JOHN HOOGLAND

Prairie dogs are cute. They scamper in and out of holes in the ground and stand on two legs staring towards the sun. But according to a new study published in Proceedings of the Royal Society B., while they do this they might be thinking about attacking and killing ground squirrels.

According to the study, it's exceedingly rare for an herbivore to regularly kill another herbivore, and it really caught John Hoogland, who works at the University of Maryland Center of Environmental Sciences and co-authored the study, by surprise.

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“In my 43 years of research, this is perhaps the most provocative, puzzling, and far-reaching discovery I’ve ever made,” he told National Geographic. “The results are just staggering.”

What the results suggest is also surprising: that the females that kill more ground squirrels raise more offspring during their lifetimes than the ones that don't kill.

Hoogland and study co-author Brown believe that their findings suggest that white-tailed prairie dogs—native to Colorado, Wyoming, Utah, and Montana—and ground squirrels compete for food resources, feasting on at least six of the same plant species, and this is why they engage in bloody battles.

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In order to reach these conclusions, Hoogland and his students studied prairie dog behavior in the scrublands of western Colorado’s Arapaho National Wildlife Refuge for six years. During this time they witnessed 101 lethal attacks, mostly from female prairie dogs, and they inferred 62 more from dead squirrel carcasses. They determined that "A propensity for killing ground squirrels turned out to be the only factor (among such possibilities as body mass, age and number of neighbors) that predicted a tendency toward lifetime success in raising lots of young. That factor, which biologists describe as fitness, is a big deal in analyzing how populations change and species evolve."

However, the authors caution from jumping to the conclusion that serial-killing prairie dogs necessarily have an evolutionary advantage. They say that more research will be required to rule out the possibility that the killer prairie dogs happen to live in areas with more vegetation, thus attracting more ground squirrels and triggering more conflicts between the two competing species.