carried out in the vertical position, that is, after the walls were
completed and not before. One visual clue to look for in a barn to help
put a date to the building would be to look for the use of pegs and
wedges instead of nails. Nails were little used before the 19th century.
Other barns that are worth targeting are those where the original 14th
century barn may have no crevices around the sockets but where a
section of the barn was rebuilt, possibly in the 16th century, the play
that was necessary for construction high up in situ resulted in very open
joints. It is these barns that seem to be so attractive to bats. The
presence of a ridge beam appears to have little relevance to whether
bats will be present or not. Ridge beams only became common after
the mid-18th century.
In the last 18 months, 92 barns have been visited. Of these 49 were
suitable for bats. Valuable time can be wasted by visiting unsuitable
barns. Barns can be targeted more effectively by using very simple
selection criteria. The barns worth visiting are those that are more than
100 years old, those with thick beams, those with a roof (although the
roof covering is irrelevant) and of at least 30 square metres of floor
space. Even barns in a poor state of repair can be used by bats.
Bats are only present in any significant numbers during the summer
months when the females cluster together in a traditional roost to give
birth to their single baby of the year. The bats can sometimes be heard
in June or July by carefully listening for the quiet 'chittering' sounds in
warm weather. Some people describe the sounds as 'electrical'.
Sometimes this is the only way of locating Pipistrelle roosts that are
frequently found in small crevices such as behind wooden cladding, in
window and door frames or between the roof tiles and the roofing felt.
The only other way is to visit at dusk to see if bats emerge. The prize
for the most unusual site goes to a Brown Long-eared roost found
behind a sombrero hanging on a nail in a barn. At other times of year
when the bats are absent during the hibernation period, the only visible
'bat' clues might be a lack of cobwebs and the presence of a smudgy
brown stain within the hollow mortise joints. This staining builds up
over many years from the oil off the fur of the bats. Such staining
would indicate significant use by bats.
A close look at the floor beneath the roost might reveal a few old bat
droppings which are easy to identify. Bat droppings are dark brown or
black and vary in size between 4-8 mm long, the same size or larger
than a mouse dropping. Because the bat droppings consist largely of
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