Avoiding feces may be ‘luxury’ wild mice can’t afford

Mice in the wild have no problem dining where someone else has pooped. Animals with higher standards of hygiene, reported in earlier studies, may not face the same dangers as small, hungry creatures scurrying around the woods.

Feeding among feces of your own species raises the risk of catching nasty intestinal parasites, explains behavioral ecologist Patrick T. Walsh of University of Edinburgh. So far most tests of fecal avoidance have focused on hoofed animals. Horses, cows, sheep, reindeer and even wild antelopes tend not to graze in heavily poop-dotted areas.

White-footed and deer mice, however, show no such daintiness of manners in a test in the woods, Walsh and his colleagues report in the September Animal Behaviour. Wild mice may have more immediate problems, like starvation or predators that domesticated–or just plain bigger–animals don’t. For the wild mice, Walsh says, fecal avoidance may be “a luxury.”

Learning whether and when animals avoid poop helps clarify how parasites spread, an issue important for the health of both wildlife and people. So far no one has tested fecal avoidance for mice feeding in the lab, but research has shown that female lab mice tend to avoid the urine of parasite-infected males.

To see whether mice in the wild dodge parasite risks, Amy Pedersen, a coauthor of the study also at Edinburgh, designed an experiment with a long plastic box divided into zones, some of which had mouse droppings in them. In the experiment, researchers tested more than 130 wild Peromyscus mice, of either the leucopus or maniculatus species, held captive for less than a day in the mountains of Virginia.

Mouse droppings by themselves, whether infected or free of parasites, proved more attractive than they were repellant. A mouse left to scurry at will was more likely to hang out in a zone with droppings than would be expected by chance. In a risky world, the researchers imagine, poop might suggest a safe spot where another mouse had survived at least long enough to defecate.

When researchers put seeds in the box, the mice ate just as many from a pile beside droppings as from a poop-free zone. For mice used to life in the woods, Walsh says, “any chance to eat something is taken.”

“Based on my own observations, I totally believe the Walsh results that mice don’t avoid areas that are contaminated with feces,” says disease ecologist Kathleen LoGiudice of Union College in Schenectady, N.Y. She’s studied the willingness of white-footed mice to dig out seeds from raccoon droppings despite the risk of catching a fatal parasitic roundworm.