Bats

Above, Greater and Lesser Horseshoe Bats. All of the illustrations of bats are from Thorburn (Archibald).  British Mammals.  Two volumes.  Longmans, Green & Co., 1920-1921.

This, however, I took many years ago during a trip to India. It’s the Neemach Mata Temple overlooking Udaipur and Fateh Sagar Lake. As the sun set over the city, a quiet murmur grew to a hubbub of conversations carried by the gentle wind and we watched as the lights came on and twinkled. Suddenly, from the mouth of a cave we had not even noticed, hundreds, more likely thousands of bats streamed out in one of the most incredible natural displays I have seen in my life.

We were also lucky to see these Egyptian Vultures. This is the Indian sub-species Neophron percnopterus ginginianus.

Just before Halloween, a night that does the reputation of bats more harm than good, the Binfield Badger Group was treated to a talk about bats by Emma Turnbull from the Berkshire and South Buckinghamshire Bat Group.

Barbastelle and Long-eared Bats

We are blessed with eighteen species in the UK, all but one of which breed here. This list, from bats.org.uk, shows that some imagination has been put into their naming.

• Common pipistrelle
• Soprano pipistrelle
• Nathusius’ pipistrelle
• Brown long‑eared bat
• Grey long‑eared bat
• Greater horseshoe bat
• Lesser horseshoe bat
• Alcathoe bat
• Daubenton’s bat
• Barbastelle bat
• Bechstein’s bat
• Brandt’s bat
• Leisler’s bat
• Natterer’s bat
• Noctule
• Whiskered bat
• Serotine bat
• Greater mouse‑eared bat

Noctule and Pipistrelle

I am as sure as I can be that it is Noctules who visit the garden on summer evenings.

Bats are the only (powered) flying mammals – pretenders, like the Flying Squirrel, in fact just glide.

The oldest fossil we have found is from 52 million years ago and they have changed little in all that time. Their bones are fragile and so not many fossils are discovered.

There are mega bats, the fruit bats, which can weigh up to two kg and can boast a two metre wingspan. And there are micro bats, the smallest no larger than a bumblebee. We know of some 1,500 species and are still learning of more members of the Chiroptera (‘Flying hands’) family. The skeletal wing structure is not so different from that of human arms, hands and fingers. Bird bones are hollow, bats are thin instead to cut down on weight. Their tail membranes act like a rudder and their heart rate can vary from 20 to 1,300 beats per minute depending on what they are up to.

Serotine and Leisler’s Bats

They are largely insectivorous although some eat spiders too and incredibly, they make up one third of all our mammal species. Since there are no insects to catch in the winter months, whilst they don’t fully hibernate they do go into a state of torpor. Pipistrelles can eat more than 3,000 midges in one night. Noctules go for large beetles, cockchafers and moths, Long-eared bats specialise in moths and have developed their ears (rather than relying on echolocation) so that the moths can’t hear them coming.

They lose a lot of moisture through their membranes and so they need it in their environment, favouring trees, churches, bridges, caves, tunnels and especially cavity walls. During maternity they require hot places. They mate at swarming sites in the autumn and the females store the sperm until spring – insects appear when temperature is at at least eight degrees – and they have just one pup per year, born at between 20 and 30% of the mother’s size, suckling for six to eight weeks. They are of course terribly vulnerable in the roost – but they can fly after only three weeks, although it takes them a while to acquire the requisite skills to do so proficiently.

Pipistrelles are our smallest species, 4-7 kg and with a 18-24 cm wingspan and exhibit an erratic, bouncing flight just above human head height. We only learnt that were two sub-species in the 1990s, the Soprano and the Common. The former are loud and roost in large numbers.

Noctule wingspan is between 32 and 45 cm, they fly high and fast in straight lines and have very loud calls. Daubenton’s, wingspan 23 to 27 cm, are also known as Water Bats and, having large hairy feet, take insects from the water surface, whilst Brown Long-eared or Whispering Bats (24 to 28 cm) are very quiet and use stealth to catch their prey.

Daubenton’s and Natterer’s Bats

Echolocation calls vary in rates and frequencies and the rate is linked to the beats of their wings. Bat detectors are far from completely reliable and automatic identification is even less so. They are highly loyal to their roosts.

Pipistrelles generally live for between ten and fifteen years, others may last for 35 or even 40.

Wind turbines are a real problem for them. Deaths are mostly not from impact with the blades but the dramatic changes in barometric pressure which cause barotrauma, rapid lung expansion and internal haemorrhaging. The partial solution is to turn the turbines off at peak migratory times.

There are of course ‘vampire’ bats but only in South and Central America and there are only three species. The anticoagulant draculin in their saliva and synthetic versions of it are proving useful in human medicine.

This was an excellent talk. Emma slightly underestimated her audience when it came to myth-busting. We are a pretty wildlife savvy group and so no one thought bats got tangled in our hair or any other nonsense, nor did we doubt their importance as controllers of ‘pests’, pollinators and dispersers of seeds. It was also clear, however, that there is a vast amount that we humans still do not know about this amazing species. I will be installing a bat box or two – we need to do all we can to protect them.

Bechstein’s and Whiskered Bats