Two recent grisly discoveries have set alarm bells ringing for a rare bat species found in Jersey.
Named after their defining feature, grey long-eared bats are among the UK’s rarest, with an estimated population of around just 1,000, who have been red-listed as a species at risk of extinction. Little is known about the species as a result.
However, in Jersey, such bats are the second most encountered of the island's 18 species, with up to 250 estimated to be on-island.
As a result, Jersey offers an important opportunity for research – something which, for the past four years, has been led locally by Piers Sangan of Sangan Island Conservation, which runs the Jersey Grey Long-eared Project to capture data about and ultimately work to protect the population.
Pictured: Piers Sangan carrying out research for the Jersey Grey Long-eared Project.
While many threats to the species, such as habitat loss, are known, Piers explained that two recent discoveries of dozens of dead bats suggested that climate change might have a role to play too.
After noticing that population numbers were falling far short of expectations by around 30, the group "knew something was wrong" and decided to investigate. After receiving funding from the Howard Davis Farm Trust, they were recently able to acquire the necessary scaffolding to be able to climb up to a roost in a local Methodist chapel.
Once inside, the team found clear evidence of what Piers described as a "significant mortality event."
Warning distressing images.— Piers Sangan ???????????? (@PRSangan) November 1, 2022
This is unfortunately the impact of a heatwave in summer and not how we want to see an entire years recruitment to our largest Grey long-eared maternity roost. @_BCT_ @Mammal_Society #ecology #bats #Jersey pic.twitter.com/IfTi6jdJ7a
In total, they found 42 carcasses of grey long-eared bats – 33 of which were thought to have been juveniles, who were on the cusp of being able to start flying./p>
Piers explained that the number, by the team's estimates, represented 100% of this year's "recruitment from that roost" – in other words, none of the bats born in that roost survived.
It is unclear exactly what caused the deaths. However, the current working assumption is that the deaths were caused by the summer heatwave with the juvenile bats stuck inside the roost in the high temperatures and dying as a result.
Sadly, Piers confirmed, this was "not an isolated event".
After checking a smaller maternity roost, they found a "similar situation".
"The second roost is much smaller but initial results indicate a similar percentage loss and again most of the deceased were juveniles," Piers said, noting that his team will be "continuing to visit other sites to determine the extent of the impact on the island population."
This event is not entirely unprecedented. Heatwaves do happen and have produced similar grisly results in the past. However, after a warmest-on-record summer, there are concerns that the effects of climate change may see more heatwaves in future and that the bat populations will struggle to recover.
Mr Sangan said he was extremely grateful to Howard Davis Farm Trust for helping fund access to the roost, and to Jersey Methodist community and the National Trust for Jersey, who have been assisting in the Jersey Grey Long-eared Project research over the years without which their research to date would not have been possible.
The sad discoveries, he said, "highlight the importance of the work carried out by the Jersey Grey Long-eared Project to monitor this species and the impact our changing climate, development pressures and changing habitats are having on these key indicator species."
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