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Bats in the Dunes

Dynamic Dunescapes

Though not given quite the same press as bumblebees or butterflies, our native bat species are an important part of so many of the United Kingdom’s ecosystems – they even make good use, it turns out, of our sand dunes.

The UK is home to 17 breeding species of bat (all of which are legally protected), so these winged, nocturnal creatures make up nearly a quarter of our mammal species. Of course, we play the role of gracious AirBnB host to a few other visiting species at times, too.

Around the world, some of the 1,400 species of bats are adapted to feast out on fruit, nectar and larger prey like frogs and other bats. But that’s not the case in the UK, where all of the bat species you’ll find live exclusively on a diet of insects. [1] In fact, these efficient predators are actually pretty useful when it comes to keeping certain insect populations in check, particularly when some invertebrate outbreaks threaten agricultural land or forests. [2]

Despite staring as spectral characters in folk tales and having their likeness adorn decorative items to celebrate Halloween, bats, in an ecological sense, are symbols of good news. They’re sensitive to changes in their environment and are often used as indicator species; a healthy food chain and happy habitat will support populations of bats, but when issues arise like pesticide, light or noise pollution, bats are among the first to go. The absence of bats, in fact, is far more foreboding than the presence.

Brown long-eared bat. Photo by Nils Bouillard on Unsplash
Photo by Nils Bouillard on Unsplash

Bat numbers in the UK have declined over recent decades and understanding their population sizes and changes is vital when working out how to support them. [3] However, their daily routine – sleeping in sheltered nooks during the day and emerging at dusk to feed – can make bats tricky creatures to try to see, certainly in any detail beyond shadows flitting through the sky as the sun sets. So, for ecologists to survey bats or for wildlife fans keen to see if, and what, bat species might reside nearby, vision alone cannot be relied on. Instead, we have to turn our attention to sound.

Many bat species, including all of those found in the UK, use echolocation to navigate and hunt in the dark. By contracting their larynx (voice box) they produce ultrasound soundwaves. These bounce off objects nearby and are picked up by specialist receptor cells in bats’ inner ears, allowing them to accurately ‘see’ the environment around them acoustically. [4] We can’t hear these sound waves, as they’re in a frequency too high for humans, but we can use bat detection devices which contain an ultrasonic microphone to tune into these soundwaves.

Different species of bat echolocate at different frequencies, so we can also tune bat detector devices to known frequencies to see if a certain species is nearby, or we can scan through all of the frequencies until we find echolocation. We can then use its frequency, as well as the call pattern and things like the flight pattern and the size of the bat (if we can see them) to help identify the species.

Nathusius's Pipistrelle. Photo by  Nils Bouillard on Unsplash.
Nathusius's Pipistrelle

According to stereotype, bats reside in caves and run-down buildings, while age-old legend and lore report that they cross into the underworld and associate with vampire high society. While the first is partly true (some species do indeed relish shelter provided by old buildings) and the second is up for debate (on October 31st, at least), many of us will know that woodlands are an important roosting site for bats and that they can often be seen hunting around water. The air above ponds, rivers and streams on a warm summers’ eve is often filled with dancing insects, and so too with the darting shadows of hunting bats.

One thing that is rarely included in bat pop culture is that, as we’re starting to learn, and sand dune systems can also offer them bountiful feeding grounds.

Sand dune grasslands, when healthy, support an abundance of native insect life including species that can be found in the air at dusk and through the night – particularly handy, when you’re a hungry bat. During the summer months moths, mayflies, midges and mosquitos are all on the moonlit all-you-can-eat menu.

On the Sefton coast, common pipistrelle (Pipistrellus pipistrellus), noctule bat (Nyctalus noctule) and brown long-eared bat (Plecotus auritus) have been recorded using some of the bat boxes installed at Ainsdale National Nature Reserve. A 2019-20 survey, saw five bat species using the NNR’s large dune system and, excitingly, even also identified Daubenton’s bat (Myotis daubentoniid) spending time in the open dune grasslands, away from the predicted dune ponds and woodland areas. Generally, greater bat activity across a range of species was identified in frontal dunes and open spaces, as opposed to habitat that contained scrub or woodland. [5]

It’s thought that bats will travel several kilometres from their roosts and use woodland that lines the far edges of dune systems as a commuting route, offering sheltered spots to rest, as they travel to the dune system for their evening meals. But, when the time comes to gorge, they stray away from the areas of dune where woodland has encroached.

Dynamic Dunescapes’ work to restore dune systems as rolling, open spaces with more bare sand that rubs shoulders with low grassland, and less scrub encroachment, could therefore benefit coastal bat populations. The creation of dune meadows by removing scrub bolsters insect richness, and so too do the restoration of dune slack pools – damp areas and ponds that sit between the dune ridges – to provide amphibian but also insect breeding habitat. Time (and more surveys) will hopefully tell a positive story for our enchanting and important nocturnal predators.

 

[1] Bat Conservation Trust https://www.bats.org.uk/

[2] Riccucci, M & Benedetto, L (2018) https://www.researchgate.net/publication/328133405_Bats_and_insect_pest_control_a_review

[3] Wildfowl and Wetlands Trust https://www.wwt.org.uk/discover-wetlands/wetland-wildlife/bats/#:~:text=Bat%20numbers%20have%20fallen%20dramatically,70%25%20between%201978%20and%201993

[4] Scientific American https://www.scientificamerican.com/article/how-do-bats-echolocate-an/

[5] British Islands Bats Volume Two, 2021 https://www.bats.org.uk/resources/accessing-journal-papers/british-islands-bats