Vol. 12 Issue 2, Summer 2007
By Nicole Hamilton
This article was compiled from a number of sources (listed at the end of the article) as well as with help from Leslie Sturges of Bat World Northern Virginia. To read Part 1 of The Bats of Loudoun, click here:
Bats are an ancient species that has been around for 45 million years, yet their appearance has stayed about the same. While there are over 1,100 species of bats worldwide, here in Loudoun we are known to have 7 species. Indiana Bats may eventually be found in western Loudoun, but they are a federally endangered species and therefore are very rare.
- Little Brown Bat (Myotis lucifugus). Little Brown Bats are one of our most common species. They are small, approximately 3½” long, and have glossy, dark yellow-brown to olive-brown or even chocolate-brown fur. Little Brown Bats mate in fall with fertilization delayed until spring ovulation happens after they emerge from hibernation. Nursery colonies, which can be as small as just several females to thousands, form in late April – May in warm, dark locations. These bats use a variety of summer roosts, including buildings, tree cavities and crevices, tunnels, abandoned mines, and cliffs. Males are solitary, roosting in hollow trees, under loose bark, and in other crevices. This bat is the species most likely to be found near people’s homes and in bat houses. Little Brown Bats forage at late dusk and often repeat hunting flight patterns. They may use waterways or even highways for orientation along their hunting route. They forage about 10 – 20 feet over trees, lawns, and pastures and 3 – 6 feet over open water. Just one Little Brown Bat can eat up to 1,200 insects in an hour of peak feeding activity. Moths make up a major part of their diet, in addition to mosquitoes, flies, beetles, midges, mayflies, and aquatic insects. In October and November, these bats move to their hibernation sites, gathering in caves, tunnels, and mine shafts. They may disperse to several hibernacula, and the hibernating colony may come from many summer colonies. Bats use the same hibernation and nursery sites year after year. Hibernating Little Brown Bats can stop breathing for almost an hour to reduce energy needs. Little Brown Bats are found in much of the United States, Canada, and Alaska.
- Big Brown Bat (Eptesicus fuscus). As its name infers, this is a larger bat, with an average length of 4 – 5”. Big Brown Bats have long, glossy, dark-brown hair, a broad nose, and short black ears. Traditionally, Big Brown Bats formed nursery colonies beneath loose bark and in small tree cavities, but they have also adapted to using manmade structures as forests have disappeared. Today, nursery colonies are often found in barns, houses, and churches, as well as caves and abandoned mines. They have up to two pups per year and give birth from May to late June. Big Brown Bats are not migratory and sometimes use the same roost for summer and winter. In fact, it’s looking increasingly like Big Brown Bats may not go far at all — possibly from attic to basement or barn to garage! Predators include black rat snakes, screech owls, grackles, house cats, and bullfrogs. This is the most common bat to enter a house. Big Brown Bats are very efficient feeders that can fill their stomachs in an hour of feeding. They fly at dusk, and often go in a nearly straight course 30 feet in the air, often emitting an audible chatter. They are generalists in their foraging behavior and habitat selection, showing little preference for feeding over water versus land or forest versus clearings. Numerous studies have shown that Big Brown Bats consume significant numbers of crop and forest pests, including ground beetles, scarab beetles, cucumber beetles, snout beetles, and stink bugs. In one summer, a colony of 150 Big Brown Bats can consume enough adult cucumber beetles to prevent egg-laying that would produce 33 million of their root-worm larvae, a major pest of corn. These bats are among the last to hibernate, entering their hibernation sites in late October to November. Big Brown Bats clearly rank among America’s most beneficial animals. As we destroy their forested habitats, they will seek buildings and other manmade structures to roost in. By providing bat houses, we can keep bats out of our homes yet keep them close enough to benefit from their insect-eating and enjoy their presence. Big Brown Bats have been known to live19 years in the wild. They are found in most of the United States, Canada, and down into Mexico.
