Like humans, most animals tend to leave their parents and siblings and strike out on their own. They want to avoid competing with relatives. They want to avoid incest. In certain species, they want to avoid nagging.
But a new paper published in Thursday's Science shows there's at least one species that bucks the trend. Prairie dogs, especially female prairie dogs, stay home. They tend to only leave their native territories when all their relatives are gone.
The paper's author, John Hoogland, didn't notice the pattern for decades. Which is surprising. He knows prairie dogs better than almost anyone.
"Frequently I refer to prairie dogs as my little people," he says. "They have distinct personalities, just the way people do."
Hoogland's office is at the University of Maryland's Center for Environmental Science, but this week he drove for two days to reach his field site in a remote corner New Mexico's Valles Caldera National Preserve.
He'll start this field season just as he has the last thirty — he'll trap each and every prairie dog in his study colony. He'll tag their ears, and just so he can recognize them from far away, he dye their fur with numbers and symbols.
"We've now tracked over these years well over 30,000 prairie dogs, probably closer to 40,000," Hoogland says.
He and his team have studied nearly every aspect of prairie dog life - alarm calls, mating, infanticide. But there was one subject Hoogland didn't much care about.
"I had very little interest in dispersal," he says.
Dispersal - that's when animals leave the place they were born. It's a really important topic for ecologists . Hoogland says a quick Google search will yield thousands of books and hundreds of thousands of papers - all about dispersal.
Perhaps the most important of these papers was written by Robert May and William Hamilton.
"Robert May and William Hamilton are superstars," Hoogland says. "We're talking bout Mantle and Maris for baseball, Michael Jordan and Scotty Pippen for basketball. They had a very testable provacative hypothesis."
The hypothesis was this: If you compete with your family members, the family won't do as well and its genes are less likely to be passed on. To avoid that competition, animals will leave home as soon as they can.
This hypothesis has been proven over and over - in fig wasps and lizards and mice. Hoogland just assumed prairie dogs followed the same pattern. And he never would have taken a closer look if it weren't for the social dynamics of human mating pairs.
Hamilton and May's hypothesis has been proven time and time again.
"It's been shown in something like fig wasps and something called a viviparous lizard and in white footed mice," Hoogland says.
But Hoogland probably never would have looked at prairie dog dispersal if it weren't for a particular case of human social behavior.
"My wife said to me — we talk about prairie dogs all the time — and she said, 'You know what? That dispersal by females isn't happening very often,'" Hoogland says. "And I remember saying to Judy, I said 'There's nothing there. I'm not going to waste my time doing that.' Well, my wife can be very persistant."
And so he crunched the numbers. Hoogland's 30 years of data showed that prairie dogs weren't leaving home.
You often hear about females staying with their family groups, but even in those situations, they'll only stick around if there aren't too many relatives crowding up the place. But here, in the females of three prairie dog species, the opposite was true. The more relatives, the merrier.
Prairie dog males tend to leave their home burrows to find mates. But even they were more likely to stick around.
Why do prairie dogs have such a different dispersal behavior? Researchers aren't entirely sure. But Ana Davidson, a prairie dog researcher and conservationist at Stony Brook University, says the benefits of prairie dog family life outweigh the costs of competition.
"They end up having the same kind of benefits that we do as we do in a sense to having close family," she says.
They can help each other maintain their homes - the burrows they rely on for warmth and refuge from predators. They can also groom each other, removing parasites that carry disease.
"That grooming is part of the connection that the animals create with each other," Davidson says.
It's PDA - prairie dog affection. If a new mother dies, her female relatives will nurse her babies. And if a prairie dog sees predator approaching a close relative, it's more likely to sound the alarm.
All these behaviors help support prairie dogs' communal lifestyle. But Davidson says the creation of large communal colonies is exactly what made prairie dogs a nuisance to humans, and led to their trapping and poisoning. It also facilitates the spread of exotic diseases. Prairie dogs now inhabit only 5% of their historic range.
Davidson hopes that work like Hoogland's will help humans understand prairie dogs and better conserve them.