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Overview

Brief Summary

Bats are the only mammals that can really fly. They are very mysterious animals, appearing only after twilight to hunt insects. Even with the best of eyes, these small insects are not visible in the dark. That is why bats have such good ears. To 'see', bats transmit signals which return as echos when they bounce against something, such as an insect. They receive these echos with their ears. This method is called echolocation.
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Introduction

The clade Chiroptera includes two extant clades, Megachiroptera (Old World Fruit Bats) and Microchiroptera (echolocating bats). In addition, Chiroptera includes at least four extinct clades that are most closely related to Microchiroptera. There are over nine hundred extant species of bats (Koopman, 1993). Bats vary greatly in size. The smallest bat, Craseonycteris thonglongyai (Microchiroptera), weighs less than 2 g and has a wingspan of 12-13 cm, while the largest bats, those of the genus Pteropus (Megachiroptera), weigh up to 1.5 kg and may have a wing span over 2m (Fenton, 1992).

Bats are unique among mammals as they are the only group to have evolved true powered flight. Some other mammals such as "flying" squirrels and "flying" lemurs can glide through the air for long distances, but they are not capable of sustained flight. In contrast, bats can propel themselves with their wings, gaining and loosing altitude and flying for long periods.

Bats are nocturnal and usually spend the daylight hours roosting in caves, rock crevices, trees, or manmade structures such as houses and/or bridges. Some bats are solitary, while others are found in colonies that may include over a million individuals.

Activity begins around dusk, when bats leave the day roost and start feeding. The clade Chiroptera includes species with very diverse food preferences, including bats that eat either meat, insects, fish, fruit, nectar, or a variety of food types. Only three species of bats actually feed on blood Desmodontinae). Many bats remain at their feeding sites until just before dawn when they return to the day roost.

Classification outlines the higher-level classifications within Chiroptera.

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Comprehensive Description

Diversity

Bats are the second-most speciose group of mammals, after rodents. The approximately 925 species of living bats make up around 20% of all known living mammal species. In some tropical areas, there are more species of bats than of all other kinds of mammals combined.

Bats are often divided into two major groups, usually given the rank of suborders, Megachiroptera and Microchiroptera. Although these groups probably do not represent monophyletic lineages (discussed in more detail below), there are several relevant ecological differences between them. These groups will be used throughout this account in describing the diversity of bat life histories.

Megachiroptera includes one family (Pteropodidae) and about 166 species. All feed primarily on plant material, either fruit, nectar or pollen. The remaining 16 families (around 759 species) belong to Microchiroptera. The majority of species are insectivorous, and insectivory is widely distributed through all microchiropteran families. However, many microchiropterans have become specialized to eat other kinds of diets. Some bats are carnivorous (feeding on rodents, other bats, reptiles, birds, amphibians, and even fish), many consume fruit, some are specialized for extracting nectar from flowers, and one subfamily (three species in the subfamily Desmodontinae) feeds on nothing but the blood of other vertebrates. Megachiropterans and microchiropterans differ in many other ways. Megachiropterans are found only in the Old World tropics, while microchiropterans are much more broadly distributed. Microchiropterans use highly sophisticated echolocation for orientation; megachiropterans orient primarily using their eyes, although members of one genus, Rousettus, are capable of a simple form of echolocation that is not related to echolocation in microchiropterans. Megachiropteran species control their body temperature within a tight range of temperatures and none hibernates; many microchiropterans have labile body temperatures, and some hibernate.

  • Hill, J., J. Smith. 1984. Bats: A Natural History. Austin: University of Texas Press.
  • Vaughan, T., J. Ryan, N. Czaplewski. 2000. Mammalogy, 4th Edition. Toronto: Brooks Cole.
  • Van den Bussche, R., S. Hoofer. 2004. Phylogenetic relationships among recent chiropteran families and the importance of choosing appropriate out-group taxa. Journal of Mammalogy, 85: 321-330.
  • Teeling, E., M. Springer, O. Madsen, P. Bates, S. O'Brien, W. Murphy. 2005. A molecular phylogeny for bats illuminates biogeography and the fossil record. Science, 307: 580-584.
  • Teeling, E., O. Madsen, R. van den Bussche, W. Jong, M. Stanhope, M. Springer. 2002. Microbat monophyly and the convergent evolution of a key innovation in old world rhinolophoid microbats. Proceedings of the National Academy of Sciences of the United States of America, 99: 1431-1436.
  • Nowak, R. 1991. Order Chiroptera. Pp. 190-194 in Walker's Mammals of the World, Vol. 1, 5th Edition. Baltimore: Johns Hopkins University Press.
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Bat Monophyly

