Easy Pickings for Long-eared Bats...

This week I had the opportunity to look for bats at the usual roost site, and seeing as it gets dark by about 5pm these days, there was no choice but to go in the dark. November is usually a time of reduced activity for bats, and so there was a good chance that some would still be in the roost despite it being dark out side. The roost was the old barn that I have been monitoring for many years, as there are usually two or three species present. The bats use the barn differently throughout the the year, during the summer they are mainly in the roof, but during the spring, autumn and winter they roost at mid or ground level, where the temperature is more stable.

Their roosting habits have been perfectly illustrated in a study that a friend Izabel Phillips did exploring the effects of temperature and humidity on bat activity. Izabel monitored how common pipistrelle Pipistrellus pipistrellus and brown long-eared bats Plecotus auritus used the barn over the course of a year. She recorded numbers of bats, their respective roosting locations and the temperature and humidity within the barn. This is summarised in an extract from her study, below.

In this image the dark spots represent the brown long-eareds and the pale spots common pipistrelles. It can be seen how bats move to the lower levels of the barn outside of the maternity period, but utilise the roof area in the summer. The pips don't breed in the barn and are absent from May through to August, whereas the long-eareds remain in the barn all year. 

On entering the barn a brown long-eared was picked up on the bat detector immediately. It was flying around in the more open (eastern) part of the barn, and soon settled on the brickwork at the apex of the eastern wall. A second brown long-eared was recorded in the apex of the roof at the western end, this bat was awake but still looked quite sleepy. It was settled next to a daddy long-legs spider Pholcus phalangioides and a herald moth Scoliopteryx libatrix, so there were some easy pickings for when it woke up!

Brown long-eared Bat with Daddy long-legs spider and Herald Moth

There were of course other easy picking throughout the barn, as well as the herald moth, small tortoiseshell and peacock butterflies were present. Judging by the number of butterfly wings lying around, it appears that the bats have been taking advantage of this 'in house' food source. It is interesting how they would find these moths and butterflies as long-eared bats usually feed by gleaning their prey at close quarters within dense foliage. Their prey would normally be moving but these moths and butterflies are clearly hibernating.

Brown long-eared Bats - Hook Barn

Brown long-eared bats are one of my favourite bat species, they are not rare, but because of their quiet echolocation they can be very easily overlooked. In the UK there are two long-eared bat species, brown, which is common and widespread and grey P. austriacus, which is extremely rare and restricted to the extreme south/south-west of the UK and the Isle of Wight. Both species have large ears which they use to listen for their prey. They tend to feed on moths, such as large yellow underwings, and there have been some interesting evolutionary battles going on between this moth species and the and the long-eareds.

A torpid brown long-eared Bat

When torpid long-eared bats can lose body temperature through their large ears, but to combat this they tuck their ears behind their wings. The image above shows a torpid bat and the those long ears clearly tucked behind the wing membrane. The mild weather conditions have probably prevented these two bats from entering hibination yet. Whilst in the barn we also recorded single serotine and common pipistrelle, these two bats were still asleep and appeared torpid. I suspect the cold overnight temperatures may have triggered these bats to enter torpor, but the long-eareds are perhaps more tolerant of colder temperatures.