Weather: 100% Overcast, quite a dark night; 14degC; occasional spots of rain; little breeze, almost still.
Bats account for about 1/3 of all the mammal species on this planet. They often seem to have had bad PR, yet they are remarkable creatures that are generally beneficial.
In the UK, all of our bat species eat insects and we have 17 species that breed here. If you go for countryside hedgerow walks late on a summer’s evening or watch around your house night light, then you may be lucky enough to see bats flying around. The group of species most likely encountered in these circumstances are the Pipistrelle . These are small fast flying bats with great acrobatic ability, turning quickly to catch midges & the like.
Many bats use ultrasound to echo locate their prey. This sound is too high pitched for human ears to hear (save for a few low notes from Noctules (in the UK) that may be heard by young people with good hearing). This is where a bat detector can be a fun & useful piece of equipment. There are several different types available but that is outside the scope of this article. Suffice to say that the following recordings were made using a frequency division detector linked to my netbook computer. Analysis was done using Batscan v.9 and Audacity v1.3.
A few Pipistrelle facts:
Main food is small insects esp. midges; a Pip can eat 3000 midges in one night
Can live for up to 12 years but 5 years is more common
Typical wingspan is 20cm with a 4cm long body
3 species in UK, Common, Soprano and Nathusius
Typical weight is 6g but may be more
Covered in brown fur, more reddish above & yellowish below
One of the most common bats in Britain
Mating season is Aug – Sept, when males have a territory
Young are born in July and leave the roost within 4 weeks
The following sections may seem a bit techy but I hope there’s a little bit of interest for everyone who might be interested in bats …
Soprano Pipistrelle (Pipistrellus pygmaeus)
Recorded hunting rapidly up and down a mixed woodland edge at just above head height, some 25m from the river. The details of the ultrasonic calls can be seen on the sonogram below:
This recording was made at approximately 10:20pm. Further analysis of the call showed the Peak Frequency to be 54.95kHz +/- 0.05kHz. The pulse repetition rate was measured as varying from 8.75 pulses/s up to 18 pulses/s. The peak frequency analysis can be seen below:
The peak frequency of 54.95kHz is very typical of the Soprano Pipistrelle (average often quoted as 55.5kHz).
To listen to these Soprano Pipistrelle bat sounds …
Common Pipistrelle (Pipistrellus pipistrellus)
Recorded hunting along hedgerow above our hide night light. Lights attract insects at night and this makes it a great zone for bats to hunt in; it’s also a good place for you to watch them. The sonogram below shows how the Common Pip’s call is similar to that of the Soprano Pip but at not quite such a high frequency.
This recording was made at approximately 11:30pm. Further analysis of the call showed the Peak Frequency to be 46.70kHz +/- 0.05kHz. The pulse repetition rate was measured as varying from 7.75 pulses/s up to 14.5 pulses/s. The peak frequency analysis can be seen below:
As previously mentioned the Common Pip’s peak frequency is slightly lower, measured here at 46.70kHz and often quoted to average around 46.5kHz.
To listen to these Common Pipistrelle bat sounds …
The call of Pipistrelle bats is sometimes said to be a ‘hockey stick call’. This is because the call starts at its highest frequency and then falls in pitch whilst gaining power; this creates a sort of hockey stick shape when seen in a detailed sonogram , as below:
A Noctule Bat was also recorded in concert with the Pipistrelles but a clean solo recording was not made.