April is the start of the bat survey calendar. After a winter of hibernation, bats are waking up and beginning to feed up for the season. Bats mate in the autumn and use seasonal delayed implantation (also called embryonic obligate diapause, a technique for ensuring that young are born during times of plentiful food) during the winter, allowing themselves to become pregnant once food is abundant.
(I once had a female bat come into care due to injury in the winter. Some weeks later she gave birth to a pup, and knowing bat gestation periods, I worked out that she allowed fertilization to take place within 48 hours of being exposed to warm temperatures and ample food!)
Saturday was the first of the BrumBats bat box checks for 2016, and though it was in a short but sharp drop in temperature (It snowed at 7am!), we still found bats. Four noctules were found in one of the Schwegler 1FF bat boxes – the same box we found a single noctule hibernating in when we did our box maintenance in January.
As bats are a European Protected Species, it is illegal to disturb them – this means even torches, so at least a Class 1 survey licence from Natural England is required if you just want to use a torch to shine up to check if they are occupied, and a Class 2 survey licence to check bat boxes and handle bats.
The bats are gently removed from the box and placed into cotton bags to reduce stress. We keep handling to a minimum, taking some basic biometrics: forearm length using vernier calipers or wing rules, and weight using spring scales – these measurements give us an idea of the health of the bats. Our four noctules all appeared to be in great health!
This first survey is a great start to the bat box season. We have two new bat box schemes so will hopefully have info on their success soon! All the bat records feed into the Batlas Project, helping us to get a clearer picture of the distribution of bats in our county.