WOOD MICE make signposts out of leaves and twigs to help them find their way as they scamper around featureless fields.
鈥淣o one would expect that mice would be so clever,鈥� says Pavel Stopka, who made the discovery. Primates and birds use sticks and stones as markers in their territory, and the amazing navigational abilities of the wood mouse (Apodemus sylvaticus) have been studied extensively. But till now, no one had spotted the rodents鈥� signposting skills.
The mice appear to move objects to mark sites that interest them, such as places where there is plenty of food or a quick route back to their burrow. As they explore the area around the signpost, Stopka noted, they regularly rear up on their hind legs to look for it, then dart back towards it before moving away in a different direction.
Advertisement
Stopka, now at Charles University in Prague, and his colleague David Macdonald at the University of Oxford videoed four male and four female wood mice kept in an enclosure 2 metres square, in the centre of which the researchers placed 10 white plastic discs, each 5 centimetres across.
The mice repeatedly picked up the discs and relocated them. A statistical analysis of their behaviour revealed a strong link between their movements and the position of the plastic discs. They seemed to be using them as markers to orient themselves in the otherwise featureless box (BMC Ecology, 2003, 3:3).
But Marc Jamon from the Institute of Physiological and Cognitive Neurosciences in Marseille, France, who has studied the trail-following ability of wood mice, has another interpretation. Instead of moving them to form signposts, the discs could simply be the only objects in the enclosure worth exploring. The animals may move them as a way to compete with their rivals. But he agrees that the study raises a fascinating possibility that should be investigated further.
鈥淲e know that wood mice are wholly visual 鈥� they have big eyes,鈥� says Stopka. House mice, by contrast, rely on scent markers. In the woods and fields inhabited by wood mice, scent markers would alert predators to their presence, or lead to conflict between animals whose territories overlapped.