Friday 15 November 2019

Are there any bats on Skomer?

Hi everyone, it’s LTV Rob here! I’ve been off the island for just over 4 weeks now and am missing it a lot, so I thought I’d give you an update of the project I carried out whilst there.
Abseiling into caves for seal monitoring gave me an opportunity to check out potential sites for bat roosts.
One of the animal groups on Skomer that really intrigued me from the outset were bats. With no trees on the island, there appears to be little suitable roosting habitat – so are there bats there? The most recent survey of the island was conducted in 2014, but this was only at The Farm so I was keen to look at activity across the island.
I used an SD1 recorder for the study. These amazing bits of kit can be pre-programmed to record at certain times of day. During active hours, the recorders ‘listen’ for sounds of certain frequencies. When it identifies what it thinks is a bat it records a sound-bite which can then be downloaded later. These recordings are viewed on spectrograms which are visual representations of the calls. Each species has a unique call shape which allows us to tell them apart.
If you visited the island from July to September, you might have noticed my bat detector setup – it looked a bit like some sort of NASA Moon lander! The microphone was tied to an old tripod which meant I could set it up at different locations on the island – The Farm, Moorey Mere, North Pond, North Haven, North Haven Slip, on the main track towards the courtyard and overlooking The Lantern, a large cave system on the very east of the island. I left the recorder for several days at each site and then collected it in to see what we’d got…
The bat detector set up at the Farm

The detector enjoyed some nice views of Middleholm from the 'Lantern' (and strong winds too!)

Over the 7 recording sites, 380 bat recordings were obtained. 6 species were identified with confidence: Common Pipistrelle, Soprano Pipistrelle, Leislers, Noctule, Serotine and Greater Horseshoes. Barbastelle and Grey Long-eared bats were also suspected. This is a good result for Skomer as it suggests that bat diversity is stable. Activity varied between sites for each species, which suggests that species are utilising different areas of the island.
Perhaps the most exciting finding is that of Greater Horseshoe bats! This rare cave-roosting species has declined nationally by over 90% in the last 100 years and is restricted largely to a few populations 
in south-west England and Wales. This is partly due to the intensive use of pesticides which are reducing prey availability. 58 recordings of Greater Horseshoes were taken across the island, which is higher activity than was seen in 2014 – this could suggest that Greater Horseshoe numbers are on the rise on Skomer, which is very encouraging. Islands like Skomer, which is pesticide free, are evidently a natural stronghold for them!
Greater Horseshoe bat (source: Bat Conservation Trust 2010)

A spectrogram of the Greater other species call at 80kHz so I knew immediately what it was!

This project highlighted that there is high bat activity on Skomer and that species activity varied between different habitats on the island. More work is needed to understand how each species is using the island so watch this space! In the meantime, next time you visit Skomer think about these flying mammals which are hidden away during the day and come out to join the Manx Shearwaters after dark…
Thank you for reading my batty ramblings!
Rob (Skomer LTV 2019)