Caves and Swallets - Gower - page 282

FIG 160. Map of Llethrid Swallet, showing the extensive nature of the caverns. (Joint Nature Conservation Commit-
tee)
CAVES AND THEIR WILDLIFE
Overahundredspeciesofinvertebrateanimalshavebeenrecordedasmaintainingpermanentpopulations
in British caves, while other species such as bats and moths use caves regularly as temporary shelters.
Animals using caves can therefore be divided into different categories depending on the use they make of
thecave.Someanimalsspendonlypartoftheirlivesincaves(trogloxenes),whileothers,althoughoccur-
ring elsewhere, are able to live in caves permanently (troglophiles) and some are only found underground
(troglobites). In addition to the use they make of the cave it is also possible to categorise animals based
on the type of habitat they occupy, the so-called 'threshold fauna' living in the zone between the entrance
and the limit of light penetration and the 'dark-zone fauna' living where there is no natural light.
ThemaininvestigationsoftheanimalsoftheGowercaveswerecarriedoutinthelate1970sandearly
1980sbyGeoffJeffersonfromtheZoologyDepartmentofUniversityCollege,Cardiff.Sincethentheob-
servations have come mainly from cavers rather than biologists and there is a real need for further work.
ANIMALS OF THE THRESHOLD
The animals most frequently associated with caves, in the public mind at least, are bats. The peninsula
is special as it is one of the few limestone areas with both species of horseshoe bats. Greater horseshoe
bat and lesser horseshoe bat occur in a number of the caves and form an important link between the ex-
ternal and internal ecosystems. Usually present in the threshold area, they also penetrate into the dark
zone. Lesser horseshoes are a particularly Welsh species, thriving in Gower as well as anywhere else in
the world. Greater horseshoes, in contrast, are at the northwestern limit of their range here. They are,
however, particularly faithful to suitable roosts and will continue to use them for many generations (Fig.
161). But seeing them in the same place, year after year, can create an air of familiarity that masks their
rarity and vulnerability, and they are in fact probably the least abundant of the Gower bats. Winter mon-
itoring suggests there may be less than fifty of these bats in Gower, but this figure may be misleading
because, despite their large size, they can be very secretive. Bats using the caves are mainly adult and
immature bats less than four years old. The occasional record of younger bats suggests that they breed
in the area, but no nursery site has yet been found. Some of the caves are 'male sites', where a bat may