Until the 1970s, most evolutionary biologists assumed that bats form a monophyletic group. Recently, however, several authors have questioned monophyly of Chiroptera (Jones and Genoways, 1970; Smith, 1976, 1980; Smith and Madkour, 1980; Hill and Smith, 1984; Pettigrew, 1986, 1991a, 1991b; Pettigrew and Jamieson, 1987; Pettigrew et al., 1989) creating what has become known as the “bat monophyly controversy”. Proponents of the hypothesis that bats are diphyletic pointed out that many similarities between Megachiroptera and Microchiroptera involve the flight mechanism. It is therefore possible that convergent evolution of aerial locomotion, rather than shared ancestry, might account for the similarities found between megachiropteran and microchiropteran bats (Jones and Genoways, 1970).

The bat monophyly hypothesis states the Megachiroptera and Microchiroptera are each others closest relatives in an evolutionary sense (i.e., they form a clade). If this is true, then their shared characteristics, including the ability to fly, would have been present in their most recent common ancestor (Simmons, 1994; 1995). It follows from this that there was only one origin of powered flight in mammals. In contrast, the diphyly hypothesis states that megachiropteran and microchiropteran bats do not form a monophyletic group, instead having evolved independently from two different groups of non-flying mammals. It has been suggested that Megachiroptera is more closely related to Dermoptera and Primates than to Microchiroptera (Smith and Madkour, 1980; Pettigrew, 1986, 1991a, b, 1995; Pettigrew and Jamieson, 1987; Pettigrew et. al., 1989). In this case, the characteristics common to both groups of bats either evolved as a result of convergent evolution or are simply the result of retention of primitive features. If bats are diphyletic, the ability to fly must have evolved once in Megachiroptera and again in Microchiroptera.

There have been numerous studies using biochemical, molecular, and/or morphological data to analyze the relationship between Megachiroptera, Microchiroptera and other taxa. Diphyly has only been supported in two data sets: features of the nervous system (Pettigrew, 1986, 1991a, 1991b; Pettigrew et. al., 1989; Johnson and Kirsch, 1993) and of the penis (Smith and Madkour, 1980). In contrast, monophyly has been supported in studies examining a large and diverse set of morphological features, including those of the nervous and reproductive systems (Luckett, 1980a, 1993; Wible and Novacek, 1988; Kovtun, 1989; Thewissen and Babcock, 1991, 1993; Kay et. al., 1992; Novacek, 1992, 1994; Beard, 1993; Simmons, 1993a, 1994, 1995; Wible and Martin, 1993; Simmons and Quinn, 1994, Miyamoto, 1996), DNA-DNA hybridization data (Kirsch et al., 1995; Hutcheon and Kirsch, 1996; Kirsch, 1996), and DNA nucleotide sequence data from mitochondrial and nuclear genes (Adkins and Honeycutt, 1991, 1993, 1994; Mindell et al., 1991; Ammerman and Hillis, 1992; Bailey at al., 1992; Stanhope et al., 1992, 1993, 1996; Honeycutt and Adkins, 1993; Knight and Mindell, 1993; Novacek, 1994, Allard et al., 1996; Miyamoto, 1996; Porter et al., 1996).

Because the vast majority of available data strongly support a sister-group relationship between Megachiroptera and Microchiroptera, bat monophyly is now regarded as a very strongly supported hypothesis.

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Characteristics

Unique Characteristics

One unique feature of bats is their modified forelimbs, which support a wing membrane (patagium). The basic elements of the mammalian limb are present in bats, although the relative sizes of most bones and muscles differ from those of nonflying mammals. The most elongated parts of the limb are those of the hand (metacarpal bones) and fingers (phalanges). The primary functions of these bones in bats is to provide support for the patagium and control its movements. The patagium stretches between the fingers and attaches to the side or back of the bat and the lower leg. Part of the membrane extends between the hindlimbs. Numerous blood vessels and nerves are present throughout the wing membrane. Bats also have five unique muscles present in the patagium, and use additional muscles in the chest and back to move the wings up and down.