- Eastern Red Bat (Lasiurus borealis). This is a medium-sized bat, approximately 3½ – 4¾” long, with bright red to rusty long, silky fur. This is one of the few bats with contrasting color sexes. Females are dull, buffy chestnut with frosting, while males are almost orange-red. This is a tree-dwelling species that lives mostly in dense foliage and hibernates in the open or under leaf litter. Despite their reddish color, they are often hard to see when clinging to trees, since they blend in, looking like a fall leaf or pine cone. Red Bats are solitary except for mating and migrating, and females even roost singly when raising young. During the day, they hang by one foot with their tail membrane wrapped down around their bellies, twisting in the wind like a leaf. Red Bats have 1 to 5 young which are born from late May to early June. Unlike most bats, Red Bats often give birth to twins or triplets. During the day, pups hold on to their mothers with one foot and a perch with the other. Mothers leave their pups at night to forage but will move them to safer locations if needed. Pups begin flying at about 3 – 4 weeks and are weaned just a few weeks later. Red Bats fly in early evening and have been timed at speeds of 40 mph. They feed among trees in the forest, around lights in towns, and on the sides of barns; they eat both hard and soft insects, with moths being a favorite. They migrate south in late September to November, following the same Atlantic flyways as migratory birds. In the late 1880s, there were reports of large migrating flocks passing in daytime, but such sights have not been seen in more than a century. Red Bats live throughout the United States, Canada, and Mexico.
- Silver-Haired Bat (Lasionycteris noctivagans). This is a medium-sized bat about 3¾ – 4½” long with long, brownish-black, silver-tipped fur. Silver-Haired Bats depend on old-growth forest areas, and so managing forests for diverse age, allowing snags to stay in place, and maintaining forested corridors is critical to them. Mating is thought to occur in the fall, with delayed fertilization until spring. Females form small nursery colonies in tree cavities and small hollows and, like many forest-roosting bats, switch roosts throughout the maternity season. Two pups are born in late June to early July. Silver-Haired Bats fly slowly and at heights of 20 feet or more near mixed or coniferous forests adjacent to water. The males and females spend fall and winter in the same southern areas, but in spring, the females migrate further north than the males. They are frequently found around streams, rivers, and woodland ponds, with tree crevices being the most common shelters/roosts. Beetles are their principal food. Silver-Haired Bats feed earlier than most bats, often coming out just before sunset. Because they are tree dwelling, they are rarely encountered around homes although this sometimes occurs. They often hibernate in woodpiles and have been recovered from garages and, once, an airplane hangar. Life expectancy for Silver-Haired Bats is up to 12 years. They live throughout the United States and into parts of Canada.
- Northern Myotis (Myotis septentrionalis). The Northern Myotis is a medium-sized bat with a total length of 3 – 5”. It has no glossy brown fur, with its stomach fur being lighter in color than its back. Northern Myotis are forest bats, needing dense forest stands for their habitat. They forage on hillsides and ridge-forests rather than riparian and flood-plain forests. Little is known about the reproduction of this species, but similar to the Little Brown Bat, they are thought to mate in the fall. They give birth to one pup in June or July. Females form small colonies of up to 30 individuals, sometimes under bark and in tree cavities. They hibernate singly or in small clusters of 4 – 6 individuals or colonies of up to 350 individuals. Hibernation may begin as early as August, and they rely upon caves and underground mines for their hibernation sites. The record for longevity is 18½ years.
- Hoary Bat (Lasiurus cinereus). This is the largest of our Loudoun bats, with a length of 5 – 5½”. The fur is long and dark to light brown, with gray or silver tips, which gives a frosted (“hoary”) appearance. People rarely get to see these bats because they are not attracted to human structures and they stay well hidden in foliage during the day. They roost primarily in the foliage of trees, often near the edge of a clearing, 10 – 15 feet above the ground during the day. Females do not form nursery colonies as do some other bats but instead are quite solitary. Two young are born in mid-May to early June. Hoary Bats feed above trees, over water, and in forest clearings, emerging after dark and feeding from early evening to dawn. They sometimes make round trips of up to 24 miles on the first foraging trip of the night and then make several shorter trips, returning to the day roost about an hour before sunrise. They enjoy moths, mosquitoes, dragonflies, wasps, beetles, and grasshoppers. Hoary Bats are strong, swift fliers that are often found in the company of birds as they migrate along the same routes. The sexes remain separate during the summer but then migrate south together in waves, migrating to subtropical and possibly tropical areas to spend the winter. This species is found across the United States and throughout Virginia, but interestingly, most of the Hoary Bats found in Virginia are female. The Hoary Bat is most often encountered during migration periods, as most seem to go farther north to give birth.
