Archives For Jim Steffen

While working out in the woods this winter, a small lump on the branch of a young elm tree caught my attention. At first I thought it might be a gall, or an injury that had healed-over. On closer inspection, the lump turned out to be a ruby-throated hummingbird nest from last summer. 

Although I see hummingbirds regularly at the Chicago Botanic Garden, I rarely encounter one of their nests. Hummingbirds themselves are amazing, but their nests are truly a marvel of avian architecture. Not much larger in diameter than a quarter, they are just large enough to hold the one to three navy bean-sized eggs of the hummer. For the pint-sized bird to be able to keep the tiny eggs warm during incubation requires that the nest be not much larger than her body. 

PHOTO: Hummingbird nest and quarter (for scale).

Not much larger than a quarter, the ruby-throated hummingbird nest is an engineering marvel.

This is all well and good until the eggs hatch. Growing young hummingbirds can double or triple the amount of room necessary to hold the family. One of the ways the hummingbirds get around this need for flexibility is that they construct the nest of soft plant fibers and then wrap the whole thing with spiderweb silk. This creates an elastic nest that has the ability to expand as the contents of the nest increases. Can you imagine yourself going out and plucking a strand of sticky silk from a spider web with your fingers and then trying to use it to build something out of lightweight fuzzy plant fibers? I imagine you might find yourself wrapped up in a ball like some sort of oversized grotesque moth cocoon. The silk also helps to anchor the nest to the top surface of a horizontal branch.

PHOTO: Spiderweb silk is used by hummingbirds as a nest liner.

Spiderweb silk: the expandable nest liner preferred by hummingbirds.

Keeping the nest just the right size as the need arises helps to keep the growing youngsters warm and secure. In the western states where several species of hummingbirds nest, often at higher elevations, it is not only important to keep the nestlings warm, but also the incubating female, especially at night. Therefore, it is often the case that hummingbirds in these colder situations will locate their nests on a limb with an overhanging branch acting as a sort of roof to help block the nest from the night sky. 

Although this measure helps reduce heat loss, it is often the case that nesting females will go into a state of torpor (reduced physiological activity to lower body temperature) in order to conserve energy on particularly cold nights. This is a principle of physics in which the larger the difference in temperature between objects, the faster the heat flows from the warmer one to the cooler one. Therefore, a hummingbird with a lower body temperature will lose heat more slowly than the one with a warmer body. As I stated earlier, hummingbirds are amazing!

PHOTO: Parmelia sulcata, a common lichen, is used to help disguise the hummingbird's nest.

Parmelia sulcata, a common lichen, is used to help disguise the hummingbird’s nest.

Part of the reason—besides size—I had not noticed the nest earlier is that the birds do a fantastic job of camouflaging it. This also relates to the spiderweb silk. Some or all of the silk used is sticky. Upon completion of nest construction, the birds collect bits of lichen and attach them to the sticky strands on the outside of the nest. Interestingly, the birds seem to always use the same species of lichen, one that goes by the name of Parmelia sulcata

Parmelia sulcata is a light greenish-gray lichen with a leafy (foliose) appearance. One of our more common lichens, it is often seen on the upper branches of trees, and was particularly abundant on the ash trees that died from emerald ash borer. I don’t know if the birds chose this species of lichen in particular or, being common, it is just found most often. It is also interesting that the birds seem to apply the lichens to the nest in an upright position, with the top facing outward, so they look like they could be growing on the nest.

Come birding at the Garden! Take a birding class; join a group, and check your finds against our bird list.

Although this process is fascinating, it is not restricted to hummingbirds. One of the other breeding birds at the Garden utilizes a very similar nest construction technique to hold its three to five small eggs. The blue-gray gnatcatcher, another tiny bird (that somewhat resembles a miniature catbird in appearance and sound), also constructs a nest out of soft plant fibers, including spiderwebs, and applies lichen to the outside of its nest. A nest of this species, a little larger than that of a hummingbird, was found on a branch of one of the locust trees growing in a Garden parking lot.

PHOTO: A female ruby-throated hummingbird (males have the ruby coloring) enjoys a sip of salvia nectar in Circle Garden in summer.

A female ruby-throated hummingbird (males have the ruby coloring) enjoys a sip of salvia nectar in Circle Garden in summer.

PHOTO: A blue-gray gnatcatcher at the Garden; females look similar, but are less blue.