The most obvious difference between bird wings and those of bats is that bird wings are made of feathers, not a skin membrane. Birds have an elongated arm, but do not have elongated fingers like bats. Additionally, the muscles used in both the upstroke and downstroke are found in the chest of birds, while the upstroke muscles are on the back in bats (Fenton, 1983).

The orientation of the hindlimb is also unique to bats. The hip joint is rotated 90° so that the legs project sideways and the knee faces almost backwards. Due in part to the rotation of the hindlimb, the walking motion of bats differs from other tetrapods, often appearing awkward. The hindlimb is designed to support the patagium in flight and allow the bat to roost hanging from its hindlimbs. Most bats have a tendon system in the toes that locks the claws in place so the bat can hang upside down even when asleep.

Bats have other unique characteristics including many morphological synapomorphies.

General Characteristics

The body of a bat is ventrally compressed with a short neck region. The bones tend to be slender and light-weight. The majority of the body weight is concentrated in the chest region due to the large flight muscles.

The overall shape of the head varies more in bats than within most other groups of mammals. Some bats have very elongated muzzles while others have broad, short faces. There is a correlation between the shape of the head and the type of food eaten. For example, most nectar feeders have long, narrow muzzles that are good for reaching into flowers, while many fruit eaters have short, broad faces good for biting rounded fruits (Hill and Smith, 1984).

The ears range from small and round to large and pointed, and often have a cartilaginous fold (tragus) present at the notch of the ear. There is additional variation in the nasal and lip regions of bats. Some bats have complex noseleafs, folds, or wrinkles on their muzzles. The function of facial ornamentation is not well understood, although it may effect the emission of echolocation calls in some taxa (Fenton, 1992).

A major misconception about bats is that they are blind. This idea originated from the fact that bats are able to successfully maneuver in the dark and often have small eyes. While some bats do have very small eyes (most Microchiroptera) many have large and complex eyes (Megachiroptera). Experiments on several species of bats have shown that they are able to distinguish patterns even at low light levels (Hill and Smith, 1984).

Bats usually have black or brown fur, although the fur can also be gray, white, red, or orange. In some species there are stripes on the face or down the back, or patches of white on the face or above the shoulder. The length of the fur also varies among species from short and dense to long and fluffy. The wing membrane is usually dark in color, although it may have white on the tips or be a lighter color around the bones in the membrane. A few bats have white or pale yellow wings. There are also little hairs on the membrane itself. These hairs can be the color of the wing or the same color as the body.

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Distribution

Geographic Range

Bats are found throughout the world in tropical and temperate habitats. They are missing only from polar regions and from some isolated islands. Although bats are relatively common in temperate regions, they reach their greatest diversity in tropical forests.

Biogeographic Regions: nearctic (Native ); palearctic (Native ); oriental (Native ); ethiopian (Native ); neotropical (Native ); australian (Native ); oceanic islands (Native )

Other Geographic Terms: cosmopolitan ; island endemic

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Geographic Distribution


The geographical distribution of bats is shown in red. Distribution from Hill and Smith (1984).

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Physical Description

Morphology

Physical Description

Bats are unmistakable. No mammals other than bats have true wings and flight.   Bat wings are modified forelimbs, much as are bird wings, except in the case of bats the flight surface is covered with skin and supported by four fingers, while in birds the flight surface is provided mostly by feathers and is supported by the wrist and two digits. The flight membrane usually extends down the sides of the body and attaches to the hind legs. Bats also often have a tail membrane called a uropatagium. In order to accomodate powerful flight muscles, the thoracic region of bats is quite robust. In addition to providing power, a massive chest and shoulders maintains the center of gravity between the wings, making flight more efficient. The opposite is true of the posterior end of the body, which is small relative to the chest and back. The hindlimbs in particular are generally short and small, with sharp, curved claws that help bats cling to surfaces in their roost.

An important cranial characteristic for recognizing bat families is the nature of the   premaxilla.

