NIGHTS OF THE SPRING PEEPERS

Spring Peeper, Pseudacris crucifer, male peeping during spring mating season

Spring is nature’s most joyous time to be a naturalist in northern latitudes as the world awakens from its long winter sleep. Near our Michigan home, Amish farmers are out in early March, when they begin to collect Sugar Maple sap from the awakening trees, and they use horse-drawn plows to prepare the earth for planting. Wave after wave of birds arrive from the southland, from Sandhill Cranes to Baltimore Orioles and hundreds more. The land awakens with spring wildflowers before the trees leaf out. The first insects appear, including Mourning Cloak butterflies that have overwintered under bark or leaves, and the Common Green Darner that has migrated up from the south. These are all great stories for a naturalist, but there is also a chorus that, to me, signifies that spring is here.

Video of Spring Peeper calling next to the pond

When night time air temperature rises into the range of about 35 to 40 degrees Fahrenheit, each little pool in the forest comes alive with the songs of Northern Spring Peepers. These tiny chorus frogs, each about the size of a thumbnail, peep together around the shores of a permanent or temporary pond–one that has no fish as predators. These are all male frogs trying fervently to attract mates. The calls begin shortly after sunset and end in the early morning hours, before the first traces of dawn light bring predators in the form of birds to the ponds.

Where I live in the middle of Michigan’s mitten, there are numerous little glacial kettle ponds, left as chunks of ice by the last ice age. When the ice melted, it left a depression filled with water, with high banks surrounding the new pond. These ponds are too small to support fish but are just right for Midland Painted Turtles, Common Eastern Toads, and Northern Spring Peepers. I set out on two nights to figure out how to see and photograph the peepers and I chose a pond that I could have easy access to. On the first night, the peepers were calling loudly when my nephew and I slip-slided down the steep hill leading down to the kettle lake. The frogs heard us coming and immediately became deathly quiet. We patiently waited without moving, and the peeps gradually slipped from stealth mode and awakened the heavens again with joyous noise. I spent a long time looking for the source of the calls, and finally found one little peeper calling from under the overhang of a fallen oak leaf right next to the pond. I was only able to get one photograph with a macro lens, a large bulky lens next to these tiny creatures. It was the opposite of stealth.

The setting: a small glacial kettle pond in the forest

Two nights later, I returned to the same pond, this time with my wife, Karen, and with the plan of using a snout wide-angle macro lens, which is about 18” long and only 5/8” in diameter at the lens end, which meant my face could be farther away from the peepers and I could approach them with stealth and cunning, or at least my version of stealth and cunning, which is usually clumsy and loud. 

We were quieter in approaching the pond than on my previous expedition, so the peeps barely interrupted their chorus of desire upon our approach, despite our use of bright flashlights. I showed Karen where I expected to see the frogs based upon my previous night’s work, but that proved to be fruitless, or frogless. In searching around a patch of shoreline where a peeper was loudly calling, we just couldn’t find it on the forest floor. But then I happened to see movement about 18” off the ground, and it was a Spring Peeper calling while clinging to the dry stalk of a wild perennial left over from last fall. Its little vocal sac was expanding with each call–so incredibly exciting to see in real life!

Spring Peeper male calling using air sac at throat [photo shows how sac expands]

Spring Peeper male vocalizing from its perch on an oak leaf

So I set up my snout lens on a tripod and approached to within about an inch of the calling frog. Meanwhile, Karen used a dive light–a powerful LED flashlight meant for deep dives in the ocean–to light the frog. Somehow, it didn’t mind the light too much and I was able to get hundreds of close-up photographs and videos of this frog and two of its nearby rivals in some of the most exciting hours I’ve ever spent (and, yes, I am truly a boring person). If you ever have the chance to experience the sounds of Spring Peepers while standing among them, don’t miss the opportunity!

MORE DETAILS ABOUT THE LIVES OF SPRING PEEPERS 

The Spring Peepers calling in a chorus around a pond are all males, trying desperately to attract mates. Presumably the biggest and loudest male wins the wooing contest, allowing them to mate with the quiet and choosy females. After mating, the female lays eggs in the little pond. Tadpoles are the hoped-for result, and the cycle of life continues.

