The Wood Mouse - very common but rarely seen or appreciated!

Spot the Wood Mouse...

This article contains links - these are not affiliate links and we are not sponsored by anyone!

After attending a small mammal trapping event recently I've grown to appreciate just how common the wood mouse (Apodemus sylvaticus) is. It is literally everywhere. And apparently, it loves hanging round people because we are messy so there is plenty of opportunity for food and shelter. So what's so special about the Wood Mouse?

Wood Mice live in large social (family) groups in a  burrow, and have a territory they defend from other social groups. They are highly adaptable to different living situations but as they preferably eat grains and seeds, they are mostly prevalent in agricultural settings, and are considered a serious agricultural pest species. Normal life span of a wild mouse is about 9 months, and they are mature at 21 days. This means that a female mouse can breed several times in the year and can produce up to 30 young in her lifetime. That is why some years mice can reach plague proportions in farm settings, as was the case in Australia in 1993. It is not easy to control mice numbers with trapping or poison, and with their rapid rate of reproduction they are almost unbeatable.

Mice are naturally heavily predated upon by cats, birds of prey, foxes and various mustelids. This will in a naturally balanced setting control the population but in an artificial environment like an intensively farmed area, predation cannot control the numbers of mice.

A lot of people are afraid of mice, perhaps because in our distant past they could be a cause of famine due to their effect on agriculture and also carriers of disease. In terms of health, humans can contract leptospirosis from contact with mouse urine. Leptospirosis is a bacterial infection and in 90% of cases, it only causes mild flu-like symptoms, such as a headache, chills and muscle pain but in some cases it can cause more serious complication called Weil's Disease. Mice are also a carrier of Lyme's Disease that can transfer to people through tick bites, although in many places deer is the main source of ticks infected with Lyme's. Mice are also reportedly responsible for a lot of fires, as they have a penchant for chewing electrical wires and cables! In a modern domestic setting however you are most likely to get in contact with a mouse through 'presents' your pet cat may bring you occasionally, so you shouldn't need to worry about mice.

Despite being called House Mouse (Mus domesticus) the mice you would usually find in and around your house is not House Mouse but rather Wood Mouse! House Mice are considered fairly rare nowadays, possibly due to competition with the more aggressive, highly adaptable Wood Mouse. So how do you tell what mouse your cat has graced you with?... Wood Mice are brown on the top and have white-grey fur on the belly. A House Mouse will have a dark greyish fur all over. And how can you easily tell them apart from voles? As opposed to voles, mice have a very long tail, easily the length of their body. Voles have very small ears which cannot really be seen through their fur, but a mouse's ears are large and protrude from their head. The mouse's bouncy gait also separates them from the more bumbling run of the voles.

This video from our training day shows the characteristic face and ears of the Wood Mouse, and it's unmistakable pale tummy that separates it from the House Mouse!

For scientific study, Wood Mice are trapped the same as most other small mammals, using a humane trap. The one used in our course was a Longworth trap with a shrew hole. It is a legal requirement to have a shrew hole on your trap unless you intend to capture shrews, in which case you need a license to do so in both England/Wales and Scotland. The shrew hole allows all species of shrews to escape as they cannot tolerate capture for more than 4 hours due to their high metabolic rate.

The traps are usually baited with peanut butter and porridge oats. The peanut butter has a strong smell so attracts the mice in from as far away as 25 meters. The porridge oats gives them some food and there should also be some straw/hay in the trap chamber to keep them warm during the night. It is not wise to use shredded paper as insulating material as this gets damp very quickly and then won't provide the warmth and it also absorbs urine and becomes soggy.

Trail cameras can be used to great effect to see if mice are present. Just bait, and wait...

Again, if using trail cameras, peanut butter and raisins are good bait. Cats don't tend care for these so leaves the site alone, but foxes apparently love it and of course, most small mammals will take any opportunity. Peanuts can attract squirrels and badgers, dog food and dried mealworms will also attract hedgehogs, however dog food is also likely to attract cats so it might be an idea to hide the bait in a box where cats can't get access! As the season progresses we will work on a post on how to use camera trapping to record wildlife, so stay tuned.

