Additional info on the Geofforys bat

The bat was a male and was caught during a survey of autumn swarming bats near the Sussex coast.

Autumn swarming is a phenomenon which occurs at some (but not all) hibernation sites. Bats fly, sometimes over significant distances, to a hibernation site and fly around the entrance for a while. The name 'swarming' is not entirely appropriate because the number of bats flying at any one time can be quite small.

Males spend longer at swarming sites than females do, so that captures of bats usually show a preponderance of males even though probably similar numbers of females and males are involved overall. The functions of autumn swarming behaviour are not entirely clear, but probably include mating between individuals from different colonies (resulting in reduction of inbreeding), scouting out hibernation sites in advance of winter, and allowing juveniles to locate regularly used hibernation sites.

Bat species involved in this behaviour are the Myotis species, long-eared bats, Barbastelles and horseshoe bats. Recent work in Bedfordshire by the Bat Group has shown that several of our better-used hibernation sites have swarming activity of Natterer's, Daubenton's and Brown Long-Eared Bats and Barbastelles.

Geoffroy's Bat has not previously been recorded in Britain as far as I know, but it is present in coastal regions of northern France and southern Belgium.

The presence of a male at a swarming site in coastal Sussex is therefore not too surprising. Geoffroy's joins a list of European bat species which have been found in mainland Britain on one or more occasions - Kuhl's Pipistrelle, Savi's Pipistrelle, Parti-Coloured Bat, Northern Bat, Greater Mouse-Eared Bat (declared extinct in Britain in 1991, but still regularly recorded as a single male in a hibernation site in Sussex), Pond Bat and European Free-Tailed Bat.

There is no evidence at present of any of these species being resident in Britain. On the other hand, this was exactly the view taken of Nathusius' Pipistrelle until the discovery in the 1990s that it was breeding in both Britain and Ireland (and we have records of flying bats in Bedfordshire). The Alcathoe Bat was even more startling, with no British records until it was found, in 2010, to be present in both Sussex and Yorkshire. Also, with the effects of global warming on bat distribution extremely difficult to predict, it could well be that some European bat species could move into Britain in the next few years.

It's also worth noting that we have evidence of behavioual changes in Myotis bats in Bedfordshire woods very recently - Natterer's Bat, for example, has been notably absent during woodland surveys in the last few weeks at sites where it is usually found very easily. It could be a result of the unusual weather patterns this year, but who knows what to expect in the next few years?

Bob Cornes