Mystery mouse at Mincinglake

This construction was an autumn-winter DIY project. 

House for a mouse, interior

It's a 'mouse-arium', now completed and stood where the TV used to be: I'm looking after three long term, quite possibly permanent, house guests, or mouse guests. Devon Mammal Group has acquired a number of harvest mice indirectly from the captive breeding scheme at Chester Zoo. These rapidly did their thing, and before anyone knew it there's now an impromptu captive Devon population as well, some needing homes.

These can't just be released into the wild. There are several major questions to resolve first: what is the current status of harvest mice in Devon, and are there many suitable sites out there, with decent potential habitat? Are harvest mice already here? And if not, why not? 

Nobody knows, and there's little understood about harvest mouse distribution in Devon, with very few site records held at DBRC. The national mammal atlas 1993 shows a scattering of records across south Devon, with blank white spaces in the mid and northern areas of the county. This could well be a lack of looking than lack of harvest mice.

This is why Devon Mammal Group has set up a new county wide survey project to discover more. A training day at Stover Country Park in November, with excellent tutoring from The Mammal Society's Derek Crawley, showed us where and how to look; in a couple of hours our novice group found some 18 nests across two areas of the Country Park. The first was found within 5 minutes, a text book example grass-woven pom-pom attached half way up a reed stem amongst dense cover. This attachment to surrounding vegetation above ground level is a diagnostic feature.

Mouse house, exterior

Armed with such new knowledge, trained surveyors will explore sites around their local patches, for harvest mouse field signs of old summer nests. Harvest mice, we learned, need thickly-packed sward. They are tiny, about pygmy shrew size, about 5cm, with another 5cm of tail, and weigh around 7-8g (or as much as a 50p coin), which helps, as they like to climb. For this they have a tiny reach, hence grass and other upright stems need to be close together, and interlinked. Also harvest mice do not collect or transport nesting material to a nest site location, but must use whatever is to hand, or rather paw. 

This means the best places to start looking are among banks of thickly growing coarse grasses like Cock's-foot, or reeds, which haven't been cut or grazed for over a year or more, forming an impenetrable grassy forest. In high summer, nests should be impossible to find in this matrix of stems; instead the ideal time to survey is autumn-early winter, after vegetation dies down and before the attrition of winter weather destroys the old nest structures.

So .... a mouse mission, off on the trusty bicycle to check out some of Exeter's Valley Parks and other wilder, grassier, green spaces.

Mincinglake mouse habitat

Ludwell, Duryard and Barley Valley were now grazed down to short grass, and unsuitable. DWT's reserve at the Old Sludge Beds, where harvest mouse nests have been recorded in the past during reed-cutting management works, was not accessible off the boardwalk path. At Mincinglake, with unmown, extensive stands of Cock's-foot and other tall grasses, it was a different matter. 

Crouched peering face first while teasing through the dense sward might have looked slightly odd to any dog-walking onlookers. Two hours of this did not meet with any particular success, though there were plenty of vole signs in the form of runs and piles of nibblings under the matted canopy layer of collapsed old stems, and the habitat still appeared promising.

Teamwork is probably the answer: a few days later a group 30 strong from University of Exeter spent a similar amount of time here, discovering one genuine wild Exeter harvest mouse nest. It's official and wildlife-newsworthy - so little is known, but harvest mice are at Mincinglake, a valuable record for the city and the county. It fills in a blob on Devon Mammal Group's map,

though it took 60 person hours to find field signs of them.

If old nests are hard to find, practical chances of seeing live animals in the wild must be zero. Here are some pictures from the mousearium instead. It's fascinating viewing, watching them investigate new objects, pathways and food items. They are welcome to stay as long as they need.

Better than TV: watching the mousearium residents

UPDATE end of December 2016
Success! Wild harvest mouse nest found at Mincinglake over the Christmas break. Merry Xmouse!

Living on the sedge: Harvest mouse nest in clump of Pendulous sedge

 
For more harvest mouse info, visit this great harvest mouse webpage.

For anyone interested in surveying for harvest mice around Devon, further Devon Mammal Group workshops are to be held through 2017.