During the 1990s bat experts realised for the first time that not all Pipistrelle bats occuring in Britain were the same. Close examination and the use of bat detectors confirmed that there were two distinct species which are now known as Common Pipistrelle and Soprano Pipistrelle. Both are widely found in North Yorkshire. More recently, a third species has been discovered in the county - Nathusius' Pipistrelle.
This is the bat you are most likely to encounter in the county.
These tiny bats weigh only 5g and will fit into a matchbox with their wings folded. Their fur is a dark brown colour and their faces are usually black. The peak echolocation frequency is 45kHz. Common Pipistrelle bats eat a range of small insects such as midges.
Colonies of Common Pipistrelle bats occur in most towns and villages, often tucked away in the soffit of a house, under the tiles or in the cavity wall. Although a roost may contain several hundred bats, an average maternity roost supports 30-100 individual females. Males mostly live individually, or in small groups. A maternity colony may use several roosting sites during the course of a summer, sometimes moving suddenly to a new location. In winter small numbers may be found hibernating in house soffits, crevices in old disused barns and miscellaneous other places, but rarely in caves.
The distribution map below shows the ubiquitous distribution of this species. The gaps probably indicate more where people haven't looked for bats than an absence of this species!
The related Soprano Pipistrelle is very similar to the Common Pipistrelle, but with a pinkish face. Its peak echolocation frequency is rather higher, at around 55kHz.
Soprano Pipistrelle bats also feed on a range of small insects, but prefer insects that are associated with water. Therefore, whilst roosts are generally in similar crevices to those of Common Pipistrelles, roost sites are usually located close to water. On the map below, you may be able to see that the distribution of this species closely follows the county's main river corridors.
Until quite recent times this slighly larger species of Pipistrelle was thought to be just an occasional visitor to the UK. However, a number of roosts have now been found in Britain, including one in the North York Moors National Park. There have also been other reports of bats in flight being located by bat detectors, so there could be more roosts out there. However, it is likely to remain one of the county's rarest species.
Knowledge of bat migration in the UK is limited, but this is probably one of our most migratory bats as a number of individuals have turned up in one rather unlikely setting - North Sea oil rigs!