Zoologger is our weekly column highlighting extraordinary animals ? and occasionally other organisms ? from around the world
Species: Otomys sloggetti
Habitat: The Drakensberg and Maluti mountains in eastern South Africa
All human beings think of themselves as good people ? kind to others and behaving as decently as possible. In reality, we're all dishonest, as psychologists have shown and, under the right circumstances, even seemingly nice people can behave abominably.
Seemingly "nice" animals are just as inconsistent. Did you watch the video of cute sleeping sea otters holding hands so that they don't drift apart? It went viral, and it's authentic. But otters have a dark side: they sexually assault seal pups, wounding and even drowning their victims.
Then there's the African ice rat, another perfect illustration of this dichotomy. In their shared burrows, the rats snuggle up together and are perfectly friendly. But once they are above ground, the gloves come off.
No hibernation
African ice rats are found only in areas at least 2 kilometres above sea level, where the air is chilly and there is often snow on the ground. The creatures seem to have been driven into the mountains fairly recently by the closely related vlei rat.
At first glance the rats don't seem particularly well adapted to their upland habitat. For starters they don't hibernate in winter, unlike many alpine rodents. Worse, their bodily functions work best at ambient temperatures of between 26 and 28 ?C.
"They retain the physiology for lower altitudes," says Neville Pillay of the University of the Witwatersrand in Johannesburg, South Africa.
On the plus side, their small intestines are unusually large, allowing them to absorb more energy from their food and thus keep warm. Their fur is also rather dense, allowing them to retain heat more easily than their lowland relatives.
These adaptations help, but they're not enough. So instead of changing their bodies, the ice rats have changed how they behave. Whereas lowland species live solitary lives, the ice rats work together to dig burrows, where they huddle up together to keep warm.
It sounds harmonious, but it's not. Pillay and his colleagues discovered this by monitoring 10 colonies of wild rats for four years. Each one had up to 17 adults, but in 612 hours of observations, once above ground the rats only interacted 31 times, and 26 of those were aggressive.
Boxing rats
They run up to each other, says Pillay, and start boxing with their front paws. At least in Pillay's experience, the rats never seriously hurt one another. Instead, one would give up and run, and the other would chase it off.
The researchers also ran experiments in which they caged an ice rat ? for its own protection ? before placing it near another rat, either from its own colony or another. The ice rats were almost always aggressive towards each other, regardless of which colony they belonged to. "We wouldn't have predicted that," says Pillay. Once they're above ground, it seems, the ice rats exhibit no allegiance to their colony-mates.
Pillay says food is scarce in the mountains, so the rats must compete furiously to get enough. When he dropped pieces of apple ? which the ice rats love ? the number of fights increased significantly.
"I think this is a compromise," Pillay says. The ice rats are social when they need each other to stay warm, but ferocious loners when looking for food. "It works for them."
Population explosion
It's not clear if ice rat society will change. Heavy snowfalls are the sole brake on their population ? Pillay says they have no natural predators ? but these are becoming rarer. "In the last few decades the ice rats have exploded in numbers, because of climate change," he says. Whereas many alpine species are expected to suffer as the climate warms, the ice rats are thriving.
That could change if lowland predators start moving uphill. Jackal buzzards have started moving in, and on one occasion a buzzard was seen hunting and killing an ice rat. "The ice rats were not prepared for that," Pillay says. Although more social animals like meerkats have alarm calls to warn each other of predators, the ice rats do not.
So while they don't like each other much now, Pillay says that might have to change. If more predators enter their home range, the ice rats could evolve to become more social.
Journal reference: Journal of Zoology, doi.org/mb3
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