The finding is significant as this is the first time such sophisticated behaviour has been identified in any mammal except humans. According to the authors, "This is precisely how a human might tackle the problem of searching efficiently in a homogeneous environment - for example by placing a cane in the ground as a reference point from which to search for a set of keys dropped on a lawn."
Quick, effective navigation is vital for the wood mouse. Home-ranges are vast in comparison to the mammal's size and consist of uniform areas, like ploughed fields, without obvious landmarks. These environments are not the same all year round, and harvest time drastically changes the availability of any 'fixed' landmarks, food supplies and hiding places.
During field observations, Pavel Stopka and David Macdonald from the Department of Zoology at the University of Oxford noticed that wood mice move piles of seed shells, leaves and other small objects as they explore. They observed that the mice are most active around these piles and frequently return to them.
Stopka and Macdonald brought wild mice into a controlled environment to see if they were using these items as 'portable signposts'. Ten groups of 4 male and 4 female mice were put into special arenas with a nest box, food supply and bedding, and given 10, 5cm diameter white discs.
Mice were videoed constantly for 15 days, and their movements analysed. Activity around the nest box tended to consist only of short, local meanderings not based upon the location of the nest. Movement around the discs, however, involved longer journeys associated with exploratory behaviour. This behaviour was observed in both males and females.
When a mouse found an area it was interested in, it would collect a white disc and move it there. The mouse would then continue to explore, its movements focused on the disc's location. Stopka and Macdonald observed that the mice would continually return to or 'look for' the disc - apparently using it to orient themselves. Once the mouse had finished searching a particular area and identified a new point of interest, it would pick up the disc, move it to the new area and repeat the exploration, again using the disc for orientation.
The discs also served as 'book marks' for when activity was interrupted. If a predator were detected, the mice would retreat to shelter. Once the threat was over, the mice returned to the disc.
Stopka and Macdonald hypothesise that these signposts are more effective for wood mice than scent marks: they can be moved at any time and are not detectable by predators.
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