Vespertilionidaeevening bats and vesper bats

Diversity

Members of family Vespertilionidae, more commonly known as "evening bats" or "vesper bats", form the largest family in order Chiroptera, containing as many as 407 known species, 48 genera, and six subfamilies (Vespertilioninae, Antrozoinae, Myotinae, Miniopterinae, Murininae, and Kerivoulinae). However, this is likely to change in coming years as the family is revised. Vespertilionidae is the second largest mammalian family, surpassed only by family Muridae (Old World rats and mice), which contains over 1,000 species. (Altringham, 1996; Hill and Smith, 1992; Simmons, 2005; Wilson, 1997)

Geographic Range

Vespertilionidae is the most widespread bat family; they are well-established on every continent except Antarctica. They have also managed to colonize many oceanic islands, including Hawaii, Bermuda, the Galapagos, the Azores, Iceland, New Zealand, and possibly Samoa. The only regions of the world they do not inhabit are polar areas, where they are limited by the edge of the tree line, as well as areas with an extremely high elevation. Vespertilioninae, the largest of the six subfamilies, is distributed throughout the family's entire range. Likewise, subfamily Myotinae is found nearly worldwide, although it does not include as many species as subfamily Vespertilioninae, it is the most widely distributed grouping within the family. Subfamilies Miniopterinae, Murininae, and Kerivoulinae are found only in the old world, whereas subfamily Antrozoinae is known from the Nearctic and Neotropical regions. (Arroyo-Cabrales and de Grammont, 2008; Feldhamer, et al., 2007; Hill and Smith, 1992; Miller and Medina, 2008; Slaughter and Walton, 1970; Yalden and Morris, 1975)

The earliest evidence of vespertilionids can be found in European fossil beds, dating back to the Eocene epoch. Other early vespertilionid fossils have been located in Oligocene and Miocene deposits in North America, Pliocene deposits in Asia, and Pleistocene deposits of South America and Africa. Modern vespertilionids have been able to extend their range to temperate areas because of their ability to hibernate during the winter. Many species are capable of adjusting their metabolism and body temperature in order to cope with colder temperatures and lack of food, which has enabled this group to colonize virtually every part of the globe. (Hill and Smith, 1992)

Habitat

Vespertilionids thrive in a wide variety of habitats. They can be found from tropical to temperate areas, and often prefer wooded or open landscapes, depending on the species. Some vespertilionids can even be found in desert habitats. Vespertilionid species are most diverse in tropical regions. Evening bats can roost in a wide variety of places. Many species dwell in dark, enclosed spaces such as caves, mines, tunnels, and human habitations. Other vespertilionids, including painted bats, Welwitsch's bats, American red bats, and hoary bats, roost in trees, where their distinctive color patterns serve as camouflage. Southeast Asian club-footed bats make their homes in hollowed-out bamboo stalks, while rufous mouse-eared bats, whiskered bats, and banana pipistrelles roost in rolled-up leaves. (Altringham, 1996; Hill and Smith, 1992; Koubinova, et al., 2013; Wilson, 1997)

Physical Description

A great deal of morphological diversity exists within this family because it is so large. Most species are relatively small, but can range from 30 to 130 mm and 40 to 80 g. Despite this variation in size, the majority of vespertilionid species have many other physical attributes in common. They are most often characterized by a simple face, lacking a true noseleaf, but these features can be somewhat variable. Their face may also be adorned with a variety of swollen glands and other structures. Their eyes are generally small and hidden by fur. Their external ears are often reduced in size with a simple tragus. Notable exceptions include the genera Plecotus, Idionycteris, and Euderma, which exhibit large ears that become engorged with blood when the bat is active, but subsequently deflate and roll up closer to the head when they are at rest. These long ears can also be fused along their inner edges. Most vespertilionids have drab coloration, usually black, brown, or grey, with a paler underside. However, several arboreal species, particularly painted bats of genus Kerivoula, are known for their striking, high-contrast color patterns that help conceal them as they rest in tree branches. Sexual dimorphism is present in many vespertilionid species. In these cases, the differences in size between the sexes are usually not drastic, but females are always larger than males. This allows females to better maintain homeothermy, put on more body fat, and have access to a wider variety of prey sizes. Bat biologists suspect that this may have evolved in order to compensate for the relatively high cost of pregnancy and lactation. (Altringham, 1996; Hill and Smith, 1992; Myers, 1978; Williams and Findley, 1979; Yalden and Morris, 1975)

