Monday 20 October 2014

Desperately seeking Micro-mouse

Guest author: Laurie Jackson

In autumn 2012, I was walking through one of Gatwick's meadows with Rachel when my eye was drawn to something on the ground. A tiny woven nest tucked amongst recently-mown grass...

I recognised it straight away as a Harvest Mouse nest. Known rather aptly as Micromys minutus, its Latin name gives a clue to this mammal's diminutive size. Averaging 6-8g, an adult weighs about the same as one long-tailed tit (or 100 of Gatwick's Honey Bees).
   Harvest Mice inhabit a range of habitats including rough grassland, wetlands, scrub and arable margins. They spend most of their time above ground-level climbing through vegetation. It is here they build their characteristic spherical nests - using rigid stems to support or suspend them from. Stripped grass is neatly woven around these supports, forming a structure to rival any of Brunel's creations. Engineer, climber, is there no end to this tiny rodent's skills? I believe the harvest mouse may also be an illusionist…

A Gatwick Harvest Mouse - found with Surrey and Sussex Mammal Groups in 2013

Over the past year I have become more and more interested in this species. After a bit of reading, I soon found I knew more about harvest mice in Japan than I did about those in my local patch! I felt uneasy when I saw the current distribution map for Sussex; with less than 150 records, there is a lot of white space on our county map. Despite this evidence to the contrary, I believe that beneath our feet a miniature army is gathering.

I am keen to find out more about Sussex's Harvest Mice and uncover new populations. To kick this off, I recently led a field trip at Gatwick to show people how to search for signs. Autumn is the perfect time for Harvest Mouse surveys, as the vegetation dies down, making it easier to find their nests. Populations of this species fluctuate annually and I have a feeling this year will have produced a bumper crop. More mice mean more nests, and in little over an hour of searching we had found 12 nests in Gatwick's North West Zone. That's a 10% increase in records… or it would have been if our search area wasn't in the vice county of Surrey!
 Our average nest diameter was 6.25cm, at an average of 40.5cm above ground level.

The star find of the day was a disused breeding nest found by our intrepid University of Brighton students. The nest still contained green vegetation, indicating it was a new-build and that breeding had probably continued into October.

Ecology student Scott has got the hang of it...

Having read this far, your mind is surely filled with just one thought - I want to look for Harvest Mice too! I guarantee that the excitement and anticipation of searching for their nests will liven up any autumnal walk. Throw in the element of danger for those fearless surveyors rooting around in bramble patches (and perhaps a pub stop along the way), what isn't there to love about a harvest mouse survey?

For more information and to get involved with the hunt, please contact me (Laurie Jackson) through the Sussex Mammal Group Website

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