A blue-gray gnatcatcher at the Garden; females look similar, but are less blue.

If you’re lucky, you might find the nest of one of these birds during the nesting season, but if not, keep an eye out for little bumps, lumps, and knobs on bare branches in winter. You might get lucky.

Come #birdthepreserves with the Forest Preserves of Cook County. View our list of upcoming events for free events near you.


©2016 Chicago Botanic Garden and my.chicagobotanic.org

If You Can’t Take the Heat, Stay Out of the Fire

Burning prairies wisely saves animal and invertebrate life, while regenerating the plant landscape.

Jim Steffen —  March 10, 2016 — 2 Comments

This winter has been unpredictable with unusually warm weather one day and biting cold the next. During one of those particularly cold periods in January, I took advantage of the solid ice to work on removing woody invasive plants from one of our isolated wetlands in the McDonald Woods.

We have several such wetlands, but this one is perhaps more interesting than the others, in that it is home to a population of broad-winged skippers (Poanes viator)—an uncommon butterfly that has only been found on six or fewer sites being monitored for butterflies in the Chicago region.

PHOTO: Broad-winged skipper (Poanes viator).

Broad-winged skipper (Poanes viator)

This small brown butterfly is dependent on lake sedge (Carex lacustris) as a larval food plant on our site. It has been found to feed on some other sedge and grass species elsewhere, but here, that is the only plant that its larvae feed on.

In the 26 years I have been managing the 100 acres of the McDonald Woods, this small quarter-acre wetland is the only spot this butterfly can be found. Although there are many patches of lake sedge found throughout the woodland, apparently this butterfly will not leave this small and sunny wetland to venture into the surrounding shade of the oak canopy to take advantage of the other sedge patches.

PHOTO: Lake sedge in winter.

Lake sedge in winter

As I was working among the dormant lake sedge stems—solidly anchored in the thick ice of the wetland—I decided to do a little investigating to see if I could find any clues to the whereabouts of this butterfly in winter. Some butterfly experts think this skipper overwinters as a developing larva, then later pupating before emerging as an adult in early July. However, it seems as though no one is quite sure where exactly the developing larvae would be found.

PHOTO: Broad-winged skipper larva.

Possible Dion skipper larva

As I was working in the wetland, I occasionally plucked a dried-up stem of lake sedge and peeled the leaves back, much as you would peel a banana. Although I did not find a broad-winged skipper larva, I did find the larva of a noctuid moth, what appears to be the larva of a Dion skipper (Euphyes dion), some various fly larvae, a couple tiny adult flies, hundreds of sac spiders (Clubiona maritima), some Linyphiid spiders, Gnaphosid spiders, and a few other spider genera. Although I am well aware that many invertebrates spend their dormant periods hidden away in stems, leaves, and roots of plants, I was amazed to see how much life was present in the dried stems above a solid block of ice.

This revelation got me thinking about my management activities, and in particular, the use of controlled burning. Much like prairies, oak woodlands are dependent on fire to prevent fire-intolerant woody plants from moving in and creating too much shade for the “sun loving” oak trees to reproduce themselves.  

Prairies and oak woodlands evolved primarily as a result of climate, and in particular, rainfall. As you travel eastward from the Rocky Mountains, you first encounter short grass prairie where the rainfall is lowest, then mixed-grass prairie where it is a little wetter, then tall grass prairie where it is still wetter, then oak woodlands and eventually, eastern deciduous forest, dominated primarily by fire-intolerant tree species (like maple and beech), where the rainfall is most abundant.

PHOTO: Euphyes dion by Charles T. and John R. Bryson, Bugwood.org.

Euphyes dion by Charles T. and John R. Bryson, Bugwood.org

These prairies and oak woodlands provided a readily burnable fuel for any fire that got started, whether as a result of intentionally set fires by Native Americans or random lightning strikes. It is not hard to picture the description of early settlers when they wrote about fires that burned for days and covered hundreds of thousands of acres. As the prairie fire approached oak woodlands, they did not go out but continued to burn through the flammable leaf litter and dry herbaceous plants covering the ground of these woodlands.

