Countdown to Extinction for Little Brown Bats
Attracting North American Bats
Millions of homeowners across the United States and Canada keep nest boxes on their property in hopes of attracting families of birds each spring. But how many people do you know who have bat houses in their backyards? Most people haven’t even heard of artificial bat boxes, and it’s easy to understand why the notion of attracting bats to your yard might not be as popular as attracting birds. For one, we hardly ever see bats, since they are nocturnal, and most of us would agree that bats aren’t that pretty anyway. Bats don’t sing us pretty songs in the morning; the noises they make are too high-pitched for the human ear to detect, and all we are able to pick up are faint clicks, which are actually echoes of their high chirps.
Furthermore, many of us find bats to be downright scary. Reminiscent of mice and bearing rather grotesque faces, they flutter around at night when we can’t see them and therefore have a sinister, mysterious aura about them. We’ve all heard horrifying legends of vampires sucking human blood, and our parents taught us to watch out for bats since they might be carrying rabies. These dangers, however, are greatly exaggerated: there are no vampire bats north of Mexico, and while bats can transmit rabies, only a very small percentage of bats carry this disease. As long as you don’t approach bats or try to touch them, you have nothing to worry about.
Human Population Impact
As human populations have boomed over the past few centuries, bat populations have fallen, partially because of all the misunderstanding and fear surrounding bats. Why would you protect something if it has no value to you, or if it even poses a danger to you and your family? However, attitudes have been changing in the past several decades, as scientists have finally begun to understand bats better. As it turns out, bats are actually important components of a healthy ecosystem, and provide several benefits to humans. Most notably, as most of us now realize, bats eat tons - literally! - of insects which we consider to be pests. One bat can eat up to six hundred insects per hour - insects such as mosquitoes which are the true bloodsuckers we have to worry about, or the larvae of the corn earworm, a moth that causes billions of dollars of damage to corn and other crops each year.
Many bats are essential to the pollination of certain plants. For example, the lesser long-nosed bat of the Sonora Desert visits the flowers of the famous saguaro and organ pipe cacti at night, slurping up the sweet nectar within, and in doing so transfers pollen from cactus to cactus and ensures that these plants can reproduce. Although we have developed methods to artificially pollinate many of our crops, the wild ancestors of bananas, avocados, cashews, and many other fruiting trees are dependent on bat pollination. In the tropics, there are also many species of bats that eat fruit, and by carrying around the fruit and dropping the seeds elsewhere, they help the plant spread its seeds to different places which might be better for new growth.
Scientists have identified over 1300 species of bats across the whole world, in every continent except Antarctica. This makes them the second most diverse groups of mammals, after rodents. Their sizes range from the bumblebee bat of Southeast Asia, which weighs as much as one penny, to the golden-crowned flying fox of the Philippines, which weighs about 2.6 pounds and has a wingspan of nearly six feet! There are 44 species of bats in the United States and Canada, all of which are insectivorous except for several species in the deserts of the Southwest which feed on nectar. However, there is a much greater diversity of diet in other parts of the world. For example, the fish-eating myotis of coastal Northwest Mexico feeds mostly on fish and crustaceans. Other species prey on frogs, rodents, small birds, and even smaller species of bats!
Most of us already know that bats find their prey through echolocation, a technique similar to that of sonar. While in flight, bats emit a rapid stream of high-pitched chirps - up to an incredible 200 chirps per second - and listen for the echoes of these chirps. The closer an object is, the stronger and more rapid the echo. Though the big ears on bats may look silly, they are quite important to the survival of these creatures, enabling them to pick up on their own echoes as well as minute noises of predators. For example, scientists have found that a certain African species is able to hear the footsteps of a beetle on sand from over six feet away.
You have likely heard or used the phrase “blind as a bat,” but this is based on a huge misconception. Although most bats, especially insectivorous ones, rely primarily on their sense of hearing while hunting, most also have excellent vision which equips them for navigating at night.
