Tonight I went for a walk with the Herts & Middlesex Wildlife Trust in Harpendon Common. It wasn’t a long walk, but we weren’t there to get the miles in, we were there to find bats!
Bats are not the winged-terrors that Halloween would suggest. Vampire bats do exist in the Americas, not the UK or Transylvania, and their victims of choice aren’t human but equine (must be all the garlic in our spag bols).
We do have a good selection of flying furries over here though as 18 species of microbat bat call the UK home. As they name suggests, microbats are small; they are insectivorous, fly during low light and use echolocation to pinpoint their prey. On the other hand, macrobats are large, eat fruit and love a big of sunshine!
Being a nation full of microbats we have to go out as the sun sets as they rely on the cover of darkness to hunt. They are most active during the summer as insects are abundant, but going for a bat walk during the autumn is not a bad time to spot them as bats are on the look out for mates (and sun sets are at a more school-night-friendly time).
Something amazing that I learnt from Heidi, our Wildlife Trust guide leading the walk, was that bats can delay implantation. This means after mating the female has the ability to retain sperm inside her body for an extended period of time without it fertilising the egg. Only when she’s ready will she let the process be completed. But why would bats do such a thing? With a gestation of only a few weeks it would be detrimental for bats to give birth during the winter. So this process allows her to wait for food densities to be higher so she can regain strength after hibernation and provide amble nutrients to her offspring. Pretty clever right!
Harpendon Common is quite typical of town or village commons around Britain: a large proportion is dedicated to grass, with trees sporadically placed in clumps and one or two very small patches of wood. Due to the habitat, we were told we might see pipistrelle bats that prefer to forage near cover, e.g. hedgerows, and noctule and serotine bats which hunt in open spaces.
To track down our tiny aerial predators we were using devices to detect the high-pitched calls that they use to locate their prey (echolocation). We can’t hear these screams; otherwise a bat walk would be a lot simpler and probably not as enjoyable… Our human ears can pick up frequencies of up to 20,000Hz, whereas the lowest range of bat screeches in the UK are 20-25,000Hz. Different bat species operate on different frequencies, for example the common pipistrelle echolocate at a frequency of 45,000Hz and the aptly named soprano pipistrelle echolocate at 52,000Hz.
Here’s what they sound like when using a bat detector.
The ‘chip chops’ sounds are the bat sending out screams to scan the area for food. When the scream-rate dramatically increases with barely a space in between sounds the bat is close to its prey; if we were talking about a tiger, they would be preparing to pounce. This sound is called the ‘feeding buzz’ and allows the bat to quickly gather detailed information on the movement and whereabouts of their prey allowing them to go in for the kill. Quite beautifully the ‘feeding buzz’ sounds like the bat is blowing a raspberry!
This post is riddled with facts about bats that I didn’t know before and that’s thanks to Heidi and the Wildlife Trusts. I could go on about them for a while…so try and stop me! Bats appeared on the scene around 80 million years ago! This means they survived the K/T extinction event 65MYA, which is famed for wiping out the dinosaurs! We all know that bats sleep upside down, but how do they manage it? When humans relax our hands they lay nearly flat and when we contract our muscles our hands grip; bats are the opposite. This means they can sleep soundly without the worry their grip will falter, because even when relaxed in deep sleep their grip will remain tightly locked in position. Bats are so darn cool!
When walking around the common we encountered ~5 individual bats and we think, owing to their frequencies, that they were three different species. On the edge of woodland and hedgerows we predictably found the UK’s smallest species (pipstrelles), over the pond a slightly larger Daubenton’s bat was swooping low and in the open areas a serotine was detected.
I would definitely recommend going on a bat walk with your local Wildlife Trusts, but be quick! They bats are going to be hankering down to hibernate in the next few months, so this is your last chance to see them in 2016! Click here to see what events are happening near you or go to your local Wildlife Trust website. Good luck, I hope you see some flying furries!
Animal Sam 