Best for Bats

Tuesday 11th September was a fine day, with large clouds of small insects gathering over the river and river banks here and there, and larger insects crowding over bank-side vegetation where there were ripe fruits, with no wind to sweep them away. The evening sky was clear and bright and still light at 20.00 when the bat survey commenced after an impatient wait after the sunset at 19.19. Bats could still be seen by eye, silhouetted against the clear sky, for about 15 minutes but at 20.15 the sky was dark - plunging the riverside into darkness, time to use the bat detector.

Bright moonlight such as this, taken on 22nd July, can put bats off travelling and foraging - but on this night - 11th September, there was only a sliver of light, low over the horizon.

Starting at the base of the bat flyway hedge on the river bank, there were good numbers of Common Pipistrelle bats with some very obvious 'calls' (echolocation signals) from Soprano Pipistrelle bats interrupting them as their foraging flights crossed. Heading for a location where the river widens, some echolocation calls from Daubenton's bats were heard. Characteristically, initially the largest numbers of bats were in the vicinity of the very old riverbank oaks, with the earliest activity noted whilst it was still dusk, from bats emerging from their roosts in cracks  and holes in the old branches. These roosts may well have been used for hundreds of years where an oak could have been damaged by a storm and survived, as oaks do.

The timing has to be just right for recording the presence of bats using a bat detector, as most bats emerge from their roosts at dusk when they use their eyes to  forage, and we use ours to look up and see them darting amongst the tree branches. Later as it grows dark, they 'switch on' their echolocation ability which guides them, taking over from eyesight. Therefore we should not expect to 'hear' bats using a bat detector until it is dark. Bats make audible calls too, when communicating with other bats. 

Habitats that attract foraging  insects are best for bats - streams and rivers sheltered by vegetation with flowering and fruiting plants and sheltered woodland or wild fields and field margins. Bats, like birds and insects, are important pollinators too.