterman said. “She asked, ‘Have you ever looked at the temperature on the site and the body size?'”
They hadn’t, so Warrington took the numbers and crunched them. She found that over the past two decades, the maximum temperature at the South African study site had risen by more than 2 degrees Celsius. During this period, the length of the squirrels’ spines had become smaller and the relative size of their feet had become larger.
“It’s exactly what you would expect if animals were trying to dissipate heat,” Waterman said.
Biologists have long known that smaller bodies and bigger feet help animals withstand higher temperatures, the kind of temperatures that are rising all over the planet.
Meanwhile, more than 9,000 miles away lives another species of squirrel studied by Waterman: Richardson’s ground squirrel. These squirrels, found in western Canada and the northern United States, are not as social as their South African cousins and they hibernate.
“Species that hibernate 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 you wake up just when the weather is nice.
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But Richardson’s ground squirrels could also reveal how climate change could affect animal biology.
Male Richardson’s ground squirrels emerge from sleep before females, driven by an as-yet-unknown internal clock. In their time above ground, the males fight against each other to establish territories. Two or three weeks later, the females emerge, pushed by an increase in temperature. After a few days the females are ready to mate and the copulation competition begins.
But something strange happened in 2012. That winter, temperatures rose rapidly, causing females to emerge from their burrows earlier than normal. The males hadn’t dated alone for very long and when Waterman tested their semen – she really looks at everything – she found…nothing.
“They were shooting blanks,” she said.
The male squirrels appeared normal – their testicles were nice and big – but their internal plumbing was not yet online. The male squirrels hadn’t had the alone time they needed for everything to seep through.
Eventually the sexes synced up and many babies were produced, but the implications were eye-opening.
Said Waterman: “The females were able to have normal sized litters – they breed with more than just one male – but you have to think about it: if that were to happen regularly, what potentially this kind of extreme temperature climate change could make more common, you reduce genetic heterogeneity. There is not as much variation as half of the males are not able to reproduce successfully.
Climate change could also affect things in Africa – and not just the leg size of Cape ground squirrels.
“These squirrels are ecosystem engineers,” Waterman said. “Burrowing mammals, especially social burrowing mammals, have a very large 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 antelopes.
“When you assign [squirrels’] morphology and their physiology, you might also affect their sociology,” Waterman said.
Waterman and Warrington’s research appeared in the Journal of Mammalogy.
The University of Manitoba studies reflect both sides of the climate change coin: the Cape ground squirrel population was affected gradually, with subsequent generations of animals having larger feet and shorter spines. Richardson’s ground squirrels suffered a rapid shock: a temperature spike that had the potential to disrupt reproduction.
Squirrels may be trying to tell us something. Are we listening?
Tomorrow: Squirrel week continues.
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