Spring Peepers are the color of leaf litter on the forest floor: tan or brown or green. Hence they can remain disguised. The second word of their scientific name, Pseudacris crucifer, refers to the large dark cross on the back of each frog. I believe this is part of the camouflage, which breaks up the otherwise uniform color and looks like the veins of a leaf.

A Spring Peeper looks a bit like a dried leaf on the forest floor; the cross marking on the back and other markings on the legs break up the color, making it look more like fallen leaves

These are tiny creatures. In fact, were you so inclined, you could mail seven of them in a one ounce first-class mail envelope, though the USPS and peeps wouldn’t be very happy.

Spring Peepers are tiny in comparison with the loudness of their group

Peepers go into suspended animation all winter, spending the long, cold months hiding behind a flap of bark on a tree or under a fallen log or under the leaf litter on the ground. Their bodies can survive freezing down to about a 17 degree Fahrenheit body temperature because of glucose and other chemicals in the blood that act as antifreeze.

To get these pictures, I used a long Laowa Macro Probe lens with a strong dive light

To make their calls, the males take air into their lungs, then close off their nostrils and mouths. As air is forced from the lungs by muscles, it passes over vocal cords and into the inflated air sac, creating the sound variously described as peeping, chirping, or sleigh bells. The sound is loud enough to prevent sleeping for some people, and is a shimmering shower of sound when it surrounds us next to a pond.

The slightly bulbous toe pads are designed to stick to wet or dry vegetation to facilitate climbing

Just to the right of this calling Peeper is the warty leg of a much larger Eastern American Toad

A typical male peeper can make up to 13,500 calls per night, though I didn’t do the math and am depending upon scientists for this factoid.

And the most astounding fact of all: a group of Spring Peepers around a pond is referred to an an “army.” A noisy and tiny army, but an army nonetheless.

Video of the calling Spring Peeper right next to the Toad

The photographs below include other inhabitants of this pond: an Eastern American Toad showing off the gold flecks in his eye; Midland Painted Turtles basking on logs; a few more Spring Peepers; and a view of tree reflections on part of the pond. Click on each to make it larger.

GLOWING PINK FLYING SQUIRRELS: Biofluorescence Revealed

Southern Flying Squirrels, Glaucomys volans, glowing hot pink on their underbellies when illuminated by a 365 nm UV flashlight, in a rare phenomenon known as biofluroescence

I awoke last night at midnight to flashes of light from a motion sensor floodlight on our deck. I wasn’t thinking of prowlers, because I suspected the flashes of light were triggered by Southern Flying Squirrels coming to visit for the sunflower seeds I had tossed out just before going to bed.

I crept downstairs and carefully opened the sliding door, letting in frigid February air. The deck light came on briefly, enough that I could see the tiny squirrels dashing up through an opening in the deck around a huge Northern Red Oak. Each squirrel would come up, grab a sunflower seed, then dash down the tree trunk out of sight. This happened so fast that I couldn’t see how many squirrels there were, though at one point I saw three. There may have been more. On this night they were nervous and did not stop long enough for any photos.

We’ve had Southern Flying Squirrels at our home in Michigan each winter, and I’ve photographed them at night several times using incandescent lights on the deck. They made for good photographs, with their gray-brown fur and a cuteness factor of huge bulging eyes and little pink lips, but their coloration was subtle to my eyes and essentially no different from most mammals, which are colored for camouflage rather than display.

Then scientific knowledge suddenly changed. About four years ago a Wisconsin forestry professor, Dr. Jonathan Martin at Northland College, was in the woods at night looking up toward the forest canopy with an ultraviolet flashlight for lichens and other fluorescing lifeforms, when a hot pink missile glided overhead. He identified this as a Northern Flying Squirrel, and its normally white belly lit up hot pink in ultraviolet light. He found this astounding, and asked a colleague to investigate flying squirrel skins in a couple of museum collections to see if the phenomenon could be confirmed. It turned out that in those collections, the bellies of all three species of North American flying squirrels–Southern, Northern, and Humboldt’s Flying Squirrels–glowed bright pink under UV light. Even specimens over 100 years old. Male and female, young and old, they nearly all glowed.

