From terrorist attacks to muggings, people are clearly among the most violent of species, but new research suggests that unprovoked killing not associated with hunting could be far more common in the animal kingdom than previously thought.
It appears that killing to reduce competition between species happens frequently, even when the killer is an herbivore that could care less about eating its victim.
A new paper published in the journal Proceedings of the Royal Society B documents how herbivorous white-tailed prairie dogs regularly kill Wyoming ground squirrels, leaving behind bloody bodies that the killers have no desire to eat.
Photos: Prairie Dogs Revealed as Serial Killers
"I describe the behavior in eight words: catch them, shake them, kill them, leave them," lead author John Hoogland of the University of Maryland Center for Environmental Science's Appalachian Laboratory told Discovery News.
Hoogland and co-author Charles Brown had no idea what they were in for when they took on a project to study the basic behavior of veggie-loving white-tailed prairie dogs. Sitting in an observation tower surrounded by the animals, Hoogland started to notice the unprovoked killings.
The researchers identified 47 prairie dogs that made kills: 36 were female, 11 were male. Thirty percent of all females killed at least once in their lives. Nineteen females were serial killers in the same or consecutive years.
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The scientists investigated the phenomenon further and found that the female serial killers had significantly higher annual and lifetime fitness than the other females did. The scientists believe that the killings reduce competition for space and food with the ground squirrels.
They also suspect that natural selection favors females that kill, but this selection process does not necessarily make them any more aggressive with their own kind.
"It's not that certain nasty females only do this," Hoogland said. "In fact, the female serial killers will often dispatch their victims and then go on to graze peacefully or play with their babies, as though nothing had just happened."
He added, "I don't even think the prairie dogs are physically well equipped to eat ground squirrels."