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Bat Series – Here comes the night

As halloween approaches, batty decorations make an appearance in shops and homes. But how much do we know about the world’s only mammal capable of true flight? 

Not a fan of spiders? – Bats eat those!

There are 17 or 18 resident species of bat in the UK (depending on who you ask…I’m not getting involved with that debate) and they are all nocturnal and insectivorous. This means they all come out after sunset (spooky) and eat insects. I was once told by someone that a bat flew into their hair. This is a weirdly common complaint from people about bats but also very unlikely. The common phrase ‘Blind as a Bat’ is highly inaccurate. In fact, bats have very good eyesight, probably just as good as humans, the only problem is that they forage at night and humans would struggle too if we had to find our food in the dark! To be able to find food in the nighttime bats use echolocation (also called sonar) and to avoid flying into trees, buildings, or other bats. The echolocation abilities of bats are so good that some species of bat, known as gleaning bats, can pick a spider off its web (in the dark!), having ascertained which side of the web the spider is on, all while ensuring that the bat’s wings don’t get tangled in the web. Not all bats are gleaners, some species hunt whilst in flight, or on the wing, and are known as aerial hawking bats. And finally, some bats, such as the Daubenton’s bat, are known as trawlers because they use their tails to hunt insects from the surface of water.

When surveying bat, you may record snippets of sonar to produce sonograms like the one above. This sonogram is showing a bat of the Myotis genus.

Don’t like midges and mosquitoes? – Bats eat those too!

Bats roost in cavities or crevices of trees or human-made structures. They do not build roosts so will use structures already in place, such as holes in trees made by woodpeckers, or crevices formed from ivy growing up a tree. There are a number of different types of roost which bats form at different times of year. Over winter, bats form hibernation roosts. Bats hibernate over winter as there is not enough food to sustain them over the cold period, which lowers their metabolism so they can conserve enough energy to take them into the spring. When spring comes and the weather warms, bats begin to emerge from their hibernation roosts for longer and longer stretches of consecutive nights. Come summer, bats are ready to reproduce and female bats will form maternity roosts in which they will gather to give birth to and raise their young. The bats give birth whilst hanging. They turn themselves around so they are hanging from their wings, instead of their toes, and give birth into their tail. The young bat, or pup, then climbs up the mother’s fur and clings on while she returns to her upside down hanging position. The pups spend 4-5 weeks clinging onto their mothers before being able to fly alone. The maternity colonies break up later in the summer. It is vital that maternity colonies are not distrubed, due to the potential of the mothers abandoning their pups if they are.

Bats are the only mammal capable of true flight because flying squirrels don’t count!

Whilst all bats species are protected within the UK, some species are more vulnerable than others to the built environment and land use change. Larger bats, including Myotis species, tend to be more sensitive to the effects of human society, including light pollution and deforestation, due to their size and wing aspect ratio. This is particularly true of Myotis bechsteinii (Bechstein’s Bat) which is a ‘narrow space’ forager1 and a light sensitive species, like many Myotis species. Deforestation has a significant effect on these bats which have evolved to forage in narrow space environments, because they are not as equipped to forage in open space and can be out-competed by other bat species, such as Pipistrelle species, which are better suited for these open environments. Moreover, many bats will not roost in buildings, instead taking a preference of roosting in trees. Deforestation and the removal of ancient woodlands removes a vital place of rest for these bats. Saplings do not make for appropriate roosting places and therefore cannot be expected to replace ancient woodland as habitat. Without places to rest and forage, bats would face increasing difficulty in being able to sustain populations and could drive already vulnerable species further towards extinction. 

To find out more about bats, their roosts, and why they are important, head over to the Bat Conservation Trust website where you can find out a wealth of information about all things bats.


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