But historically, these were huge landscapes. Today we are dealing primarily with tiny fragments of the plant communities that once covered thousands—if not millions—of acres. Because the landscape has changed and these remnants are now so small, they no longer experience the landscape-scale fires in which some areas burned while others did not. Back then, when habitats were huge and animal populations were large and widespread, these fires helped to maintain rich and diverse habitats and animal populations for thousands of years. It is always impressive, even after a single fire, to see the abundance of native seedlings emerge from the burned understory and later, the increased flowering of mature plants. But we don’t always consider the unseen other life forms hidden among the dried leaves and stems. Therefore, as managers, it is important that we utilize fire in a thoughtful way to try to restore and maintain all the richness in what remain of these once extensive natural systems.

Getting back to my experience in the winter wetland, there is a tremendous amount of invertebrate life that is present in the dry and burnable plant material in these dormant plant communities. This is particularly important when the entire population of a single species, like the broad-winged skipper, is found in such a restricted space. Plants and animals found in prairies and oak woodlands have evolved adaptations to periodic fires.

PHOTO: The Dixon Prairie in full bloom.

The Dixon Prairie in full bloom

Research has shown that most invertebrates are able to rebound after fire, but as managers, it is important that we make an effort to give these species the best opportunity to flourish on our small remnants. We can best do this by scheduling our burns—not burning the entire patch of any one particular habitat at any one time, especially during extreme weather conditions. And we should always try to leave some remnant vegetation unburned so that populations can regenerate themselves from those individuals that remain. Fire is an extremely important management tool for restoring and maintaining these natural communities, but it must be used wisely.


Photos @ Jim Steffen except where noted.
©2016 Chicago Botanic Garden and my.chicagobotanic.org

One of the most recognized lines from Shakespeare is the following: “Something is rotten in the state of Denmark.” You would have to read Hamlet to get the backstory, but one thing I know as an ecologist, is that we would be in a lot of trouble if there wasn’t a whole lot of rot going on all over the place.

You can probably imagine when walking through our oak woodland, that if things were not constantly rotting, you would be up to your eyeballs in dead leaves, and it would be almost impossible to walk anyway, because of the mass of dead branches and logs lying all over like a bunch of pick-up sticks.

PHOTO: Trichaptum biforme (a hardwood decomposer).

Trichaptum biforme is a hardwood decomposer.

Although there are a tremendous number of organisms that are involved in the rotting process, fungi are the very most important component of this team of decomposers. A tremendous number of species of fungi live in the McDonald Woods at the Chicago Botanic Garden; they can be broken up into two basic categories: those that form symbiotic relationships with living plants (mycorrhizal), and those that decompose organic matter (a.k.a. the rotters).

PHOTO: Another Trichaptum biforme (Violet-toothed polypore).

Another Trichaptum biforme (violet-toothed polypore)

While walking through the woods the other day, I tripped over a downed log and came face-to-face with one member of those decomposers, the bracket fungi. These familiar fungi, also known as shelf fungi, have a characteristic growth form. Most do not produce a stalk (stipe) that supports their cap. Instead, whether on a standing tree or on a log lying on the ground, the cap is attached directly to the wood and projects out horizontally like a shelf or awning.

Gravity causes tropism (the turning or bending in plants and fungi toward or away from an external stimuli), which causes the shelves to orient horizontally out from the wood. This is interesting to observe, especially when a standing dead tree that has shelf fungi falls to the ground, and the new fungi orient in a different direction after the tree falls. (This is one way that you can discover if a tree was dead before it fell to the ground.)

PHOTO: The beautiful layers of Trametes versicolor, or turkey tail fungus.

The beautiful layers of Trametes versicolor, or turkey tail fungus

Just like most of the “mushrooms” we find growing on the ground, these shelf fungi are the fruiting bodies of an organism that we seldom see. The actual organism is a spiderweb-like structure that is either sprawled out within the soil or, in the case of the decomposers, spread throughout the dead plant material.

What is important about these decomposer fungi is that they are able to breakdown cellulose and lignin—the building blocks of plants, and two materials that are unable to be decomposed by almost any other organism. Therefore, without the help of these fungi, we would be swimming in a sea of dead plant material, and all those nutrients and minerals would be locked up—unavailable for other plants to use.

Many of the shelf fungi differ from other fungi, not only because of their growth form, but also because they are usually very woody or leathery in nature. ( I can imagine that people mistake some of these fungi for a deformity in the tree when they feel them and realize that they are as hard as a rock. This is not true of all shelf fungi; some are soft and squishy and quite fragile.)

