Caves and Swallets - Gower - page 284

Lesser horseshoes are known to use at least eight buildings in Gower as nursery roosts, but there are
likely to be a number of other sites that have not yet been discovered. There may be no more than 2,000
individuals in total. This is still quite a fragile population and the trend to convert outbuildings and barns
into dwellings will increase the pressures on this species and limit population growth. The greatest mys-
teryregardingthebatsiswherethemajoritygowhentheyarenotinthenurseryroosts.Whiletheyarefre-
quently encountered in the caves, there are only small numbers and the majority of individuals examined
are males. Perhaps the mild climate means that they remain active for much of the winter and only retreat
to an underground location in extreme weather. Bats can be very active in the winter, feeding over the
coastal slopes and in the sheltered valleys. Alternatively perhaps they leave the peninsula for more suit-
able hibernation sites. Several of the caves within the Parkmill and Llethrid valleys, such as Cathole, are
nevertheless used as hibernation sites by Daubenton's bat Myotis daubentonii , whiskered bats and Natter-
er's bats. The presence of Daubenton's bat is particularly interesting as they are known as the water bat
and feed almost exclusively on insects on the surface of the water. At first sight the peninsula would not
appear to be an ideal location for this species, as there are relatively few lakes and ponds and many of the
streams are well covered by vegetation.
Some exposed coastal caves are also frequented, surprisingly regularly, by bats of the genus Myotis
that would normally be more associated with woodlands. Sea caves are under-surveyed and may prove
moreimportantforbatrooststhanispresentlyrealised.Therearenohedges,orotherobvious'flightline'
features, to the caves. Perhaps these sites are traditional locations that may have once had more suitable
vegetated links, orbats are migrating along the coast using the peninsula as a landfall. Greater horseshoes
will, however, cross open water and have been found on a number of islands. There has even been a re-
port from a bird-ringer on Lundy of a horseshoe being caught in the nets there. Clearly a dependence on
linear landscape features breaks down for some journeys. New species of bats do appear to be colonising
Gower, and in the winter of 2000/01 an unusual bat was seen in a crevice on Great Tor, between Oxwich
and Three Cliff Bay. It could not be extracted, but appeared to be a species of pipistrelle and was ori-
ginally thought to be a Nathusius' pipistrelle Pipistrellus nathusii , a European migrant that has begun to
colonise Britain and which has been found elsewhere in South Wales. Alternatively, it may have been a
Savi's pipistrelle Hypsugo savii , which was recorded the same week elsewhere in Britain, and which has
the same colour and proportions as the bat seen at Great Tor.
Many invertebrates, especially insects, use cave thresholds as overwintering sites. There are two
mothsinBritainthatareparticularlyassociatedwithcaves,thetissuemoth Triphosa dubitata andtheher-
ald moth Scoliopteryx libatrix , and they are often seen settled on the walls or roofs of cave thresholds in
Gower (Fig. 162). The caterpillars feed on vegetation outside the cave, but soon after emerging from the
chrysalistheadultsflyintocaves.Heraldmothsbecomeverytorpidandcanoftenbeseenhighinthedark
zone of the cave covered with beads of moisture, while tissue moths prefer to settle closer to the entrance
and lower down. It appears that a period of suspended development is necessary before the ovaries of the
female can produce eggs. Similarly large numbers of the common mosquito Culex pipiens can be seen
in the caves from September to April. These are females of the autumn generation which have already
mated, but which will not lay their eggs until they have left the cave in spring.