Specieswatch: rare bat may have been in UK for decades

An elusive British mammal, the tiny bat Nathusius’ pipistrelle (Pipistrellus nathusii), may be more widespread and numerous than previously thought.

Sometimes described as a rare visitor or a new coloniser because of climate change, it may have been here decades but had gone undetected.

Perhaps this is because the species tends to avoid humans and lives in woods on the edge of lakes where insects are plentiful. It is also a featherweight, a maximum of 15g, the same as a 50p coin.

Related: Batspotting for beginners - four British bats

All British bats are fragile-looking creatures, most often seen by humans on warm summer evenings at dusk, although they are often unnoticed when out hunting. They even emerge in the winter if it is warm enough.

Now that bat detectorists know this species of pipistrelle is resident in the UK, sightings are being reported not just in the south-east of England but in Anglesey, Northern Ireland, Scotland and Cornwall.

In the summer breeding season males have territories, the successful ones have a harem of up to 10 females, while others manage only two or three.

Perhaps the most extraordinary feature is that they migrate across the North Sea. One that was ringed at Blagdon Lake, near Bristol, was discovered in the Netherlands three years later, 370 miles away.