Some common shelf fungi are the artist’s conk (Ganoderma applanatum), the horse hoof fungi (Fomes fomentarius), the turkey tail fungi (Trametes versicolor), and the sulphur polypore (Laetiporus sulphureus).

PHOTO: Ganoderma species fungus.

Ganoderma species fungus

PHOTO: Sulphur polypore, or chicken-of-the-woods fungus (Laetiporus sulphureus).

Sulphur polypore, or chicken of the woods fungus (Laetiporus sulphureus)

The type of decomposition that takes place is referred to as either white rot or brown rot. In white rot, the fungi breaks down the lignin and leaves the cellulose behind. Wood that is being decomposed by white rot fungi turns off white and stringy. In brown rot, the fungi decompose the cellulose and leave the lignin behind. Brown rot fungi turn the wood reddish-brown and crumbly. In combination, the two types of decomposers reduce even large tree trunks to their component nutrients and minerals and make them available to the environment for living plants to use.

PHOTO: Stereum ostrea, or false turkey tail fungus.

Stereum ostrea, or false turkey tail fungus

Although some of the shelf fungi are interesting and quite attractive, like the turkey tail and violet tooth fungi (Trichaptum biforme), it is not a good sign to see them growing on your favorite shade tree. Some of these shelf fungi can be found on living trees where disease or damage has caused the decomposition process to begin, and may not portend a bright future for the tree. You might also see some of the fungi sprouting from structural elements of your home if the wood is unprotected and exposed to excess moisture—another sign of trouble.

Some of the shelf fungi are very prolific and can occur in the hundreds on a single log, or they might be one giant shelf that can be more than a few feet across and weight 50 to 100 pounds or more. One of these large examples can be seen in our Wonderland Express exhibition.

PHOTO: Shelf fungus on display in Wonderland Express.

Shelf fungus on display in Wonderland Express

PHOTO: Ganoderma lucidum fungus.

Ganoderma lucidum

It should also be noted that these shelf fungi have some aspect to them that are of interest other than their role in decomposition: while most species are woody and unpalatable, the chicken of the woods (Laetiporus sulfureus), is considered one of the best fungi for eating. There are also several species of shelf fungi thought to have medicinal properties, including the attractive Ganoderma lucidum (known as reishi in herbal medicine).

So next time you are out hiking in one of our local forest preserves, consider the “shelf life” around you, and what the woods—and life—would be like without them.

Find out more about the natural world at the Garden and in your backyard: learn about Lepidoptera, bats, and grubs.


©2015 Chicago Botanic Garden and my.chicagobotanic.org

I am sure that most of you know what I am referring to when I say “leap year.” Although this is not a leap year, I am suggesting that we unofficially call 2015 “Lep Year”—“lep” being short for Lepidoptera (from the Latin “scaly wing”), the order of insects that includes butterflies and moths. It has probably been a decade or more since I have seen the diversity and abundance of butterflies and moths that I have seen this past spring and summer.

PHOTO: Euchaetes egle (Milkweed tussock moth).

These voracious Euchaetes egle caterpillars were shredding some of the common milkweed plants near the prairie at the Garden this summer.

Lately, the butterflies have gotten the lion’s share of PR. In particular, the monarch butterfly is on nearly everyone’s radar, due to its precarious situation with dwindling wintering grounds and lack of larval food plants—the milkweeds. However, if you compare the two groups, butterflies and moths, the numbers of moth species outnumber the butterflies by more than ten to one in North America! In fact, there is a moth species that is also dependent on milkweeds—the milkweed tussock moth (Euchaetes egle). The caterpillars of this species are black and orange (a similar color combination to the monarch), and they usually occur in large numbers when you find them. The black-and-orange coloration signals to predators not to eat these fuzzy little fur balls.

The main difference between butterflies and moths is that the moths, in general, tend to be rather drab colored and active at night while the butterflies are mostly colorful and active during the day. These are generalities since you can find very colorful moths, rather drab butterflies, and a number of day-flying moths. There are also structural differences most easily seen in their antennae. While butterflies have narrow antennae with club-shaped structures at the end, the moths can have either thread-like antennae that end in a point in females or fern-like antennae in males. The fern-like antennae of the males are used to detect the chemicals, called pheromones, released by the females when they are ready to mate. Some moths can follow these chemical trails for miles.

