VESPERTILIONIDAE

Evening bats

Biology

  One scheme (Wilson and Reeder, 1993) employs the following subfamilies: Kerivoulinae (genus Kerivoula), Murininae (Murina and Harpiocephalus, both with tube-like nostrils), Miniopterinae (genus Miniopterus, these have very long 3rd fingers), Tomopeatinae (Tomopeas, with thick, leathery ears like the molossids), Vespertilioninae (all the other genera). Vespertilionids, or evening bats, have small eyes, no noseleaf (rudimentary in Nyctophilus and Pharotis), and ears with both a tragus (fleshy ear outgrowth) and an anterior basal lobe (except Tomopeas). Their tails are relatively long and extend to the edge of the tail membrane or beyond. This large family includes a wide range of sizes. Some vesper bats weigh only 4 grams as adults, whereas others weigh up to 50 grams. Most of these bats are black or brown colored, but some are orangish or have other markings.

  Morphologists identify vespertilionid bat skulls by the unfused premaxilla, the trend towards short jaws, and the absence of any postorbital process. The number of teeth in this family varies from 28 to 38 depending on the species. The dental formula is 1-2/2-3, 1/1, 1-3/2-3, 3/3. The premolars and molars are dilambdadont. These bats are primarily insectivorous, and most hawk insects in flight, often using their wings like tennis rackets and swatting the insects into the tail membrane. Some species eat fish (Pizonyx, Myotis spp.), and most species defend a feeding territory.

Ecology

  Many vespertilionids live in caves, but these bats can also be found in mine shafts, tunnels, old wells, rock crevices, buildings, etc. Some species contaminate man's habitations with feces and noise, but this annoyance is more than offset by the bats' consumption of huge quantities of insects. Some species roost in large colonies, but others are solitary or live in small groups or pairs. Males and females tend to roost apart most of the year, and some species have maternity colonies. The mating system varies widely within the vespertilionids. Many species show resource defense polygyny, the most common mating system in bats. Other vespertilionid mating systems include promiscuity in Myotis lucifugus and lekking in some Miniopterus species.

  This group of bats has a worldwide distribution. Vesper bats live in tropical forests, deserts, and temperate zones -- only polar regions and some remote isles are vespertilionid-free. The vespertilionid genus Myotis has the widest distribution of all bat genera. Temperate zone bats are faced with a dilemma when cold weather drives insects away. Some species (Lasiurus, Lasionycteris, Nyctalus, some Pipistrellus) migrate to areas where there is more food, while many other species of vespertilionids hibernate. Hibernating bats lower their body temperatures and remain inactive for several days or even months at a time. They often hibernate in caves where the ambient temperature does not fall below freezing. These bats then drop their body temperature to as low as 2 C. Since maintaining a high body temperature requires using up many calories, these bats save a lot of energy by lowering their body temperature in hibernation. These bats survive the winter by living off fat stores and making occasional foraging trips during warmer weather. Hibernation is known in at least some species of the following genera: Antrozous, Eptesicus, Miniopterus, Myotis, Nyctalus, Pipistrellus, and Plecotus. Many hibernating species and a few non-hibernators delay giving birth until spring or summer, when food is plentiful. Vespertilionid bats typically mate in the fall.

  They then postpone birthing by three different methods. Females from many species of vespertilionids store sperm in the uterus from fall matings throughout the winter. The females ovulate in the spring and give birth in late spring or early summer. Miniopterus females do not store sperm; instead, they delay implantation of the blastocyst, which remains free in the female reproductive tract until environmental conditions improve. Finally, in some Eptesicus, Miniopterus and Myotis females, the blastocyst implants in the uterus, but further development is delayed until spring. The reproductive and physiological adaptations described above allow vespertilionid bats to succeed in temperate as well as tropical zones. This family shows extraordinary variability in mating, reproductive, and seasonal strategies. Vespertilionids also show a wide range of wing shapes, roosting behavior, and foraging strategies. These bats have been successful world wide.