  • Sexual Dimorphism
  • female larger

Reproduction

Vespertilionid mating systems may vary widely and are not well known in most species. They typically exhibit polygynous, polygynandrous, and monogamous groupings. As of 2000, only 17 of the over 400 species had well-studied mating systems. Of those, 3 species exhibited year-round harem systems, in which the female population was relatively stable, one species exhibited a similar harem system where the female population was less stable, 6 species exhibited seasonal polygynous groupings, 4 species exhibited seasonal polygynandrous groupings, and 3 species exhibited monogamous behavior. All of the species that mate year-round come from tropical regions of the Old World. Most of the species that mate seasonally are found in either subtropical or temperate regions. The ways in which vespertilionids find, attract, and defend mates is extremely varied, so it is difficult to list all of them. In general, mating is non-random, and males in harem-forming species (such as Myotis bocagii) attempt to defend females against other males. Some species, such as little brown bats, may use specialized vocalizations to attract females. (Crichton and Krutzsch, 2000; Feldhamer, et al., 2007; Fenton, 2001; Nowak, 1999; Wilson, 1997)

The breeding habits of vespertilionid bats are somewhat variable. They can be monestrous or polyestrous, although the polyestrous condition is more common in tropical species. In most temperate and some tropical species, females exhibit delayed fertilization and store sperm from fall matings throughout the winter during hibernation, sometimes mating again in the spring. For example, female Townsend's big-eared bats undergo estrus in August and copulate in late fall throughout the winter. The egg is fully developed and remains enclosed in the follicle, so it cannot be fertilized while she hibernates. Sperm remains alive within the female's reproductive tract during this time, nourished by a special epithelium on the walls of her uterus. This allows the sperm to keep for quite some time; female common pipistrelles are able to maintain sperm in their uteri for up to seven months. Males are also able to store sperm in their epididymis for a similar period of time and still produce healthy pups. Some species, such as common bent-winged bats, experience delayed implantation, in which the egg is fertilized immediately after copulation, undergoes a few divisions, and then becomes inactive. When the female awakens from hibernation and levels of LH and progesterone increase, the blastocyst implants and the placenta develops. Vespertilionidae is the only bat family that ever has litters of three or more young and it is one of only four bat families that commonly have more than one offspring per breeding season. Gestation is typically 40 to 70 days, but can take much longer in species where development can be delayed due to environmental factors. (Nowak, 1999; Schober, 1984; Wilson, 1997; Yalden and Morris, 1975)

As with all placental mammals, female vespertilionid bats nourish their young through a placenta during gestation. After birth, young vespertilionids receive parental care exclusively from their mothers, who provide milk for the first few weeks of their lives. Females invest heavily in their offspring. For example, female common pipstrelles usually only give birth to a single pup (or more rarely, twins), and nurse them for up to four weeks after giving birth. Young bats may also receive non-nutritional care from their mothers. Studies have shown infants of little brown bats need adults crowded around them to maintain their body temperature. This has lead some species to form brooding colonies. Young vespertilionids may also learn certain behaviors from their mothers. Young bats may also alter their feeding behavior based on the sounds they hear adults make while chewing. Female bats may "adopt" other young if their own offspring die. In colonial species, females keep track of which young they are nursing through a combination of echolocation and smell. After they begin nursing particular young, they will not switch. No significant maternal care occurs after weaning in most species, once they learn to fly and forage on their own, young bats are essentially independent. However, studies on European bats have indicated offspring/parent associations may continue after this point. (Altringham, 1996; Crichton and Krutzsch, 2000; Fenton, 2001; Nowak, 1999; Racey and Swift, 1995; Wilson, 1997)

Lifespan/Longevity

Vespertilionid bats typically only live about 4 to 6 years in the wild, but some live considerably longer, for instance, some Myotis species live well past twenty years. Captive individuals more commonly reach the two-decade mark. (Altringham, 1996; Nowak, 1999)

Behavior

Bats from this group exhibit a wide range of behaviors. Like all bats, they fly, and are active primarily at night, roosting in a variety of places during the day. Tropical species tend to stay in the same general areas year round, but temperate species, such as genus Lasiurus may migrate. However, winter hibernation is more common than migration among temperate species. Species such as little brown and big brown bats often hibernate underground or in caves during the coldest months. Sociality ranges from completely solitary species, such as eastern red bats, to colonial species that roost together in large numbers, often in caves, such as cave myotis. In colonial species, social hierarchies may exist among adults. In some species, females form brooding colonies together while adult males live separately; this behavior had been seen in some Myotis populations. (Altringham, 1996; Schober, 1984; Simmons and Conway, 1997; Yalden and Morris, 1975)