The suborder names, Megachiroptera and Microchiroptera, imply that megabats are all large and microbats are all small, which is is not always the case. The smallest bat is indeed a microchiropteran (Craseonycteris thonglongyai) and weighs only 2 to 3 grams. Likewise, the largest bats are among the Megachiroptera and can weigh up to 1500 grams. Size varies with each group, however, with the smallest megachiropterans weighing only 13 grams and the largest microchiropterans weighing nearly 200 grams.

There are several obvious morphological features that distinguish the two suborders. Megachiropterans rely on vision to orient in the dark of night, and thus have large, prominent eyes. All microchiropterans rely heavily on echolocation, and not vision, and generally have small eyes. Instead most microchiropterans have large, complex pinnae (external ears), including an enlarged tragus or antitragus. Megabats have claws on the second digits supporting their wings (with one exception); this is never the case in microbats. Microbats often have dentition or cheek teeth whose morphology can easily be related to   dilambdodont teeth; megabats have simplified cheek teeth that are difficult to interpret.

Other Physical Features: endothermic ; heterothermic ; homoiothermic; bilateral symmetry

Sexual Dimorphism: sexes alike; female larger; sexes shaped differently

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Ecology

Habitat

Bats can be found in many terrestrial habitats below the polar regions. Typical habitats include temperate and tropical forests, deserts, open fields, agricultural areas, and in suburban and urban environments. Many bats forage near freshwater streams, lakes and ponds, preying on insects as they emerge from the water. Generally, if a terrestrial habitat provides access to sufficient roost sites and appropriate food, one or more species will be found there. Bats generally have very specific roosting requirements, which differ among species. They may roost in caves, crevices, trees, under logs, and even in human dwellings. Bats may also use different types of roosts at different times. For example, a species that hibernates in a cave during the winter may use crevices in tree holes as roosts during warmer months.

Habitat Regions: temperate ; tropical ; terrestrial

Terrestrial Biomes: desert or dune ; savanna or grassland ; chaparral ; forest ; rainforest ; scrub forest ; mountains

Wetlands: marsh ; swamp ; bog

Other Habitat Features: urban ; suburban ; agricultural ; riparian ; estuarine

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Trophic Strategy

Food Habits

As a group, bats eat a wide variety of food types. The majority of species eat insects, either taking them on the wing or picking them off of surfaces. Species specialized for eating fruit, nectar, or pollen are especially abundant and diverse in tropical regions. Some bats eat vertebrates like frogs, rodents, birds, or other bats. Several species (e.g., Noctilio leporinus and Myotis vivesi) are specialized to trawl for fish. Three species of bats, the vampire bats subsist solely on the blood of other vertebrates. Although most stories related to mythical "vampires" originated in the Old World, there are no Old World bat species that feed on blood. Vampire bats occur only in the neotropics. Vampire bats eat blood by using their sharp incisors to make incisions in the skin of their their prey. An anticoagulant in their saliva keeps blood flowing while they lap it up. Only one of these three species eats the blood of mammalian prey, the common vampire bat (Desmodus rotundus). The other two species (Diaemus youngi and Diphylla ecaudata) are specialized for feeding only on birds. Although most bats tend to be specialized for a particular diet, most frugivorous bats also include arthropod prey in their diet when available. At least one extant species, the unusual New Zealand lesser short-tailed bat (Mystacina tuberculata), is omnivorous.

The different food preferences of bats are widely distributed among families. Megachiropterans eat only fruit and nectar, but the entire range of diets can be found among microchiropterans. Insectivory is common in many families, and carnivory on vertebrates is exhibited by several. The New World leaf-nosed bats (family Phyllostomidae) in particular have undergone an extensive radiation in ecology and food habits. The entire range of diets exploited by all of Chiroptera can be observed in this single family, which also includes the only sanguivorous (blood feeding) bats.

Primary Diet: carnivore (Eats terrestrial vertebrates, Piscivore , Sanguivore , Insectivore , Eats non-insect arthropods); herbivore (Frugivore , Nectarivore ); omnivore

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Associations

Animal / dung saprobe
sporangiophore of Coemansia erecta is saprobic in/on dung or excretions of dung of Chiroptera

Animal / associate
larva of Fannia canicularis is associated with nest of Chiroptera

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Ecosystem Roles

Because of their high metabolic needs and diverse diets, bats can impact the communities in which they live in a variety of important ways. They are important pollinators and seed dispersers, particularly in tropical communities. Also, carnivorous and insectivorous bats may significantly limit their prey populations. Bats may be keystone species in many communities, particularly in the tropics where they are most abundant and diverse.

