20th May 2021

Positive signs for Britain's bat species

Five of Britain’s 17 breeding bat species are showing positive signs of population increases while another six species appear to be stable, according to the latest results from the National Bat Monitoring Programme. None of the 11 species monitored showed any signs of declining.

The National Bat Monitoring Programme [NBMP] report published today (which you an access here) led by the Bat Conservation Trust, presents the 2020 results of an annual 20+ year citizen science programme.

The trends reveal that two of Britain’s rarer bats are on rise: the greater horseshoe bat and lesser horseshoe bat; as are the common pipistrelle, soprano pipistrelle and Natterer’s bat.

It also appears that Daubenton’s bat, whiskered/Brandt's bat, noctule, serotine and brown long-eared bat populations have been stable in Britain over the last 20 years.

Philip Briggs, Monitoring Manager at the Bat Conservation Trust, said: “No species for which we produce population trends are considered to have declined significantly since we began monitoring. While the data indicate that bat species we monitor are stable or recovering, it should be remembered that these trends reflect relatively recent changes in bat populations.

“Historically, there were significant declines in bat populations throughout the 20th century. The new trends suggest current legislation and conservation actions to protect them are proving successful, and it is vitally important this continues.”

The NBMP is an annual series of bat surveys undertaken by thousands of dedicated volunteers. Four long-term monitoring methods were used to produce the population trends: roost and hibernation counts, plus field and waterway surveys across a total of 1,337 sites, involving 850 volunteers. Separately, 244 volunteers also took part in 586 sunset/sunrise bat surveys in 2020. More than 6,600 sites have been surveyed since the start of the NBMP in 1996, many of them surveyed across multiple years.

The field and waterway surveys involve counting certain bat species along defined transects. The roost counts involve counting bats emerging from summer roosts, while the hibernation surveys involve counting bats present at hibernacula.

Trends are calculated for 11 species in England, five species in Scotland, nine species in Wales, one in Northern Ireland and one at UK level.

Bat recording and site visits were severely restricted by the pandemic in 2020. Compared with 2019, the number of field survey sites counted dropped by 17% and waterway survey sites counted fell by 34%. Surveying of some species was affected more than others, for instance, the number of roosts counted fell 16.7% for serotine and 78% for lesser horseshoe bat. Despite these, there were still enough data to indicate reliable trends.

Why are populations changing?

BCT considers two key factors have had a positive impact on recent bat population increases. The first is a reduction in human disturbance due to wildlife protection laws, and the second is a milder climate. In particular, mild winters and springs appear to have benefitted the horseshoe bat species. The impact of climate change on other UK bat species is less clear.

Historical declines in bat populations dating back to at least the start of the 20th century have been blamed on more intensive farming methods, along with loss of roosting and foraging habitats, persecution, pesticides including the use of toxic timber treatment chemicals within roosts, poor water quality, declines in invertebrate prey groups, development and land-use change and climate change. However, evidence of these drivers is limited.

Bats remain vulnerable to pressures such as landscape change, climate change, development and emerging threats such as new building practices, wind turbines, and light pollution.

The NBMP is run by the Bat Conservation Trust, in partnership with the Joint Nature Conservation Committee, and supported and steered by Natural England, Natural Resources Wales, NatureScot (formerly Scottish Natural Heritage) and Northern Ireland Environment Agency.

The full report is available here.