The Eureka Moment!
Originally published by Village News, a publication of the community of Cabin John, MD. As a bat researcher, I used to think that there were two kinds of people in the world: those terrified by bats and those odd few who adored them. My own baseless fear of bats throughout adolescence and into early adulthood kept me rooted among the first group. I confess to killing harmless pipistrelles—bats no longer than my index finger—that dared to nest in the thatch roof of my hut in Nepal; I still cringe at the memory. In graduate school on a tropical biology course in Costa Rica, I was introduced by an enthusiastic bat biologist to the wonders of these flying mammals, the only group capable of this feat. I met bats that pollinated flowers and dispersed fruits, and bats that scooped fish out of the water with their feet, those that homed in on singing male frogs or katydids and carried them off, and even bats that ate birds or other bats, the tigers of their kind. I now found them beautiful, graceful, and exquisite designs of nature. I had been converted.
I reflected on my late transformation as I sat on my Cabin John veranda watching some little brown bats and one big brown bat swoop and swivel above my garden in the twilight, catching insects on the wing. These are the proletarian bats that do the bulk of the mosquito, moth, and beetle eating in our neighborhood. Some day, I hope to see the king of the local bat community hawking insects at night or hiding in the day amidst the foliage of a tree in the backyard, the poorly named “hoary bat” (Lasiurus cinereus), one of the most beautiful mammals in the world. The “hoary” characterization refers to the frosted appearance of its pelage. The bat’s reputation would have fared better if a clever taxonomist had called it the “fashionable bat” or the “exquisitely furred bat.” Hoary will have to do.
This small bat that weighs no more than three twenty-five cent pieces is migratory and one of the most widespread mammals in North America, although never common anywhere. Bats as a group, however, are everywhere and, with over 1,200 species named, they are second to rodents (with around 2,000 species) as the most diverse among the 5,200 species of mammals. Bats are often the most abundant mammal at any site in the tropics, and it is when you visit tropical islands that their significance becomes plain. The hoary bat is the only native mammal in the Hawaiian Islands besides the Hawaiian monk seal and, in the Galápagos archipelago, it is one of the few native mammals (along with four species of rice rats and a second bat species, a close cousin of hoary bat). On the island of New Caledonia, about 2,000 miles off the Australian Coast in the Coral Sea, the only native land mammals are bats. A pattern emerges here and an interesting tale of biogeography—the branch of science concerning the ranges of plants and animals. Why did only rice rats and bats make it to the Galápagos and only bats to other islands? Rice rats rafted over from mainland South America on floating mats of vegetation, but the bats flew the 600 miles or were assisted by the tropical winds. The reason that no other land mammals make it on their own to most islands is that we land mammals—Diana Nyad notwithstanding—are terrible long-distance swimmers. And even English Channel adventurers can’t drink seawater. That is the rub—most mammals would die of thirst before reaching the shore of an island more distant than a few miles from the mainland.
In Costa Rica and Panama, I studied fruit bats for my doctorate, not just because I found them fascinating, but because they provide such a vital role in pollination and seed dispersal. Bats are known to disperse the seeds or pollinate the flowers of some 450 plant species. Bats pollinate bananas, cocoa, and agave—the latter producing that college party staple—tequila. Evening bats in Southeast Asia are the only natural pollinators of durian—the world’s most expensive fruit, which has been described as tasting like heaven but smelling like the sewer.
But it is the group of hoary bats that gave me the thrill of a lifetime as a biologist. Those plying my trade all hope for the sighting of something new, something you were the first to find in a lifetime of fieldwork, when you can literally shout “Eureka!” My Eureka moment came one windy night on the Continental Divide in Costa Rica, at about 5,500 feet elevation. I had strung monofilament nets across a low point on a trail that served as a mountain pass. Bats began arriving and after catching, identifying, and releasing them, I came upon one I had never seen before—a yellow version of the hoary bat—a first for my area and Costa Rica. And then another bat flew into the net, sporting the most luxuriant fur I had ever seen on a mammal. It looked just like a hoary bat but its rich red, chestnut, and black fur convinced me I had found something entirely new. It turned out to be Lasiurus castaneus, a first for Costa Rica and Central America and rarely seen anywhere in the New World. This species is so rare it has no formally recognized common name, but I propose the “chestnut-robed bat.”
The chestnut-robed or yellow version of the hoary bat will never visit my backyard, but my bat house is up, and I keep a vigil. You never know when the next Eureka moment will strike.