Bats are associated with many kinds of internal and external parasites. They are known to harbor several protozoans that cause malaria (e.g., Plasmodium, Hepatocystis, Nycteria and Polychromophilus) although none of the malarial parasites found in bats cause malaria in humans. Trypanosome protozoans, that may cause a variety of diseases, such as sleeping sickness, are also found in a number of bat species. Many flatworms (Cestoda and Trematoda) and roundworms (Nematoda) spend at least part of their life cycle within the tissues of bat hosts. Bats commonly harbor external, arthropod parasites. Ticks, mites and insects such as true bugs and fleas are known to live and feed on bats. An entire family of flies, Streblidae, has co-evolved with bats. These flies have secondarily lost the ability to fly, living only in the fur of bats. Species that parasitize bats exhibit a range of host-specificity: some are found on one or a few bats, others occur on a wider variety of bat species, and still others can parasitize bats as well as other taxonomic groups.

Ecosystem Impact: disperses seeds; pollinates; keystone species

Commensal/Parasitic Species:

  • Jones, K., A. Purvis, J. Gittleman. 2003. Biological correlates of extinction risk in bats. American Naturalist, 161: 601-614.
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Predation

Few studies have directly examined the effects of predators on bat populations. Most of this type of information comes from anecdotal observation of predation events or evidence of bats in the scat of predators. Groups that are known to eat bats are owls and other birds of prey, many carnivores, other bats, and snakes.

Bats are probably most vulnerable to predators as they roost during the day or emerge in large groups in the early evening. Predators like snakes or hawks often wait near the entrances of caves at dusk, attacking bats as they leave the roost. Juvenile bats that cannot yet fly are also at risk of predation if they fall to the ground. Individual bats flying in the dark of night are probably difficult to catch, even for owls, which can fly and locate prey well in the dark. Several species of bat have become specialized for preying on other bats, these include the New World species Vampyrum spectrum and Chrotopterus auritus, and two Old World species in the genus Megaderma.

Bats generally avoid predation by staying in protected roosts during the day and through agile flight at night. Most bats are also cryptically colored.

Known Predators:

  • owls
  • hawks
  • bats
  • Mammalian carnivores
  • snakes

Anti-predator Adaptations: cryptic

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Known prey organisms

  • H. W. Koepcke and M. Koepcke, Sobre el proceso de transformacion de la materia organica en las playas arenosas marinas del Peru. Publ. Univ. Nac. Mayer San Marcos, Zoologie Serie A, No. 8, from p. 24 (1952).
  • E. Percival and H. Whitehead, 1929. A quantitative study of the fauna of some types of stream-bed. J. Ecol. 17:282-314, from p. 311 & overleaf.
  • J. L. Harrison, The distribution of feeding habits among animals in a tropical rain forest, J. Anim. Ecol. 31:53-63, from p. 61 (1962).
  • Myers, P., R. Espinosa, C. S. Parr, T. Jones, G. S. Hammond, and T. A. Dewey. 2006. The Animal Diversity Web (online). Accessed February 16, 2011 at http://animaldiversity.org. http://www.animaldiversity.org
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Life History and Behavior

Behavior

Communication and Perception

Echolocation is another signature life history strategy in bats. All microchiropterans rely heavily on echolocation to navigate through their environment and to find food. Bats call at frequencies that are typically higher than humans can hear. These sounds bounce off objects and produce echoes, which bats can hear and interpret. Bat calls vary in duration and structure. Some species use short calls (2 to 5 milliseconds) at a high rate of repetition, while other species use longer (about 20 milliseconds), but less frequent calls. The frequency (pitch) characteristics also vary within and among species. Differences in characteristics like frequency and duration affect the ability of an echolocation call to produce echoes from objects of different sizes, shapes, and at different distances. As a result, echolocation call structure can reveal quite a bit about the ecology and foraging strategy of a bat species.

Perhaps the biggest functional difference between vision and echolocation is that vision is a passive mode of perception, while echolocation is an active mode of perception. Vision typically relies on external sources of light energy. Echolocation is quite different in that the energy provided is by the animals themselves. Because bats have tight control over what kinds of sound they produce, bats can exhibit a high degree of control over what types of objects they can perceive. Echolocation calls vary among species, within species, and even within individuals. This variation in echolocation behavior reflects variation in the habitats bats are using and the food for which they are searching. Bats can also use "passive echolocation", detecting and locating prey based on prey-generated sounds, such as frogs calling or the sound of a beetle walking across sand.

