Mice make signposts out of leaves and twigs so that they do not get lost in fields, new research shows.

This behaviour surprised Pavel Stopka and David Macdonald, who were studying wood mice captured near their laboratory at the University of Oxford, UK. Primates and some birds are known to use sticks and stones to place markers within their territory. “But no-one would expect mice to be so clever,” says Stopka.

The excellent navigational abilities of the wood mouse (Apodemus sylvaticus) have been extensively studied, but their way-marking trick had remained undiscovered until now. The latest work suggests the mice move objects to mark sites that interest them, perhaps because they are abundant in food or a quick route back to their burrow.

As the mice explore the area around the object, explains Stopka, they regularly rear up on their tiny back legs to look for their signpost, and dart back towards it before moving away in a different direction.


Statistical link

The researchers analysed this behaviour in a laboratory by keeping eight wood mice, four male and four female, in a two-by-two metre enclosure. Ten white plastic discs, each five centimetres across, were placed in the centre of the arena.

The mice appeared to play with the discs, moving them around. But a statistical analysis of their movements, based on continuous videos of their behaviour, revealed a strong link between their movements and the position of the discs. They seemed to be using the discs as markers to orient themselves in the otherwise featureless box.

Marc Jamon from the Institute of Physiological and Cognitive Neurosciences in Marseille, France, has also studied the trail-following ability of wood mice and says: “The observation is very interesting and deserves to be tested further.”

But he also suggests an alternative explanation: “Possibly the discs are the only objects to explore and are competitively moved by different animals.”

Very bland

The wood mice might need to use signposts because the fields where they live are very bland – one patch of ploughed field looks much like another, says Stopka. And while some other mice use scent markers, wood mice are wholly visual, says Stopka: “They have big eyes.”

Piles of leaves, twigs and even shells have been associated with wood mice before, but it was assumed they were used to hide nest-holes. The first hint of their function as signposts came when one group of mice escaped from their laboratory box.

Stopka says: “One dug a hole through the side, and the last one out marked it with a leaf. We repaired the hole – but when we put them back in they still ran towards the leaf.”

Journal reference:BMC Ecology(2003 3:3)