Behavior

Hoary Bat

 

Hoary bats are solitary. They roost 3 to 5 m above ground during the day, usually in the foliage of trees. They prefer dense leaf coverage above and an open area below. They also prefer trees that border clearings. They have been seen roosting in a woodpecker hole in British Columbia, in the nest of a gray squirrel, and under a driftwood plank. Occasionally they are found clinging to the overhangs of buildings and in caves in the latter part of the summer. They often have trouble finding their way out of the caves and die there.

Hoary bats reach their peak activity at about five hours after sunset, although they may occasionally be seen flying on warm winter afternoons. Their flight is stong and direct, reaching speeds of thirteen miles/hr. While hunting, they soar and glide. They forage about the tree tops, along streams and lake shores, and in urban areas where there are lots of trees. The bat stops to rest between meals at night. Feeding is the only time that the hoary bat appears to associate with other bat species. Hoary bats often form groups when hunting for insects.

The bat wraps its hairy tail membrane around its curled up body for insulation while resting during harsh weather conditions. It becomes torpid when inactive during the day, as well as between feeding flights at night. When it is resting and non-torpid, the bat has a metabolic rate of 1.19 cc of oxygen per gram of body weight per hour.

Like all microbats, the hoary bat uses echolocation while flying. It makes a shrill, hissing sound when disturbed. It is one of the only vespertilionid bats which makes an audible chatter during flight.

The hoary bat can be seen flying in large groups in spring and autumn, during the time of breeding and migration. They are believed to migrate through Florida from late October to late November and from February through early May. Autumn migration occurs in waves, whereas spring migration appears to be less organized. Some hoary bats are believed to remain in the north and hibernate for the winter, rather than moving south of the United States like most do.

Distribution - Conservation

Researchers disagree as to the bat's preference for coniferous versus broadleaf trees. Hoary bats are thought to prefer trees at the edge of clearings, but have been found in trees in heavy forests, open wooded glades, and shade trees along urban streets and in city parks. They live in temperate forest & rainforest, temperate grassland, chaparral, desert, tropical rainforest, tropical deciduous forest, tropical scrub forest, tropical savanna & grasslands. Hoary bats prey on many insect species that are considered to be pests.  he hoary bat occasionally hangs out under overhangs of houses and garages, but this is only menacing and they rarely cause any true disturbance to homeowners. The bat has a relatively high incidence of rabies. In some years, 25% of sick bats collected were found to be rabid. The hoary bat's main enemies are hawks and owls. American kestrals and rat snakes have on rare occasions been reported to feed on hoary bats. The bat is also known to become entangled in barbed wire fences. Another important source of mortality is females falling out of their roost with attached young, thus becoming easy prey for terrestrial passers by.

The bat is often infested with mites (Pteracarus chalinolbus and Chiroptonysus americanus), helminths (Longibucca lasiura, Oochoustica taborensis, and Physocephalus), and protozoa (Distoma).

Hoary Bat (Lasiurus cinereus)

  The hoary bat is the most widespread of all bats in the United States. Though not yet recorded in Alaska, the bat is thought to occur in all 50 states. It ranges from the tree limit in Canada down to at least Guatemala in Central America, and throughout South America. They are the only bats found in Hawaii. There are records of migrant hoary bats on Southampton Island off of Northern Canada, and from Iceland, Bermuda, and the Orkney Islands off Scotland. They are rare in most of the eastern United States and northern Rockies and common in the Pacific Northwest and prairie states. They are abundant in California, Arizona, and New Mexico, where they winter. They winter in southern California, southeastern United States, Mexico, and Guatemala, but have also been found in Michigan, New York and Connecticut during December and in Indiana during January. This suggests that some may winter farther north than was previously expected.

Sexes are generally only found together in parts of Nebraska, Montana, and the Badlands of South Dakota. Males and females are usually separated during the warmer months in North America, except during the mating season. Females appear to be more concentrated in the western part of North America. There is evidence for an altitudinal separation of sexes in California, with females concentrated in the lowlands and coastal valleys and males higher up in the foothills and mountains.

There are three subspecies of Lasiurus cinereus: cinereus in North and Central America, semotus in Hawaii, and villosissimus in South America.