- Eastern Pipistrelle (Pipistrellus subflavus). This is one of the smallest eastern bats, with a total length of 2¾ – 3¾”. It has yellowish-brown tricolor fur, which, along with the small size, distinguishes it from other bats. There are two, rarely one, young born in sex-segregated maternity colonies from mid-June to early July. They are active until late October, and hibernate in caves/mines often too tiny for other species. There are one to several hundred per cave, some hanging singly scattered about but preferring warm sites in protected passages. Individuals may occupy a precise spot each winter. They may roost in caves, rock crevices, trees/foliage, and seldom buildings. This species forages in early evening in treetops, often over water. Their life span is 4 – 8 years in the wild.
The Future of Loudoun’s Bats
As reported by our own Bat World NOVA, while most of our bat species are not yet threatened, they are all suffering dramatic population declines. Bats’ habitat and foraging areas disappear as woodlands are cleared and farms are developed. Aquatic insect populations on which our bats prey become scarcer as waterways are polluted or eroded. Habitats become unusable when standing ponds or wetlands are destroyed, because bats must roost within ¼ mile of a water source. Pesticides destroy the insects bats rely on and poison the bats themselves. Pets, particularly cats left outdoors, maim and kill thousands of bats annually. And finally, human attitudes cause thousands of bats to be evicted from the few remaining roost sites they’ve found — usually wooden structures such as houses, barns, and garages. Bats are routinely killed out of hand if they’re found near human habitation because of overreaction about public health concerns or unfounded fear and superstition. You can help bats in several ways:
- Install a bat house. Plans for building multi-chamber houses, which are the ones that work the best with our Loudoun species, can be found online at http://dnr2.maryland.gov/wildlife/Pages/plants_wildlife/bats/batboxes.aspx. Bat houses sold in bird and garden supply stores typically do not work because they are single chamber or too small. You can learn more about bat houses online at the Bat Conservation and Management website (www.batmanagement.com), which shows why most commercial boxes don’t work. They do, however, sell kits that are very good and are recommended by Bat World.
- Turn off that bug zapper! Bats do a better job, and bug zappers kill insects indiscriminately. You are taking out the good along with the bad when you use a bug zapper.
- Install a pond or water garden. In addition to beautifying your yard, you’ll give bats a place to get a drink of water. A healthy pond will support a population of aquatic insects for your bat to dine on as well.
- Let dead trees stand. If there is no danger to persons or buildings, leaving dead trees, called snags, standing provides habitat for bats, cavity-nesting birds, small mammals, and bark-dwelling insects.
- Attend an educational program to learn more about bats and other native wildlife.
Bats in Boxes
Bats are faithful in returning to both their winter/hibernation roosts and their summer/ nursery roosts, so if you are setting up a new bat house, it may take some time for the bats to take up residence. Bat houses have about a 50 percent success rate, so patience is in order. Install your bat house in the winter or spring. This will allow the bats in your neighborhood to become familiar with the new roost over the coming summer. They may not use it immediately but will check it out.
During this first year, you may have a solitary male or two use the box for roosting. The following spring, when the female bats return they may decide to use the new roost. This typically happens when their traditional nursery roost has been destroyed or is uninhabitable or outgrown. Colonies identify their roost partly by their smell. A new bat house will smell of new materials.
As the house weathers outdoors, it will take on a more natural scent. Larger bat houses are more successful than smaller ones. Other important tips such as how high the bat house should be posted, the direction it should face, and other success tips can be found at www.batcon.org.
There are two situations in which people and bats find themselves in conflict: (1) when a single bat enters a house, and (2) when a nursery or maternity colony roosts in a building. Both of these situations can be solved without killing the bats. Information and detailed instruction on the proper techniques for dealing with these situations can be found on the LWC website at www.loudounwildlife.org/Books_Resources_Mammals_Bats.htm.
Sources and Resources Used to Compile This Article:
A Homeowners Guide to Northeastern Bats and Bat Problems,Penn State College of Agricultural Sciences
Bat Conservation International Educational Materials, www.batcon.org
Bats, West Virginia Extension Service, West Virginia University, Norma Venable, 1999
Species Accounts, Virginia Department of Game and Inland Fisheries website: http://dgif.virginia.gov/wildlife/bats
Bat World , www.batworld.org