A Taste for Tree Bark
Originally published by Village News, a publication of the community of Cabin John, MD.
The banks of the Potomac can be a peaceful setting for a picnic on a warm spring evening. As my wife and I were taking in the view of the river from one of the sandy Potomac beaches below Lock 8, something caught my eye. A large headed object was breaking the surface of the river and headed straight towards us. It wasn’t until the creature crawled onto the bank that I identified our visitor from the Virginia shore—a beaver.
The beaver shook the water off its dense coat and walked closer. It turned sideways so we could make out its distinguishing feature, a broad flat tail that is used as both a powerful oar and rudder and a way to communicate danger by slapping it on the surface of the water before diving below. A good-sized beaver can reach 55 pounds, making it the largest rodent second only to the massive capybara of South America, another river-dweller. This was a big fellow, or maybe a female, for unlike in most of the other 5,200 mammalian species, beaver females are often larger than males. We remained motionless while the beaver approached our blanket. It came within a few feet and then stopped and headed off into the riverbank forest, ready for another evening of work.
Beavers are nocturnal, like most mammals. But it is in the bright light of day, when they are safely asleep in their lodges, that we see the extent of their creation, or destruction, depending on your perspective. Along the trail bordering upper Cabin John Creek between River Road and Bradley Boulevard, for example, fresh signs of beaver are hard to miss. Here, groups of trees have been reduced to the tell-tale pointed stumps that can turn the riverbank into an otherworldly landscape.
Beavers take down trees and stems to construct dams and lodges. The purpose of the dam is to flood an area around a lodge—like a wide, deep moat—and make it difficult for its predators to reach them. In the safest spot they build their lodge with sticks and mud that becomes a shelter—impregnable from above and only accessible through an underwater entrance. The large interior is highly functional: there is one platform where a wet beaver can shake off the water from its coat, and another perch where the now dry beaver clan can cuddle and sleep.
The inside of the lodge has attracted the attention of architects, but it is the landscape architecture surrounding the lodge that garners the interest of ecologists. Simply put, next to humans, the North American beaver is the most influential landscape engineer north of Mexico. Through its networks of dams, beavers change water levels, create swamps and breeding areas for local fish and the fish predators that hunt them, draw in other species like muskrats, and mink, otter and fisher. And they don’t take Sundays off. Beavers are relentless builders and handymen; if their lodges or dams are damaged one night, they will be back repairing them the next night. In fact, the influence of beavers on the habitats of so many other species—from fish to frogs to aquatic plants, nesting birds and other mammals, some of which are listed as endangered species—is so pervasive that ecologists consider this landscape engineer a “keystone species.” A keystone species is one whose effect on the ecosystem is disproportionate to its actual abundance and whose removal would lead to dramatic changes in the local surroundings. Beavers also help maintain water quality and availability. The wetland networks they create through damming soak up floodwaters, and release water more slowly in times of drought. Beaver infrastructure also reduces erosion, raises the water table, and even purifies water. The silt collected above old dams sequesters toxic pesticides and other harmful compounds where they can be broken down by microbes.
Beavers have also played a central role in U.S. history. Some authors argue that the settlement of North America was driven in large part by pursuit of beaver fur. In Cabin John as in Canada and much of the lower 48, beavers were virtually wiped out by the early 1900s by pelt hunters. The European Beaver, a different species, was completely extirpated over most of its range. Thankfully, extensive recovery efforts and protection from over-exploitation has led to a recovery here in the U.S., although beaver still have reclaimed only about 10% of their historic range.
Looking over the markings left by a working beaver, it’s a marvel that their teeth don’t wear down quickly and result in a short life and a mouth full of splinters. Just the opposite is true. Beaver can live to be 25 years old and their chisel sharp incisor teeth never stop growing. Rather than being rooted like our teeth, they are rootless. Beaver love to eat water lilies and fruit, but their meat and potatoes is the soft green tissues of trees.
The shores of the Potomac have been shaped by beavers for eons but for a short period of several hundred years when we drove them to local extinction. Now they have regained lost territory. The same cannot be said for their extinct distant relatives, the Giant Beaver of North America, which may have roamed Cabin John until about 10,000 years ago. Biologists assume they disappeared before early hunters arrived. The giant version probably wouldn’t have lasted long anyway, standing seven feet tall and weighing close to 300 pounds; its fur and meat would have made it a desirable target. I still would have liked to have seen one cross the Potomac.
Feeding the Hawks
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