We all know well that bats sleep upside down, most famously in caves but also in cavities within dead trees, rock crevices, abandoned mines, under bridges, and inside buildings if they can find their way in and out. Because bats are rather particular about where they roost (among other reasons such as protection from predators), they often congregate in large colonies numbering into the millions. You can find the largest bat colony in the world at Bracken Cave, Texas, which hosts over 15 million Mexican free-tailed bats. The entire colony emerges each night to feed over the surrounding farmland.
Like many species of birds, some bat species undertake seasonal migrations between the North and the South in order to escape cold winters that make it impossible to find insects. Other species of the cold North do not truly migrate, but instead fly up to several hundred miles each fall to caves where they huddle up with thousands of other bats from the region and hibernate the winter away.
Most North American bats mate in the fall. They do not form couples; they simply mate and then the male flies off and never has any further role in the process. Interestingly, although the female carries the sperm in her body all winter, fertilization and ovulation do not occur until the spring, once hibernation has ended or migration has passed. Pregnant females usually roost in their own colonies, separate from colonies occupied by males and non-breeding females. Pregnancy lasts from one and a half to two months in most species, and females typically give birth to a single pup, although twins are not uncommon. The female then feeds her pup for about three weeks until it is able to fly and hunt for itself.
Over the past several hundred years, bat populations have declined worldwide for a variety of reasons, and the US Fish and Wildlife Service lists 9 of our 44 species as endangered. With the expansion of agriculture, logging, and urbanization, we have destroyed much bat habitat, particularly the dead trees, or snags, which they depend on as roosting sites. Application of pesticides over fields and along bodies of water where bats forage for insects has likely contributed to the decline.
Another threat comes from disturbance of caves where they roost. When people enter caves hosting hibernating bats for sport, exploration, or even mining bat guano, they often wake up the bats, causing them to expend precious energy which they were counting on in order to get through the winter. If disturbed too much, they may starve and die. Additionally, people have increasingly been closing off caves and abandoned mines with gates, largely in order to keep people out for their own safety, but with the unintended consequence of closing off bats from their roosting sites. Conservationists have been working with property owners in order to make sure that gates over caves and abandoned mines are able to let bats in while keeping humans out.
The Greatest Threat To Bats
Today, the greatest threat to bats in the United States and Canada is a disease called White-nose Syndrome (WNS), which first emerged just as recently as 2007 in a cave in New York. Caused by a fungus native to Eurasia, Pseudogymnoascus destructans, this disease has rapidly spread across the entire eastern US and Canada, and in 2016 researchers discovered that it has spread across the continent to the state of Washington. In short, WNS disrupts the physiological processes of the bats during hibernation and causes them to become active and senselessly move about in very cold temperatures. This quickly takes a toll on their fat reserves and causes them to starve. For more information, you can watch this short documentary video produced by the Forest Service, titled “Battle for Bats: Surviving White-nose Syndrome.”
Although scientists do not know of anything that you or I can do to fight WNS, there is one way you can lend a hand to bats in your area: installing bat boxes! Because we have cut down so many of the old, dead trees around our towns and countryside, bats have lost much of their natural roosting habitat. Our backyards may be abundant in insects, yet have no bats, simply because there is no suitable structure in the neighborhood for bats to call home. Bats thrive near bodies of water, so if you have a pond, lake, or stream near your home, you are in an especially good position to install bat boxes.
How To Mount a Bat House
You should mount your bat house 12-20 feet off the ground on the side of a building, in a place where the box will get plenty of sunlight, especially in the morning hours. This is important so that the bats will stay warm will roosting during the day. Make sure there are no nearby lights that will be kept on at night. Also, if possible, keep the box at least twenty feet away from roads where the bats might be struck by cars, as well as tree branches, wires, or other potential perches of aerial predators such as hawks and owls. Once installed, simply be patient and hope that bats will discover the house, and be sure to check the box every so often to make sure that wasps or hornets don’t take it over.
To learn more about bats, see what species you have in your region, and stay informed with news about bat conservation, the non-government organization Bat Conservation International is a great resource.