Caves and Swallets - Gower - page 283

live alone for much of the year, although outside the breeding season they may be accompanied by non-
breeding animals. Mating generally takes place in the autumn and winter, when the males are joined by
females, who may mate with a number of individuals.
FIG 161. Greater horseshoe bat occurs in a number of the Gower caves. (Melvin Grey)
Although both species of horseshoe bats were originally cave dwellers, and the Gower caves are used
as hibernation sites, few animals now use them in summer. Anecdotal reports from the middle of the last
century suggest that some caves at that time had large populations of both greater and lesser horseshoes
and may also have housed nursery clusters. These clusters were groups of females, numbering several
hundred individuals, which gathered in caves where their combined body heat would raise the temperat-
urehighenoughtoreartheiryoung.DuetothedramaticdeclineinthepopulationsofBritishbatsoverthe
lastfiftyyears,thenumbersofbatsarenowtoolowforcavestobeusedasbreedingsites.Summercolon-
ies of lesser horseshoes are found instead in the roofs of the large houses and stable blocks, the breeding
females choosing sites with large entrance holes that give access to open roof spaces warmed by the sun.
The recent discovery of greater and lesser horseshoes in the underfloor area of a modern holiday chalet
in the peninsula is an indication of the ability of bats to adapt to a changing world, if they are given the
opportunity.
Newstudieshaverevealedapreviouslyunknownuseofcavesbybats,knownasswarming.Swarming
occurs in late summer and early autumn and can involve large numbers, sometimes hundreds, of bats.
They arrive at a cave after dark, enter it and disperse within it, and most are gone by the following morn-
ing. The phenomenon may be repeated the following night, but not necessarily by the same bats, which
mayhavemovedontoanothercave.Insomeareasbatshavebeenmarkedandhavebeenfoundswarming
at another site 30 miles (48 kilometres) away, and it is suspected that greater distances may be involved.
The purpose of the behaviour is not yet understood, although the identification of hibernation sites and
mating may be part of the answer. It would be worth surveying the Gower caves to check for this beha-
viour, as many caves elsewhere, previously dismissed as of little or no interest, have been found to have
significant levels of bat activity when checked at the right time of year.