Communication and Perception

Like all bats, vespertilionids use a "multi-modal" method of communication and perception. Hearing, sight, and olfaction are all important components of their sensory adaptations. Hearing is particularly important since, like many other bats, vespertilionids utilize ultrasonic echolocation to locate prey. They emit high frequency vibrations and are able to detect potential prey based on the sounds that bounce back, using this information to create a mental picture of their environment. All vespertilionids use pulses that vary in frequency as they are produced, which is why they are classified as frequency modulating bats. Although most species hear fairly well from 10 to 50 kHz, many species are best adapted for the particular frequency range they use to detect and track prey. This varies between species. Big brown bats for example, are sensitive to frequencies at about 60 kHz, while little brown bats are sensitive to frequencies at about 40 kHz. Hearing is also important for communication with conspecifics, many of which emit "social calls" apart from echolocation calls. Social calls are typically below the frequency used in echolocation and are often audible to humans. This type of communication may be especially important for mothers to stay in contact with their young. In contrast, visual perception plays a much less significant role in their ability to detect objects at a close range. Vision is probably most important for the detection of objects that echolocation cannot precisely detect, such as objects that are far away. Big brown bats, for example, can visually detect large objects as far as 300 m away, however, using echolocation alone, they may not detect it until it is less than 40 m away. Desert long-eared bats likely use visual perception as a means of foraging. For most vespertilionids, visual cues are likely most important in non-predatory activity, such as determining when to return and when to leave day roosts, or in navigating back to roosts. Olfaction is primarily important as a means of perceiving conspecific signals. Females may use odors to find their pups them within a colony. Adults may use scent as a means of distinguishing between one another and in finding their roosting sites. Additionally, little brown bats place scent marks near new roosts. (Fenton, 2001; Harris, 1999; Kunz and Fenton, 2003; Nowak, 1999; Popper and Fay, 1995; Simmons and Conway, 1997; Wilson, 1997; Yalden and Morris, 1975)

Food Habits

Vespertilionids feed primarily on insects and other small arthropods. However, some species, such as pallid bats of the American southwest, hunt scorpions and other larger prey. Evening bats are famous for their ability to acrobatically capture prey in mid-air, using their wings to flip the item into their tail membranes. They duck their heads underneath their bodies to retrieve food items with their mouths, which often takes the form of an aerial somersault. They also pick stationary prey directly from the ground, or off leaves. Vespertilionid foraging is not restricted to over land, it can also occur over water. Some species, belonging to genus Myotis, such as fish-eating bats from the Gulf of California, are known to prey on shrimp and small, sea-faring fish. Vespertilionids generally prefer to hunt in open spaces, but can forage in dense vegetation if necessary. They are often territorial and vigorously defend their foraging areas from other bats. (Altringham, 1996; Hill and Smith, 1992; Neuweiler, 2000; Nowak, 1999; Wilson, 1997)

Predation

Birds, snakes, and other arboreal animals including other bat varieties are known to prey on vespertilionids. Evening bats enter a torpid state during the day, which makes them particularly vulnerable to predation. However, in higher risk locations, bats tend to roost in spaces that are too tight for predators, such as hollowed out tree trunks. (Kunz and Fenton, 2003; Slaughter and Walton, 1970)

Ecosystem Roles

Most vespertilionids are voracious insect predators. They devour hundreds of insects nightly; this is especially true of temperate species during the summer and females during peak lactation. It has been estimated that individual adult bats in Kansas can eat about 2.0 g of insects daily. This puts their annual insect consumption at more than 16 tons each year. Vespertilionids host many ectoparasites such as mites, fleas, and ticks. (Kunz and Fenton, 2003; Kunz, 1974; Kunz, et al., 1998; Kurta, et al., 1989; Wilson, 1997)

Commensal/Parasitic Species

Economic Importance for Humans: Positive

Vespertilionids consume insects that can serve as vectors for human illnesses. They also help control agricultural, garden and ornamental plant pests, preying on harmful insects. (Agosta and Morton, 2003)

  • Positive Impacts
  • controls pest population

Economic Importance for Humans: Negative

The rabies virus can be carried by some vespertilionid species, although it is not carried by all species. Correlations between species and their ability to carry rabies are not known. Families Pteropodidae, Molossidae and Phyllostomidae along with Vespertilionids, have all tested positive for the rabies virus. (Constantine, 1988; Wilson, 1997; Wong, et al., 2006)

  • Negative Impacts
  • injures humans
    • carries human disease

Conservation Status

In 2008, the IUCN reported 44 vespertilionid species were in danger of extinction, from nearly every part of the world, from the tropics to temperate zones. Of these, 7 are critically endangered, 17 are endangered, and 20 are vulnerable. The IUCN expects to add at least 30 more species to these categories in the near future. The largest percentage comes from genus Myotis; this may be merely due to the fact that they are the largest vespertilionid genus. Conservation biologists are also particularly concerned about Thomas's big-eared bats, which are critically endangered and are the only extant representatives of their genus (Pharotis). The six other critically endangered vespertilionid species are gloomy tube-nosed bats, Armenian whiskered bats, Yanbaru whiskered bats, Lord Howe long-eared bats, New Caledonia long-eared bats, and Christmas Island pipistrelles. ("IUCN", 2008)