Sixty percent or more of the diet of some nestling songbirds comes from caterpillars, and these are most certainly moth caterpillars.

Moths are not only extremely diverse in shape and pattern, they also have a wonderful variety of common names that people have come up with to label them. There are sphinx moths or hawk moths, daggers and darts, army worms and prominents, sallows and quakers, owlets and loopers, and marvels and bird-dropping moths. The names go on and on, some attempting to describe the adults and others the larvae.

PHOTO: Cecropia moth caterpillar (Hyalophora cecropia).

This brightly ornamented Cecropia moth caterpillar (Hyalophora cecropia) will turn into North America’s largest native moth.

It is hard to say which stage of the moth life cycle is more impressive. Although the adult moths are so varied in their shape, size, and patterns, the caterpillars are no less amazing. Take for example the strikingly beautiful brown hooded owlet moth caterpillar.

PHOTO: Brown hooded owlet caterpillar (Cucullia convexipennis).

The brown hooded owlet caterpillar (Cucullia convexipennis) is a stunning specimen to find outside my office.

It would be difficult to find a more attractive critter anywhere, and here it was, right outside my office. Equally impressive are the huge silkworm caterpillars. The Cecropia moth caterpillar (Hyalophora cecropia) is almost shocking, not only because of its massive size, but also because of the large orange-and-yellow spiky beads covered in black spots along its back and the smaller turquoise-spiked beads ornamenting its sides.

And who could talk about moth caterpillars without mentioning the infamous woolly bear? These orange and black-banded caterpillars are often consulted to see what the winter will be like. Unfortunately, the banding on the caterpillar has nothing to do with the weather, but at least it has gotten it a lot of attention. The woolly bear eventually turns into the bright orange Isabella tiger moth (Pyrrharctia isabella).

PHOTO: Woolly bear caterpillar (Pyrrharctia isabella).

Who hasn’t been tempted to touch the woolly bear caterpillar (Pyrrharctia isabella)? Photo by By Micha L. Rieser via Wikimedia Commons

PHOTO: Isabella tiger moth (Pyrrharctia isabella).

The Isabella tiger moth retains its orange-and-black caterpillar coloring. Photo by Andy Reago & Chrissy McClarren via Wikimedia Commons

The high diversity and nocturnal behavior of moths make it not unlikely that you might find a moth or caterpillar you haven’t seen before. The other day, while trimming my rambunctious Virginia creeper vine on the side of my house, I spotted an interesting caterpillar that I had never seen before. As a woodland ecologist I have experience with a lot of caterpillars, so it is always interesting when something new comes along. As it turns out, the caterpillar was the larval stage of an Abbott’s sphinx moth (Sphecodina abbottii). Although this was a new find for me, I still have not seen the adult moth.

Every morning when I come into work, I check the wall outside our building under the light to see if any new moths have shown up during the night. Some of the moths I have spotted this summer are the Crocus geometer, Colona moth, Ironweed borer, large maple spanworm, Ambiguous moth, green owlet, and one of the microlepidoptera, the morning-glory plume moth.

PHOTO: Colona moth (Haploa colona).

Colona moth (Haploa colona)

PHOTO: Crocus geometer (Xanthotype urticaria).

Crocus geometer (Xanthotype urticaria)

PHOTO: Green owlet (Leuconycta diphteroides).

Green owlet (Leuconycta diphteroides)

PHOTO: Morning glory plume (Emmelina monodactyla).

Morning glory plume (Emmelina monodactyla)

PHOTO: Ironweed borer (Papaipema cerussata).

Ironweed borer (Papaipema cerussata)

Most moths do not live for very long as adults. Ironically, some of the largest moth species live the shortest lives. I had the opportunity to see a new species of one of these megamoths for the first time this summer when my wife brought home an Imperial moth (Eacles imperialis) that she found clinging to the window of the school where she works. The very large moths in the family Saturniidae (silkworms and royal moths) emerge either from the soil, in the case of the Imperial moth, or from one of the familiar large cocoons you can find attached to a twig, like those of the Cecropia or Promethea moths. Since these moths do not have functional mouth parts, they are unable to feed, so they live off their stored body fat while searching for mates until they die, usually within seven to ten days.

PHOTO: Imperial moth (Eacles imperialis).

This Imperial moth (Eacles imperialis), had a 5-to-6-inch wingspan, and a body as big as my thumb!


