Sunset bat emergence visit

After another fabulously warm and sunny day and a clear evening promised, I thought I would grab the opportunity to pop along to a house near to the rail crossing in Lucks Lane and check out the Soprano Pipistrelle (Pipistrellus pygmaeus) roost in the west facing gable end of the house. This is a roost I ‘discovered’ about 8 years ago on a springtime evening stroll along the lane. Passing beneath the overhanging gable I heard bats chattering just before they emerged from the roost. Since then I have visited the roost in May / June, when time allows.

West facing gable end of the house where the bats roost.

The owner is aware that bats roost in the house during spring and early summer period and takes part in a national bat roost survey, run every June by the Bat Conservation Trust, for this is an important bat maternity roost, where baby soprano pipistrelle bats are born.

Soprano pipistrelle bats were only recognised a separate species in 1990, up to then the two ‘pip’ species in the UK were thought to be just one species. As its easier, I tend to call them ‘Pip 55’s’ for they produce their best sounds at a sound level of 55,000 HTZ, whereas the common pipistrelle bats are best heard at 45,000 HTZ and so are known as ‘PIP 45’s’.

Soprano pipistrelle bat (Wikipedia)

The human ear can hear up to about 20,000 HTZ. So how can you hear bats which are above our hearing range ? You use a bat detector ! This is a ‘magic’ box which reduces the sound by a factor of 10, so that we can hear the sound bats are making when they are flying. All bats in the UK fly mainly at night and feed upon insects. They navigate the night time skies using sonar, in effect shouting and waiting for the echo to return and using their very sensitive ears create a soundscape of their environment. Each of the 17 bat species in the UK makes a separate and recognisable sound and like bird song once you get your ear tuned in you can identify the different bats flying around in the sky,  between dusk and dawn.

A simple bat detector

So back to my spur of the moment emergence visit, what was involved ? All bats species in the UK are legally protected, so surveying must take place in a manner which causes them no harm. Actually it’s really pretty simple. I just drove round to the house and sat outside in the car with the window wound down, the bat detector switched on and waited for any bats to emerge. Timing is important so I arrived 10 minutes before sunset. Pip 55’s usually emerge around 20 mins after sunset, but its best to be early !

Sunset time was 20.24 on Tuesday 3^rd May and at 20.31 out popped the first Pip 55 bat and flew off in a southerly direction. The bat emerged from a gap in the soffit at the top of the gable end.  Pip bats are pretty small so any gap which is at least 8-10 mm wide will be enough. As well as hearing the bat I also saw it as the light was still good at that time. It was another 16 minutes before any more emerged, but at 20.47, after a bit of pre-flight chatter two more Pip 55’s popped out and flew along the lane towards the railway crossing. A minute later three more emerged, again flying in the same direction. Pip 55’s like to feed on insects around areas of water, rivers, streams, ponds, lakes etc and there are fishing lakes nearby and the River Medway about 2 Km away, so it’s not that far to travel for a  bat snack! The last three bats emerged at 20.51 and then that was it for the night, a total of nine Soprano Pipistrelle bats.

Pipistrelle bat in flight (Wikipedia)

In recent years the Pip 55’s have tended to meet up in this house, prior to finding additional local maternity roosts, so I am expecting numbers to rise over the next 4 – 5 weeks. I will post further reports in later in May / June, to report progress for the 2016 bat breeding season, but it’s great to know that the bats are still using this house as a roost.