Mass: 20 to 35 g. The body of the hoary bat is about the size of a fat mouse. The length from the tip of the nose to the end of the tail vertebrae is 5 1/8 to 5 7/8 inches. The wingspan is 17 inches. The bat has a blunt, rounded nose and small, beady eyes. The ears are short, thick, broad, and rounded. When laid forward they do not reach the nostrils. The tragus in the ear is short and blunt. The hindfoot is half as long as the tibia and has thick fur on the dorsal side. The thumbs are long. The calcar is twice as long as the hindfoot and is narrowly keeled on the posterior edge, bearing lobes on the tip. The bat has four mammary glands.

Thick, long, soft hair covers the entire dorsal surface extending to the elbow, the median ventral border of the undersides of the wings, the ventral side of the long bones that make up the upper arm and forearm, and the basal part of the lower surface of the interfemoral tail membrane. The coloring of the dorsal area (including the tail membrane) is a mixed brown-gray with a heavy white tinge, giving the bat a frosty appearance. In fact, the bat's name means "frosty or ash colored hairy tail." The individual silky hairs are basally dark, medially yellowish, and distally black with white tips. The belly of the bat is not heavily frosted. The throat has a distinct yellow patch. The hair on the elbow, at the base of the clawed thumb, and the upper arm is yellowish as well. The ears are yellow with black edges. Brownish fur extends out on the underside of the wing nearly to the wrist.

The skull is large (5/8 in. long) and broad (1/2 in. wide), with a large auditory bullae. The bat has large, strong teeth, with the first premolar located at the inner junction of the large canine. Juveniles appear nearly grayish, but still have a frosty appearance.

Food Habits : Moths (Lepidoptera) make up the bulk of the hoary bat's diet. The bat is also known to feed on flies (Diptera), beetles (Coleoptera), small wasps and their relatives (Hymenoptera), grasshoppers, termites, and dragonflies. The bat approaches the insect from behind, taking the abdomen and thorax in its mouth and biting off and swallowing this area of the insect, while dropping the wings and head. In comparison to other bats, the hoary bat feeds on relatively few orders of insects. On rare occasions, the bat has been observed to feed on leaves, grass, shed snake skin, and eastern pipistrelles.

Reproduction: in North America, the hoary bat's breeding range extends across Canada and northcentral and northeastern United States down to at least Kansas and Kentucky, and perhaps to Arkansas, Louisiana, and Georgia. Hoary bats are thought to mate around the time of autumn migration. Researchers are uncertain about whether copulation occurs before, during, or after the southward migration. Courtship is believed to proceed during day flights. Mating may also occur at southern wintering grounds.

Copulation is followed by delayed implantation, a process in which the sperm is stored in the female reproductive track all winter and is available to fertilize the egg when ovulation takes place in the spring. Parturition appears to range from the middle of May into early July. Little is known about the bat's gestation time. One study found three females to deliver between 900 and 1300 hours. Litter size is usually two, but can range from one to four.

Hoary bats give birth to their young while hanging upside down in the leafy shelter of their daytime retreat. The newborn's skin is brown, darker on the body than on the wings, and lighter beneath. The throat and head are much paler and their feet are nearly black. Fine, silver-gray hair covers their dorsal area. The hoary bat's ears and eyes are closed at birth and open on days three and twelve, respectively. Purposeful flight is possible for the infants by the thirty third day. The young cling to the mother in the day, while she sleeps, and hang on a twig or leaf while she hunts at night.

Baker, R. 1983. Michigan Mammals. Michigan State University Press. Lansing, MI. Pgs. 127-132.

Barbour, R. and W. Davis. 1969. The Bats of America. The University of Kentucky Press. Pgs. 143-148

Hoffmeister, D. 1989. Mammals of Illinois. University of Illinois Press. Urbana, Ill. Pgs. 122-125

Kurta, A. 1995. Mammals of the Great Lakes Region. The University of Michigan Press. Ann Arbor, MI. Pgs. 77-79.

Shrump, A. and K. Shrump. 23 Nov. 1982. Mammalian Species. The American Society of Mammalogists. No. 185

Most of  the above information was adapted from: The animal diversity web: http://www.oit.itd.umich.edu/bio108/

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