Pipistrelle – Bat Report

Spent a few enjoyable hours recording bat calls last night – here’s a report on some of our insect eating friends, including some recordings to listen to: 

Date: 3rd August 2010 

Sunset: 9:05pm 

Duration: 9:00pm to 12:10am 

Location: Foel Friog  

Weather: 100% Overcast, quite a dark night; 14degC; occasional spots of rain; little breeze, almost still. 

Introduction 

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: 

sop_pip-sonogram-3rdAug2010 

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: 

sop_pip-peakfreqanal-54_9kHz-3rdAug2010 

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. 

com_pip-sonogram-3rdAug2010 

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: 

com_pip-peakfreqanal-46_7kHz-3rdAug2010 

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: 

com-pip-in_detail 

A Noctule Bat was also recorded in concert with the Pipistrelles but a clean solo recording was not made. 

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I hope this has helped to interest you in our British Bats

May I take this moment to suggest Batbox detectors and either NHBS or Alana Ecology as suppliers of wildlife & field equipment; thanks to them for the good service they provide. 

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“Brock” The Eurasian Badger (Meles meles)

The Eurasian Badger (Meles meles) is a shy nocturnal mammal; it is a member of the family Mustelidae. They are opportunistic omnivores who manage to survive on what their environment offers them; more on that later, here’s a picture:

_MG_6915-18Apr09-edit3   Click image for a larger view …

Adult badgers typically weigh 10 or 11 kg and are 75 to 90cm long with a moderate bushy tail of about 20cm. Their distinctive black & white face is easily recognised but sadly the only place that many people will see these beautiful creatures is dead at the side of the road, where many thousands are killed each year.

The UK has an estimated badger population of > 250,000. Badgers live in communal groups of up to 14 but more typically 7 or so. There is a dominant male (boar) who will protect the territory if necessary and one perhaps two breeding females (sows). The size of the territory depends upon the abundance of food but is typically ~200 acres. Badger dispersion is relatively low and contact between neighbouring groups is often low; the Badgers preferring to mark their territory with latrines and avoiding conflict where possible (conflict between rival boars can be quite violent). Preferred ground is woodland & permanent pasture with an abundance of earthworms, their main dietary component. Badgers do not hibernate but their activity levels may fall greatly in times of cold & hardship, at which point 2 or 3 may share a sleeping chamber for warmth.

The picture below of a badger about to squeeze under a fence line, clearly shows its bushy tail:

_MG_6927-23Apr09   Click image for a larger view …

Badgers have an extremely varied diet that follows availability in the different seasons. As previously noted, earthworms provide the bulk of their diet, this is why they pull up grass turf & dig through droppings. A Badger may consume as many as 200 earthworms in one night, indeed earthworms are thought to make up 50% of their diet. Other favourite foods include insects, beetles, berries, roots and nuts; these probably account for a further 40% of the Badger’s diet. If the opportunity arises a Badger may take small animals such as frogs or occasionally a rabbit, rats & hedgehogs may also be taken; these small creatures probably make up the final 10% of Brock’s diet. Other than man, badgers have no natural predators however wolves & bears may kill them in competition. Whilst many are killed on our roads, the main threats to the badger are urbanisation, intensive agriculture & persecution by humans. Badgers live in underground tunnels called ‘setts’ which may be over 100 years old. Human disturbance of a sett can be disastrous.

Badger-Diagram-1b   Click image for a larger view …

Setts are built up by successive generations of badgers. The main sett will be occupied all year around and consist of many meters of tunnels. Deep in the sett will be the breeding chamber where a sow will have her cubs. The chamber will be lined with bedding materials such as dry leaves or grass. It is often possible to see piles of old bedding outside the main sett entrance. The sett will also contain other sleeping chambers where the other community members can rest. Other subsidiary setts may be built around the territory and are most likely to be used when the sow has young cubs & wants peace in the main sett. In an old sett the main area can become quite complex & extensive; GPS readings from our local sett show that from bottom left to top right the sett covers some 57,000 sq. feet of surface. The 425ft length also covers quite a change in elevation, as the GPS profile below shows:

image

If possible badgers prefer to avoid heavy wet clay soils that are not easy to dig in or dry to lie in. A sloped, free draining woodland edge site with easy access to the forage of both grassland & woodland, is probably a Badger family’s ideal real estate.

_MG_0001-25Apr09-edit   Click image for a larger view …

Having mated in spring the sow delays implantation of the embryo for around 9 months. The actual gestation period is a short one of only 7 weeks and the young cubs are born in early spring. The cubs are born blind, often in a litter size of about 3. They are initially dependant upon the sow’s milk. After 6 weeks the cubs’ eyes are open and at 8 weeks they start to venture out from the sett. These first ventures are often in April / May. By 4 months old the cubs will have their full set of teeth and be foraging for themselves. It will take a year for the cubs to reach full maturity and less than half of them will make it.

If you’d like to watch badgers yourself, probably the easiest way is to join your local Badger group, there are many across the UK. You may also be lucky and have badgers that visit your garden to look for scraps; if so, a few peanuts will encourage them no end and you may soon be able to watch them from your house.

Badger Trail   Click image for a larger view …

Many people miss the signs of local badger activity, here are a few things to look out for:

  • Discarded Bedding
  • 5 toed footprints on worn paths
  • Dung heaps & latrines
  • Spoil heaps outside setts
  • Badger hair on fence lines

Below are pictures of a spoil heap and discarded bedding, click either one for a larger view:

Spoil Heap Discarded Bedding

Good luck with your watching; Badgers really are beautiful & fascinating creatures.

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Squirrel Nutkin returns

The local squirrels are in fine and mischievous fettle this spring. The grey squirrel (Sciurus carolinensis) can breed twice per year, with the first mating season beginning in spring. After mating the female will drive the male out of her chosen tree, where she will give birth about 6 weeks later, in a drey on some high branch. The mother will carefully rear her young for about 3 months before chasing out any hangers on and then starting to prepare for her next litter.

Squirrel Portrait   click image for a larger view …

Squirrels can make themselves unpopular with foresters by stripping bark from trees. They do this mainly in spring time to get access to the sweet sap beneath. Mind you, bird feeders are of course a very convenient snack bar, laid on solely for the benefit of the squirrels. Mischievous & playful the grey squirrel was introduced to Britain in 1877 from North America. It is about 30cm long with an extra 20cm of tail and can live for up to 8 years.

Squirrel at Table   click image for a larger view …

Foraging is an extremely important part of a squirrel’s life; in autumn they will bury nuts to save them for the winter. They don’t always remember where they put the nuts and so sometimes help the trees by nicely planting a new tree. It’s quite surprising the rate that these little guys can put away the food, read the rest of this post to see a video demonstrating this:

 

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