Interested in finding out more? Visit the Moth Photographers Group at mothphotographersgroup.msstate.edu or BugGuide at bugguide.net.

Another new species for me was the painted lichen moth. While removing Japanese beetles from my hazelnut shrubs, I spotted what looked like a large firefly. As it turned out, it was not a firefly at all, but rather a moth that mimics one. Since fireflies are toxic to most predators, the moth gets a benefit from looking like the firefly. Another neat trick they employ is a maneuver known as frass flicking. They are able to expel their excrement nearly a foot away from their body. This is important because some predatory wasps locate their prey by homing in on the scent of their droppings.

There are a number of moths—or more accurately, moth larva—that are pests for gardeners. Almost all vegetable growers have run into cutworms at one time or another. Cutworms were given this name because of their habit of cutting off seedling plants in the garden. There are a number of cutworm species native to this country, but all develop into moths later in their life cycle.

PHOTO: Parasitized sphinx moth caterpillar.

The white structures on this parasitized sphinx moth caterpillar are the cocoons of the braconid wasps.

Another familiar larva is the tobacco or tomato hornworm (Manduca sexta). These are the large green larvae of one of our native sphinx or hawk moths. The Carolina sphinx larva is often found on tomatoes. Although they will rapidly chow down on tomato plant leaves, I generally leave them alone until they have had their fill and work their way down into the soil where they pupate to spend the winter. (I find that they rarely put much of a dent in the productivity of my tomato plants.) If you should happen to dig up one of their pupae when turning over the garden soil, they are a dark, shiny brown, pointed at one end, and have what looks like a teapot handle on the side that houses a long, curved proboscis. If you pick them up, you might be startled by the fact that they often times will swivel around at the middle—probably a predator avoidance behavior. Tobacco hornworm and sphinx moth caterpillars commonly fall prey to braconid wasps, which parasitize them. Leaving these parasitized caterpillars in the tomato garden can be an effective method of pest control.

PHOTO: Female gypsy moth (Lymantria dispar).

Female gypsy moth (Lymantria dispar)

A more serious pest species is the introduce gypsy moth. These moths occur in huge numbers and are capable of completely defoliating adult oak trees over large areas. A few years ago, we avoided an invasion of gypsy moths at the Garden when hundreds of thousands of these moths, in Turnbull Woods forest preserve across Green Bay Road in Glencoe, succumbed to a cool, rainy spring.

Join me and take advantage of this Lep Year—check out the yard lights, hedgerows, and flower beds, and see how many moths, caterpillars, and cocoons you can find!


Photos ©2015 Jim Steffen unless otherwise noted.

©2015 Chicago Botanic Garden and my.chicagobotanic.org

Echoes of a Silent Night

Senior ecologist Jim Steffen describes his close encounters with curious and beautiful bats.

Jim Steffen —  October 29, 2014 — 2 Comments

A few years ago, in early spring, I was traveling through McDonald Woods at the Chicago Botanic Garden, searching for some of the flat-bodied crab spiders (Philodromus) that typically spend the winter in communal groupings under the loose bark of dead trees. Upon reaching a small stand of dead American elm trees, I began to lift the loose remaining bark away from one of the trees to see if any spiders were present.

As I gently pulled the bark away from the trunk, a tiny black hand reached up over the top edge of the bark. It quickly became obvious that there were more than spiders under this bark!

Although I was a little startled to have this hand slowly reach out in front of my face, I immediately realized that this piece of loose bark was the day roost of a silver-haired bat. The silver-haired bat is a medium-sized bat that is a dark chocolate brown or black with white hairs scattered among the dark hairs on its back. I gently released the bark so as not to disturb the napping bat any more than I already had. This is just one example of why it is important to maintain at least some dead standing trees in our woodland communities.

PHOTO: Silver-haired bat.

A silver-haired bat curls up tightly on a tree in McDonald woods. Photo by Jim Steffen

Even though bats are fairly common mammals in our area, since they are almost totally nocturnal, we don’t get to see them all that often—especially at close range, when we would be able to admire their delicate form and attractive appearance. Bats are in the order Chiroptera, roughly translated as “hand wing,” and are the only mammals that are actually capable of true flight (unlike flying squirrels—which we also have at the Garden). 

