30 Days Wild – Day 1

I started Day 1 of 30 Days Wild at 2:30am when I set a very early alarm to carry out a bat survey.

Despite the murky conditions, the night had been damp but without rain, and the dawn temperature of 10 degrees was quite suitable for bats to fly in.

The survey didn’t reveal any bats coming back to roost in the building I was watching, but eight common pipistrelle bats flew along a tree-line adjacent to the property around 20 minutes before the sun rose. This is around the time at which they return to roost following a night on the wing, suggesting a roost somewhere nearby.

Bats, to varying degrees, use landscape features such as rivers, streams, woodland edges, hedge lines and trees to navigate through their habitats, between roost sites and foraging habitat. These features can be important to a colony, as removing the connectivity can cause severance between the roost and the foraging habitat, a little like closing a road between your house and the supermarket! The survey suggested the tree line adjacent to the property might be important connectivity for a local colony.

One of the joys of a bat survey is being out and about at an early hour when few other people are about but many creatures are already up and about. The damp night had brought out the slugs and snails, which required care to avoid crunching as they worked their way across the paving as the sky grew lighter. I heard the first bird of the morning at 3:50am, just under an hour before sunrise. A blackbird broke the silence with robin, house sparrow and tits soon joining in the chorus.

Below is a sonogram of one of the pipistrelle bats which were making their way back to roost.

A sonogram of the echolocation calls of a common pipistrelle (Pipistrellus pipistrellus) bat in flight. The bats use these pulses, with a peak energy of 45 kHz in this case, to navigate and catch their prey on the wing. Humans can hear up to around 20 kHz, so this was recorded and made audible using a bat detector which can hear these higher frequencies and convert it into a level which is perceptable to the human ear. If you take out a bat detector on a summer evening, a silent night can soon be revealed in its true nature as the calls of hunting bats clatter across the ultrasound aiwaves!