September brings a lively showcase of Britain’s smallest and most secretive mammals. Harvest mice balance delicately on wheat and barley, while field mice scramble for blackberries and dormice raid apple stores. Water voles, betrayed by a sudden ‘plop’ into the water, are on the move to claim new territories. Above ground, squirrels dash past with nuts stuffed in their mouths, while stoats and weasels stalk the glut of young prey, their movements giving them away. Underground, young moles tirelessly rebuild their winding tunnels, their powerful shoulders heaving the soil into fresh molehills. As dusk falls, the skies come alive with bats – pipistrelles, Daubenton’s and noctules – feasting, courting, and even calling for mates. September is a month of harvest and hidden drama in the mammal world.
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Mammals
Harvest mice are especially fond of wheat and barley grain although they have to survive on insects in hedges if they lose their nests to combine harvesters. Field mice are often seen climbing brambles for blackberries in September but shrews ignore the harvest, preferring slugs and snails. Dormice are not unlike ourselves, being partial this month to cherries and apples. They often find their way into apple boxes, especially if they are being stored in lofts. Voles generally have one of the most harmless of diets. Water voles are content with roots and shoots and bank voles concentrate on nuts and seeds but occasionally will turn to snails. Young water voles are now on the move looking for a stretch of water bank to call their own. Their arrival in a new area can be betrayed by star-shaped tracks in the mud and greenish droppings, although we are usually first alerted by a ‘plop’ as they disappear underwater. Some females may still be giving birth to their last litter this month in nursery burrows which have underwater entrances.
Squirrels are often seen hurrying past with nuts in their mouth this month. They often chose to go far afield to find good hiding places for them. The soft compost in garden pots is too perfect and so consequently their activities and the offending nut are found by many an irate gardener. Even though they relish autumn fruits and seeds they are not above taking a young rabbit. Stoats and weasels, being totally carnivorous, are also not interested in the glut of autumn fruits but are interested in the glut of young mice, voles, rats, rabbits and hares. With an excess of food they will sometimes kill unnecessarily, leaving uneaten corpses near their nests. This month it is quite easy to confuse a young stoat with an adult weasel.
Other than the black tip on the stoat’s tail, which is absent on the weasel’s, they both tend to move differently. Stoats often move in more of a serpentine way compared with the headlong straight dash of weasels. Also weasels have a habit of running with their tail almost vertical, especially if they are about to pounce. Both inhabit old walls but weasels are also fond of railway embankments.
Half of the moles underground now are likely to be juveniles. They are spending half the day repairing or looking for food in their tunnels and half resting. Many of the temporary surface or courting runs are now unused and collapsing. The main tunnels tend to be ten or twelve centimetres below the surface and straight if they are made by males and winding if made by females. We can sometimes get an indication of where they are by any yellowing grass just above them. Any fresh mole hills seen have not been created by a head pushing up through the soil but by the strong, powerfully-built paws which have an extra bone in them to widen their surface area. Their relatively enormous shoulders and deep breast bone carry strong muscles which are also fit for purpose. It is worth remembering the number of molehills seen is not an indication of the size of the mole population.
Bats are still to be seen at dawn and dusk especially in places where there are still plenty of emerging insects e.g. canals, sewage works, rivers and old traditional farms. Places where a number of different species can be seen with a good chance of some rarities include Barnes Wetland centre, Highgate wood, Wimbledon common and the Box Hill area.
At Barnes Wetland centre and nearby Barnes common a variety of bats may be seen i.e. Common, Soprano and Nathusius’s pipistrelles. Daubenton’s bat is frequently seen hovering over the water at Queensmere on Wimbledon common. A good spot to see Noctule bats is at Berwick ponds.
Wherever there are good patches of ancient woodland it is worth looking out for Natterer’s and also long-eared bats. Serotine and Leisler’s bats are both recorded from Windsor forest.
Like other mammals, bats have their favourite foods e.g. Brown long-eared bats are particularly fond of yellow underwing moths and noctules are partial to flying beetles. Consequently, habitat can often give a clue to what bat might be flying there. The slopes of Box hill going down to the river Mole is always a good place to visit and in September the Brown long-eared bats there may even be making audible sounds.
If bats are heard this month it is likely that they are either courting, mating or swarming. Males, rather than go looking for females, tend to stay near or in their roosts and call out for females to join them. This has the effect of driving off any other less dominant males and consequently males can be found in their roost with a small harem of several different females. Mating can be a noisy affair with a lot of screeching from the male before he holds the female by the neck and then mounts her. Congress may take half an hour or more and is usually followed by copious washing and grooming.