You might be familiar with another group of small mammals known as shrews. Shrews are mouse-like animals that are actually carnivores that feed heavily on invertebrate populations. Although bats may have varied diets around the world, here they are primarily insect eaters, much like shrews with wings.

When I was in college studying mammology, we used to go out at night and look for streetlights where there were large numbers of moths and other flying insects attracted to the lights. We would then take out our car keys and jangle them around to make high-pitched sounds with the keys clinking together. These high-pitched sounds would simulate the high-pitched sounds produced by the echolocation sounds produced by hunting bats to locate their prey. (Unless we are equipped with special listening devices, we are not able to hear the sound of bat echolocation.) Often times, many of the moths would begin flying erratically, or drop out of the air as though they had been struck with a stupefying charm from Harry Potter’s wand. These moths have evolved defensive tactics to help them avoid being eaten by bats by flying in erratic patterns or closing their wings and dropping if they heard the sounds of an approaching bat. 

PHOTO: Eastern Red Bat

An eastern red bat (Lasiurus borealis) clings to black landscape fabric at the back of one of the buildings here at the Garden. Photo by Jim Steffen

Many years later, while removing invasive garlic mustard from our oak woodland a few summers ago, I came upon an oak tree with a broken branch. All of the leaves on the branch had turned a bright reddish-brown that stood out against the backdrop of all the other green foliage. On closer examination of the branch, I spotted a female eastern red bat hanging upside down, in typical bat fashion, with its single offspring clinging to it. I don’t know if the bat was aware of it, but this dead branch provided the perfect camouflage for her rich color.

This made me think about how these mammals perceive the world. Do bats have color vision, and was this red bat able to tell that the dead branch would be such a good match for its own color? Most nocturnal animals tend not to have color vision, since color does them little good in the dark. Most bats are various shades of brown, black, or gray. (It is a different story for birds that are mostly active during the day and use bright colors as a means of attracting mates or advertising territories.)

PHOTO: Lasiurus cinereus (hoary bat).

Hoary bat (Lasiurus cinereus by Daniel Neal [CC-BY-2.0], via Wikimedia Commons

We have five species of bats that are likely to be seen at the Garden. Some of them are summer residents, like the little brown, big brown, and eastern red bat, while others are mostly migratory species, like the silver-haired and hoary bats that show up during their spring and fall migrations. Years ago, in the late fall, while using fine nets at night to capture owls for attaching U.S. Fish and Wildlife Service bird bands, I often caught many of the large, hoary bats migrating south for the winter. These large bats have an attractive frosted appearance with a mix of white and reddish hairs all over their bodies.

While I was studying birds in the tropical rain forest of Central America, I often encountered small colonies of bats hanging at eye-level, under the broad leaves of Heliconia plants. I think these wide, tent-like leaves were chosen mostly for the protection they gave the bats from the torrential downpours that occurred every day. However, the bats we find here are either solitary animals, like the red, silver-haired, and hoary bats that live solitary lives in the woodlands and forests, or they are colony-forming bats, like the little and big brown bats, that search out attics, barns, or large hollow trees where they gather in groups to raise their young.

Some of the bat species also search out caves or old mine shafts during the wintertime, where the subterranean habitat provides moist, stable conditions with above-freezing temperatures suitable for hibernation. It is possible to construct bat houses that, if placed in the proper locations, can attract and support colony-forming bats during the summer.

We have several of these bat house installed on buildings around the Garden. This summer, one of those houses contained half a dozen bats—probably little browns. It is best to place bat houses in full sunlight, since the bats have high body metabolisms and prefer very warm conditions for roosting during the summer. Think you’d like to build a bat house? Construction details can be found at the Bat Conservation International website at batcon.org.

PHOTO: Flying squirrel.

Another local flier, this very tame flying squirrel enjoyed a snack of walnut with his photo op. Photo by Jim Steffen

Bats are more than curious and beautiful creatures; they are also tremendously important components of a healthy environment. They are extremely important control agents of insect populations. Many of the insect species they eat are harmful crop pests, like army cutworm, or irritating or disease-carrying species like mosquitoes. Some bats can consume more than 1,000 mosquitoes in a single night! Bats are in trouble now for many reasons—not the least of which are climate change, exotic diseases like white-nose syndrome, and habitat loss.

Although bats are seldom seen and often have scary, erroneous wives-tales associated with them, we should be working hard to correct the problems that might lead to a truly silent night.

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