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Flying Creatures of the Night

Big Brown Bat (Eptesicus fuscus). Photo by Dan Riskin, used with permission.

Last year, in August, I had the privilege of going for my first ever night-time hike. The hike itself was extremely short and straightforward but the goal wasn’t distance or challenge. The goal was to see and hear some of the flying and screeching mammals that come out at night: Bats.

To see these creatures, you need to go out at twilight, which is what myself and members of the Norfolk Field Naturalists did in August 2022. The night sky was beautifully clear, and as stars began to appear so too did small flying creatures seeking insect prey with high-frequency calls. I think everyone knows that bats use echolocation to locate prey in the darkness, but something else everyone “knows” is that bats are blind… but this isn’t true at all. Bats can see about as well as we can, which is to say that they can’t see amazingly at night. To compensate for this, bats create extremely high-frequency calls that are beyond the range of human hearing, and interpret the reflections of these calls, discerning objects (ie. Flying insects) that break up the soundwaves they create before the soundwaves return to the bats’ extremely sensitive ears.

Despite what I said earlier about most of their echolocation calls being too high-frequency for human hearing, I was able to listen in on their hunting cries with the aid of technology, an amazing experience. I used a bat detector which works by bringing any frequency sound down 100 Hz so that high-frequency sounds are emitted within human hearing range. This meant a bit of fiddling with the dials to hit the right frequency that the bats were calling at. 

This is the Bat Detector that I borrowed and used for the evening to listen in on hunting bat calls.

Once I got the hang of it, I was able to listen in on bats hunting in the night. The input was directional, so I had to aim my detector at where I thought a bat was flying which became increasingly difficult as the sky darkened. This obscurity was rewarding when I would happen upon a bat that I could not see by just scanning the dark sky with the detector. There were a few side effects of detecting high-frequency sounds and transmitting them loudly to my headphones. One was that on a certain frequency I could hear very distinctly a loud jangling and clinking sound every time that a fellow Field Naturalist put their hand into their pocket and bumped their keys. Another was that if I tuned into another frequency, the already-audible calls of many katydids in the woods became deafeningly loud in my ears. Whenever I caught the bats’ channel of calling and honed in on a hunting bat, any drawbacks were instantly alleviated.

Which kinds of bats were we observing? According to the website batnames.org (an online taxonomic tool tracking bat diversity) there are 1456 bat species named worldwide (Simmons and Ciranello 2022). Within Mammals, the order Chiroptera is second only in species diversity to the incredibly diverse order Rodentia (with approximately 2635 named species (Mammal Diversity Database)). Within Canada, there are just 20 species of bats, all belonging to the Family Vespertillionidae (Naughton 2012). Within Ontario, there are only 8 species of bats*, so we really only have the tip of a very massive iceberg of bat diversity worldwide. Our hike was led by Liv Monck-Webb of Nature Conservancy Canada and she identified the bats we heard and saw as likely belonging to just 2 species: Big Brown Bats (Eptesicus fuscus) and Eastern Red Bats (Lasiurus borealis).

*Big Brown Bat (Eptesicus fuscus), Silver-haired Bat (Lasionycteris noctivagans), Eastern Red Bat (Lasiurus borealis), Hoary Bat (Lasiurus cinereus), Eastern Small-footed Myotis (Myotis leibii), Little Brown Myotis (Myotis lucifugus), Northern Myotis (Myotis septentrionalis), and Eastern Pipistrelle (Pipistrellus subflavus) are the regularly occurring 8 species of bats in Ontario. Apparently there has been a single specimen of the Evening Bat (Nycticeius humeralis) found in Ontario on Point Pelee in 1911 (Naughton 2012). Naughton (2012) goes on to say that this species could appear more frequently in Ontario in the future with warmer average temperatures.

I would like to talk about the two bat species we observed in more detail in future blogposts, so stay tuned for that!

Eastern Red Bat (Lasiurus borealis), photo by NACairns, used with permission.

Being able to listen in on bats hunting was an incredible experience, and unlocked one more piece of local ecology. If you have the opportunity to do the same, I would highly recommend it!

References:

Simmons, N.B. and A.L. Cirranello. 2022B. Bat Species of the World: A taxonomic and geographic database. Accessed on 12/29/2022.

Mammal Diversity Database. (2022). Mammal Diversity Database (Version 1.10) [Data set]. Zenodo. https://doi.org/10.5281/zenodo.7394529

Naughton, Donna. 2012. The Natural History of Canadian Mammals. University of Toronto Press.