Footprint tunnel insert with the ink pads at the entrances and the bait in the middle.

You can also check for small mammals including Wood Mouse in your garden using a footprint tunnel! These are messy things but can made easily enough and be fun to check. A quick internet search will let you know how to make one. Use ink powder mixed with vegetable oil (won't harm the animals) on the 'ink pads' and just plain printer paper for the impressions, bait it with peanut butter, oats and peanuts and wait to see what visits! You can also place a camera in the tunnel if you want to actually see what's been visiting, as the footprints of various small mammals can be very hard to tell apart...

A little known fact to finish off is that bumblebee queens favour old mouse nesting sites for their nests, so they hone in on the smell of mice when they search for nest sites. So if you do find an old bit of a mouse nest in your garage or shed, use it to make a bumblebee nest to help the bees! :)

On the trail of the red squirrel

Squirel (Sciurus sp.) eaten spruce in the grounds of Haddo House. Some cones appear to have been subsequently eaten by wood mouse (Apodemus sylvaticus) 

With some time to spare yesterday in the grounds of Haddo House, I opportunistically found a quiet looking path adjacent to a tree plantation to slowly creep past looking for wild mammals and their field signs.

There is a very obvious clue to amateur trackers of any skill level that red squirrels (Sciurus vulgaris) use the grounds at Haddo -  there are road signs along the drive to the car park which state "Kill your speed NOT a red squirrel."

Following a mammal path under a canopy of spruce trees (with the occasional beech tree), I quickly found an abundance of spruce cones which displayed clear squirrel feeding signs on the woodland floor and on tree stumps.

Squirrels like to sit on a tree stump or mound whilst eating for a good view for predators. Around a third to half of the cones were found on top this stump already, whilst the others were found within around 1.5 metres or so around the stump and placed on top of the stump for the photo just to give an impression of the density of feeding signs in one small space.

Some of the spruce cones  have probably also been eaten by another species after the squirrels! Cones which have been fed on by squirrels alone have frayed ends where the scales have been removed. Wood mouse (Apodemus sylvaticus) will often feed on the cone after the squirrel, removing ragged and frayed ends and removing the tip of the base of the cone leaving a rounded base. The mice often move the cones to a more concealed place to feed on them.

Encouraged by the abundance of squirrel feeding signs, my attention changed from looking at the ground to looking into the canopy for squirrel dreys (their nests). Dreys are constructed from twigs and leaves and are almost spherical (or flattened to be wider than tall). They are usually around 25 to 50 cm in diameter (football size and larger) and normally found against the trunk of the tree (held up from where a branch leaves the trunk) from around 6 metres above ground upwards, though they can also be at a fork in branches.

The darker object is approximately football sized and is a squirrel (Sciurus sp.) drey. Seen in the grounds of Haddo House

The squirrel (Sciurus sp.) drey is the darker object behind many living branches and twigs in the forefront. Seen in the grounds of Haddo House

Crow and magpie nests can be superficially similar in appearance but tend to be found further from the trunk and are usually made of dead twigs without leaves.

A squirrel may use three, four or occasionally more dreys in their territory. Reds and greys are both also known to use more open saucer like dreys during the summer as resting places. I could not decide if another structure that I saw in the woodland was one of those or just an old drey which had started as a spherical form and fallen apart.

Red squirrel (Sciurus vulgaris) and grey squirrel (Sciurus carolinensis) feeding signs cannot be told apart and there are no obvious and reliable differences in the appearance of their dreys to tell them apart. Both species may even use the same drey at different times!

Unfortunately the strong wind at the time of the visit made detecting squirrels themselves difficult and survey guidance suggests that they are less active in those conditions anyway. I will take the word of the road signs on the drive and presume that I was looking at the field signs of red squirrels.

Saving Scotland's Red Squirrels is an award winning partnership project led by the Scottish Wildlife Trust and includes Scottish Natural Heritage, Forestry Commission Scotland, Scottish Land and Estates and the Red Squirrel Survival Trust. It is directed at conserving our native red squirrel and managing the grey squirrels which threaten the reds through competition and disease. SSRS welcome records of sightings of both species to help target efforts where they can make the greatest difference.