September Nature's Calendar

This year, a species of bat never seen before in the UK was discovered living in caves in Yorkshire and Sussex. The Alcathoe bat is the latest addition to bats living in the UK. That the bat has been found in the north and south of the country indicates that it may be present in other parts, but it may have gone undetected due to its similarity to the whiskered bat and the Brandt's bat. The Alcathoe bat brings the total number of bats in the UK to 17, making bats the most diverse of Britain's mammals.

How bats evolved is subject to debate but the most likely suggestion is that they evolved from a tree climbing, shrew-like mammal. The earliest fossil of an insect eating bat is 50 million years old, and is very similar to those found today, suggesting that bats had already largely evolved by then. Bats have evolved to be well suited to their environment, with their wings being their most impressive feature. Like humans, they have four fingers and a thumb on each hand. The fingers are very long and very thin, with the wing membrane stretched between them. The thumb is small and has a claw that is used for gripping when the bat is at rest.

Although bats can see, they use echolocation to find their prey and avoid obstacles in the dark. The bat emits a very loud and short sound. They listen for the echo that bounces back when it hits an object. The bat can tell how far away the object is by the amount of time it takes for them to hear the echo. Some bats use their mouths to shout out the noises. Others snort the sounds out through their nostrils; bats that do this tend to have strange shaped noses to help them direct the sound. In the UK, horseshoe bats echolocate through their noses. Different bats use different sound frequencies to echolocate, this means we can use bat detectors to help identify the different species we see on a bat walk.

Bats are nocturnal and roost during the daytime. Their roost sites need to be sheltered and away from predators. Typically they will choose holes in trees, caves, roof spaces or niches in buildings as roosting sites. Temperature and humidity are important factors when bats choose a site. Females, for example, will choose hot places when they are pregnant as bat embryos develop slowly when cold.

In temperate areas, such as the UK, the cold weather of winter months reduces the amount of insect food available. To cope with this bats hibernate. They can survive for months in this state on the stores of fat they have built up in their body. Once in hibernation it takes a bat about an hour to revert back to it's normal state. For this reason they choose even more hidden places than for their summer roosts. During hibernation, their heart beat falls to about 20 beats a minute and breathing can slow to only five breaths a minute. Bats won't hibernate for the whole of the winter. Occasionally they will wake up to feed to find a new roosting site.

Although not rare, our local bats are still spectacular, protected and threatened, and there is hope of some rarer species making the Elmbridge countryside their home. Surrey Wildlife Trust reported a rare Bechstein's bat roosting near Ockley in 2009. Those more likely to be seen locally include the graceful Daubenton's bat which can be seen skimming the surface of the River Mole and the common pipistrelle in large numbers flying and hunting in the open.

We manage our local countryside sites to encourage bats as well as other animals. Some of our countryside sites and cemeteries have bat boxes. These are particularly important in areas with few natural roosting sites, such as coniferous woodland. Where it is safe to do so we leave old, dying trees to rot slowly to attract insects. Bats may also use the rot holes in the trees for roosting. The remaining stump of the old oak tree that fell in 2009 near the Ledges has been left and will provide a good roosting site.

You can also do your bit by installing bat roosting boxes or by insect friendly gardening. Avoid using chemical pesticides in your garden; instead encourage natural predators such as hoverflies, wasps, ladybirds, lacewings, ground beetles and centipedes. Leave hollow stemmed plants as shelter for ladybirds, leave heaps of dead leaves and brushwood undisturbed for hedgehogs and provide regular food and water for garden birds as they are also effective predators.

Why not come on our next bat walk on Friday 10 September, 7.15 pm at Horseshoe Clump car park, and admire their aerial acrobatics for yourself!

For more information on what you can see at this time of year contact the |Countryside Team.