Since we have easy access to flying squirrels at our home in Central Michigan, I decided to observe this phenomenon for myself. I obtained a 365 nm UV flashlight that is powerful enough to look almost into the treetops and began looking at these squirrels on nights they chose to come to our feeding station. They don’t come every night, but when they do I often get up in the middle of the night to observe and try to photograph them. It isn’t easy to photograph little nervous squirrels by a relatively dim (to our eyes) UV light, but I’ve had some success represented by the pictures here.

Southern Flying Squirrel showing biofluorescence under UV light on the left, with the same species illuminated by tungsten light on the right. The belly fur changes from off-white to bubblegum pink when struck by UV light.

Why do flying squirrels glow? That is still unknown. What is known is that at dusk, dark, and dawn, the air is bathed in proportionately more ultraviolet light and far less light from the visible spectrum than in daytime. This UV light–when converted to visible light by fluorescence–makes the flying squirrels more visible to each other. This is even more true when snow blankets the forest, since snow reflects UV light. It also appears that flying squirrels’ eyes, unlike ours, can see into the UV spectrum, so this ability may also be involved.

Again: why do they use biofluorescence and UV light at night? There are a couple of possibilities that spring to mind. Based upon the three flying squirrels I observed on that recent February night, I think it’s possible that the squirrels use their bubblegum pink undersides to keep track of each other at night. These squirrels are highly social, with reports of 25 to 50 Southern Flying Squirrels roosting communally in a hollow tree. So why wouldn’t they follow each other to food sources? Some of my pictures show them sitting side by side, dining quietly together on the sunflower seeds I put out. They seem to enjoy a more peaceable kingdom among their kind than do the daytime Eastern Gray Squirrels and American Red Squirrels we also get in Central Michigan. Feeding together also means more big eyes to look for predators–much as goldfinches and other songbirds feed communally as a strategy to detect hawks.

There is another tantalizing possibility for the pink color. Three large owls that also live in this region–Barred, Barn, and Great Horned Owls–also have bellies that fluoresce hot pink under UV light, though their coverings are feathers rather than fur. These owls are the chief predators of flying squirrels. Do the flying squirrels mimic the owls to fool the predacious birds into thinking they are seeing other owls when in the air? Maybe. I find this possible. The fluorescing fur is mostly on the belly and undertail of the squirrels, with just a minor hint of color change on the back and virtually none on the tail. Once a flying squirrel lands on a tree trunk, its back and tail make it almost invisible to predators because the glowing belly is nearly hidden.

Alternatively, perhaps the owls are mimicking the flying squirrels, fooling the little squirrels into thinking they are seeing others of their own kind. This would allow the owls to silently approach the flying squirrels and suddenly grab the little creatures.

Or perhaps all three of these mechanisms are in play: bubblegum pink signals the presence of flying squirrels to each other, but also both disguises them from owls and identifies them to owls, if any of that makes sense. Coevolution at work.

Biofluorescence also extends to the Virginia Opossum in this region, but is apparently unknown in other mammals here. It turns out the phenomenon is new enough that the chemical and physical mechanism is still unknown. I suspect this will be studied in coming years, with possible applications for industry. Or not. Knowledge is its own reward.

I will be watching these creatures over the coming weeks and years, both with and without the assistance of UV light. The mysteries of nature are an ingrained part of my life and I find observations and photography endlessly fascinating.

The photographs above are a good representation of the Southern Flying Squirrel in UV vs visible light. The final photograph shows the deck setting at night where all the pictures were taken, and includes one flying squirrel for scale. Click on the photographs to see them larger.

Here are some other sources that examine this discovery:

Ultraviolet fluorescence discovered in New World flying squirrels (Glaucomys) (Journal of Mammalogy)

Southern Flying Squirrel (Wikipedia)

Flying Squirrels Glow Fluorescent Pink Under Ultraviolet Light (Smithsonian)