By Iain Porter Sept 2017
In our fourth year of bat monitoring our superb volunteers have notched up 18 surveys across 6 transects (sites or locations), spending over 140 hours monitoring bats around the Quantock Hills.
Bats are fascinating creatures, the only mammal that can truly fly, achieved through the evolution of their arms and hands into wings. In fact their family name is Chiroptera, which means ‘hand wing’. Worldwide there are over 1,200 species of bat the smallest being the Kitti’s hog-nosed bat (often referred to as the bumblebee bat) which is only 3cm long to the largest, the Giant golden-crowned flying fox, with a wingspan of 1.7m and weighing up to 2kg.
In the UK there are 18 resident species, Somerset is very lucky in that it has records of 16 of the 18 species, the latest to be found was only in 2010 when a Leisler’s bat was found in Taunton. All UK bat species are classed as microbats which tend to be the smaller species. The most common of the UK Bats is the Common pipistrelle, which weighs only 5grams and can eat an amazing 3,000 tiny insects in one night.
What I find fascinating is the different adaptations bats have developed to perfect their hunting style. An example is the Brown Long eared bat which has broad wings and tail allowing them to fly slowly amongst foliage, picking insects off of leaves and barks. The Daubenton bat usually takes insects from close to the water and has even been seen taking prey directly from the water surface. They have large feet which they use as a gaff or they will use their tail membrane as a scoop.
The other fascinating thing about bats is how they manage to find their way at night. All bats can see, almost as well as humans, but at night when light levels are low bat use echolocation to find their way around. Echolocation works in a similar way to sonar, where a bat will make a call as they fly and listen to the returning echoes to build up a sonic map of their surroundings. The bat will be able to tell how far aware something is by how long it takes the sound to return to them.
These calls are pitched at a frequency too high for adult humans to hear – we can hear frequencies from 20Hz (cycles per second) to 20,000Hz or 20KHz. Different bat species will ‘call’ at different frequencies, with Noctules calling around 20KHz and Lesser Horseshoe bats calling up to 110KHz. The reason for bats to emit their echolocation calls at such high frequencies is to get detailed echoes from small insects. The only downside is that high frequencies do not carry far in air so the bat has to emit exceptionally loud sounds, with the loudest known bat call exceeding 140 dB. It is just as well that we cannot hear the bats echolocation as the threshold of pain for humans is around 120 dB!
Somerset Bechstein in Hand - Image Bat Conservation Trust Paul Kennedy
So how do we identify different bat species? Well they have different attributes, such as length of the forearm, but it is very rare to get that close to a bat – and illegal unless you have a license. They also have different roosts, flight patterns and emergence time after dusk (time that they leave their roosts to hunt). But the greatest aid to identification is a bat detector. A bat detector makes the echolocation calls audible to humans and with practice you can recognise the different calls that the different species of bat make.
In the UK bat populations have declined considerably over the last century. This is due to building and development work, loss and degradation of their habitat the loss of commuting routes by road building and removal of hedgerows and threats in the home, such as chemicals and cat attacks. Due to this decline in populations all bats and their roosts are protected by law.
It is due to the national decline in bat populations that we started the bat monitoring programme on the Quantock Hills, as our local knowledge was very limited. We are able to use the findings of the monitoring to inform local management plans and land management as well as feed it into the national monitoring programmes being run by the Bat Conservation Trust and Natural England. Initial results from this summer’s monitoring have been positive with at least nine different species being recorded and significant numbers of calls on all the transects, including nationally rare species such as Lesser Horseshoes and Barbastelle.
All of this could not have happened without the commitment and enthusiasm of our dedicated band of volunteers who come out at unsocial hours throughout the summer, wandering in the dark listening for the elusive calls of one of our most enigmatic night-time creatures.