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Nocturnal Frequencies


By Stephanie Kozak, Interpreter 

Whether overlooking a prairie, kayaking on a lake, or taking a stroll on one of our nature trails, there is not a sight more warm and inviting than a sunset in the Metroparks.  Sunsets allow us to pause and appreciate nature for a lasting moment.  But, after that moment has passed, we usually take it as a cue to pack up and head out.  Yet, here at the Metroparks we are still open after the sun has gone down—until 10 p.m., in fact.  If you are one of the brave few willing to stick around a magical world awakens as the sun goes down.  In Kensington Metropark our Sandhill Cranes, Great Blue Herons, Eastern Chipmunks, songbirds, and squirrels settle into their homes for the night, but nocturnal creatures start to emerge.  Come take an imaginative hike with me as we explore one of the nighttime creatures of Kensington, the bat.

Currently, it is the common human habit to pull out your trusty flashlight when it begins to get dark, but I urge you to go against your habits and keep that flashlight hidden.  Head northeast out of the Kensington Nature Center and away from the building lights down Deer Run Trail.  About 200 yards down the trail stop at the first boardwalk before trail marker 16.  At twilight, about fifteen to twenty minutes after sunset, pause at this open sky area close to the trees and water and look up.  Allow your eyes to adjust to the dark to better see the animals that emerge.  What you see flying in between the trees above the water in front of you is not a bird, it is actually a bat.  Scientifically known as Chiroptera, or “hand-wing”, bats are the only true flying mammal.  Thin layers of skin stretch between extremely long fingers, making up the wing of the bat.  This unique skeleton makes for an interesting flight pattern.  Bats are manic when they fly overhead. They don’t fly from tree to tree, or stop and rest like a bird.  They fly up and down, left and right, in frenetic patterns.  From the second they come out of their roost, where they spend the day sleeping, they are airborne looking for insects to eat.  They hunt until they are full and return to their roost to sleep the next day away.

As you watch the bats flying around you may wonder how they can maneuver through the air so quickly catching insects.  A common human myth is that bats are blind, but they can see just as well as we can in the dark.  Needless to say, we wouldn’t be able to fly that fast through the sky without running in to something, let alone catching an insect.  Bats use sound to navigate, a technique scientist have named echolocation.  A bat makes a noise with its throat, tongue, or through its nose.  This creates sound waves that travel towards an object like a tree or insect. The bat waits for the sound waves to bounce off the object back towards them.  Based on the speed and frequency that the sound waves bounce back with, the bat can tell if they are flying towards an insect that they want to eat or a tree they need to avoid.  The bats make a noise, the noise echoes back to them and they locate where the prey is in relation to them, hence the name echolocation.  Studies have proven that bat echolocation is so exact that they can detect a single strand of human hair in complete darkness.  While you are out there observing the bats you won’t be able to hear their echolocation patterns. Sometimes you can hear a tongue click here or there, but the frequency that the bats use to echolocate is too high of a frequency for human hearing.  Bats echolocate at a frequency between 20 to 200 kilohertz.  Luckily, humans can hear, at a maximum, frequencies 20 kilohertz or less.  I say luckily because one of the most common bat species in Michigan, the little brown bat, echolocates at such an intense decibel that it could be damaging to your hearing.  If we could hear that sound it would be like holding our ear 10 cm away from a currently ringing fire alarm.  I don’t think any of us would enjoy that.

At around 9:45 pm the darkness truly sets in, providing cover for our amazing night time animals: flying squirrels, owls, coyotes, raccoons and opossums.  At this time the bats are too difficult to see with the naked human eye as they swoop by, blending in with the backdrop of the night sky.  As you walk to your car and drive out of the park listen carefully to the nocturnal frequencies that our human ears are able to hear like the Gray Tree Frogs, crickets, owls, and the distant coyote’s howl.

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