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Public Radio's Environmental News Magazine (follow us on Google News)

Rodent Roadsigns

Air Date: Week of

Wood mice use sticks, leaves and shells as sign posts so they don’t get lost as they travel through fields. Host Steve Curwood talks with Oxford University zoologist David Macdonald about the rodent road signs.


CURWOOD: Biologists have known for some time that wood mice have excellent navigational abilities. Now, new research suggests one reason why. These little rodents build themselves road markers out of leaves, twigs, and shells.

David MacDonald heads the Wildlife Conservation Research Unit at Oxford University. He first observed this phenomenon in the wild, and he wanted to see if the mice would repeat the behavior in the lab.

MACDONALD: We put the wood mice in a pretty simple arena, provided them with a nest box and some food, and absolutely nothing else at all except some plastic disks, just small bits of plastic. And lo and behold, we found that they went to a lot of trouble to pick up the plastic disks and carry them around, as if they had a deliberate purpose in mind.

CURWOOD: So, what was this purpose?

MACDONALD: Well, it seems that they were doing exactly what you and I would do if we dropped our car keys in the lawn, and then the telephone rings in the house. You’d put a stick in the ground, or some marker in the ground to remind you where the keys fell, so you can continue your search later.

And it looks as if that is precisely what these wood mice are doing. They carry a little disk around with them when they find an interesting place where there are some seeds or whatever to forage for. And then they put the disk down.

And whenever they are disturbed--and you must remember, these are very nervous creatures. They are just always jumping around, being fearful of predators and so forth. But when they have been disturbed, then they find their way straight back to the little road sign, to the marker, just as you would if you had dropped your car keys in the lawn.

CURWOOD: Why do the mice need these signposts?

MACDONALD: Well, most of the time these animals are on farmland, particularly foraging, for example, through cereal fields, cornfields. And so it must be like finding their way through, almost, an ocean of uniform habitat.

And, as I say, they are such nervous little guys that every few moments they are running to the left and to the right from some false alarm, in case a weasel or a hawk is going to strike them. And as they forage, rather interestingly, every few moments you see them stand up on their hind legs and look over their shoulder, as if drawing a bead on where the plastic disk is just so they don’t get disoriented or lost.

CURWOOD: What other animals use these kinds of road markers?

MACDONALD: Well, Steve, as far as we are aware, there’s certainly one other species, namely humans. On the other hand, looking through the literature, there is just no evidence at all of any other mammal species doing this. Now between you and I, I actually expect lots of species do it but nobody’s ever noticed it before. So, so far, the list is only two species long.

Of course, part of the interest is these are very, very familiar animals. Just like the white-footed mouse is familiar in North America, these guys are ten-a-penny in farmland in the U.K. And it’s rather exciting to find such an unexpected and intriguing adaptation in an animal that is very familiar. It shows you, you don’t have to go to a far-off land to watch a charismatic and rare species in order to find out something interesting.

CURWOOD: David MacDonald heads the Wildlife Conservation Research Unit at the University of Oxford in the U.K. Thanks so much for taking this time with us today.

MACDONALD: It’s a pleasure.



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