Habitat destruction is one of the biggest threats to bats worldwide, caused by deforestation due to logging, agriculture, infrastructure development for human settlements, and fire. All of the aforementioned activities destroy roosting sites for arboreal species. Cave dwelling vespertilionids are also in danger, especially species such as Indiana bats that hibernate in one particular location in large numbers. In these cases, an entire species can be decimated if even one cave is disturbed. ("IUCN", 2008; "Bat Conservation Topics", 2009)

Some vespertilionids have experienced unusually high mortality due to the increasing number of wind turbines erected in recent years. According to a 2005 study of two wind farms in Pennsylvania and West Virginia, 1,700 and 2,100 bat fatalities were reported within a six week period, respectively. According to the Bats and Wind Energy Cooperative (BWEC), several measures are currently being pursued to ensure minimal bat fatalities as a result of wind farms, including assessing bat activity before constructing turbines, monitoring and comparing mortality at existing facilities to detect patterns related to environmental variables, and finding ways to keep bats from coming into contact with turbines. ("Bats and Wind Energy Cooperative (BWEC)", 2008)

Another emerging threat to vespertilionids is disease. White-nose syndrome is a poorly-understood but deadly condition that is characterized by fungal growth on the muzzle, ears, and wing membranes, which is possibly an opportunistic infection. First discovered during the winter of 2006 to 2007 in caves in New York, it has killed over a half million hibernating vespertilionids in Eastern North America, including little brown bats, big brown bats, small-footed myotis, northern long-eared myotis, eastern pipistrelles, and Indiana bats. This phenomenon is unprecedented, and the causes of this epidemic are currently unknown. The US Fish & Wildlife Service (USFWS) has confirmed cases of WNS in New York, Vermont, Connecticut and Massachusetts, and expects additional fatalities in adjacent states in the future, including New Hampshire, Rhode Island, New Jersey and Pennsylvania. In March 2009, the USFWS restricted spelunking in these states to prevent the spread of WNS. Many conservation groups and governmental organizations, as well as the scientific community have launched research projects to better understand the causes and the high mortality rates associated with WNS. ("US Fish & Wild Service", 2009; "White Nose Syndrome", 2009; Cohn, 2008)

  • IUCN Red List [Link]
    Not Evaluated

Contributors

Katherine Merrill Birkett (author), University of Michigan-Ann Arbor, Kayla Shaun Weidman (author), University of Michigan-Ann Arbor, Yangshin Woo (author), University of Michigan-Ann Arbor, Phil Myers (editor, instructor), University of Michigan-Ann Arbor, Leila Siciliano Martina (editor), Animal Diversity Web Staff.

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

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Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

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Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

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Neotropical

living in the southern part of the New World. In other words, Central and South America.

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Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

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acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

arboreal

Referring to an animal that lives in trees; tree-climbing.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

bog

a wetland area rich in accumulated plant material and with acidic soils surrounding a body of open water. Bogs have a flora dominated by sedges, heaths, and sphagnum.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

colonial

used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.

cosmopolitan

having a worldwide distribution. Found on all continents (except maybe Antarctica) and in all biogeographic provinces; or in all the major oceans (Atlantic, Indian, and Pacific.

delayed fertilization

a substantial delay (longer than the minimum time required for sperm to travel to the egg) takes place between copulation and fertilization, used to describe female sperm storage.

delayed implantation

in mammals, a condition in which a fertilized egg reaches the uterus but delays its implantation in the uterine lining, sometimes for several months.

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

dominance hierarchies

ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates

echolocation

The process by which an animal locates itself with respect to other animals and objects by emitting sound waves and sensing the pattern of the reflected sound waves.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

hibernation

the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.

insectivore

An animal that eats mainly insects or spiders.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

marsh

marshes are wetland areas often dominated by grasses and reeds.

migratory

makes seasonal movements between breeding and wintering grounds

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oceanic islands

islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

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pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

piscivore

an animal that mainly eats fish

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

polygynous

having more than one female as a mate at one time

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

scrub forest

scrub forests develop in areas that experience dry seasons.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

sperm-storing

mature spermatozoa are stored by females following copulation. Male sperm storage also occurs, as sperm are retained in the male epididymes (in mammals) for a period that can, in some cases, extend over several weeks or more, but here we use the term to refer only to sperm storage by females.

stores or caches food

places a food item in a special place to be eaten later. Also called "hoarding"

suburban

living in residential areas on the outskirts of large cities or towns.

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

ultrasound

uses sound above the range of human hearing for either navigation or communication or both

urban

living in cities and large towns, landscapes dominated by human structures and activity.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

year-round breeding

breeding takes place throughout the year

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