Bats communicate with one another in a variety of ways. Although bats may be able to hear and interpret the echolocation calls of other bats, there is little evidence that those calls are used directly in communication. Bats employ a suite of communication calls, most of which are audible to the human ear. Some species use a diverse repertoire of social calls, which can be useful in intra-specific agression, mother-infant communication, and mating behavior.

Scent marks and pheromones are also important in bats, as they are in other mammals. Scent is used to communicate reproductive status and individual or group identity. Many species have special scent glands near their faces or their wings. One family, the sac winged bats (Emballonuridae), are so called because of a sac on the leading edge of their wing that may be a scent gland.

Bats also communicate with visual displays, often during courtship. Some species have special markings on their wings or pelage, and engage in ritualized displays to attract mates.

Communication Channels: visual ; tactile ; acoustic ; chemical

Other Communication Modes: pheromones ; scent marks

Perception Channels: visual ; acoustic ; ultrasound ; echolocation

  • Behr, O., O. von Helversen. 2004. Bat serenades--complex courtship songs of the sac-winged bat (Saccopteryx bilineata). Behavioral Ecology and Sociobiology, 56: 106-115.
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Life Expectancy

Lifespan/Longevity

Bats live surprisingly long lives. Typically, mammalian lifespans roughly correlate with their body size: smaller mammals live short lives, whereas larger mammals live longer lives. Bats are the only group of mammals that does not conform to this relationship. Despite the fact that bats are generally small mammals, many bats can live over 30 years in the wild. Where data on longevity is available, lifespans in the wild are often recorded from 10 to 25 years. Typically, a given species will live at least 3.5 times longer than other mammals of similar size.

There are several viable hypotheses to explain longevity in bats. Hibernation and daily torpor may restrict lifetime energy expenditure in individuals, allowing them to live longer. Lack of predation pressure on adults may also allow bats to live long lives. For their size, bats have low reproductive rates in a given breeding season. Typically, females give birth to only one or two young per year, but reproduce many times over a long life. By evolving a reproductive strategy that is more typical of large mammals, perhaps lifespans have evolved to match those of large mammals as well.

The longest-lived bat on record is a little brown bat (Myotis lucifigus). One banded individual was recaptured 33 years after it was originally tagged. These bats weigh only 7 grams as adults, roughly 1/3 the size of a house mouse. Myotis lucifugus is one of the most widely studied species worldwide; thus, it would not be surprising if other, less well-known species live even longer.

  • Kurta, A. 1995. Mammals of the Great Lakes Region. Ann Arbor: University of Michigan Press.
  • Wilkinson, G., J. South. 2002. Life history, ecology and longevity in bats. Aging Cell, 1: 124-131.
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Reproduction

Mating systems vary among bat species. Many temperate bats mate in the fall as they aggregate near their winter hibernacula. These bats are generally promiscuous. Pteropodids also tend to have promiscuous mating systems. These bats often aggregate in large groups in one or a few trees and mate with various nearby individuals. In many neotropical microchiropterans, one or two males defend small harems of females. Males secure all matings with their harem females until other males supplant them. While most species are either polygynous or promiscuous, there are some bats that are monogamous. In these cases, the male, female, and their offspring roost together in a family group and males may contribute to protecting and feeding the young. Examples include Vampyrum spectrum, Lavia frons, Hipposideros galeritus, H. beatus, Nycteris hispida, N. arge, N. nana, and some Kerivoula species. One megachiropteran species, Hypsignathus monstrosus, has a lek mating system, where males gather in a lekking arena to display to females, who then choose the most desirable of mates. Courtship behavior is complex in some species, while in others, it can be nearly nonexistent (e.g., males of some species will mate with hibernating females that barely react to the copulation event).

Mating System: monogamous ; polygynous ; polygynandrous (promiscuous)

A large number of bats breed seasonally. Temperate species often breed before they enter hibernation while many tropical species breed in a cycle that is linked to wet-dry seasonality. All species that are not seasonal breeders occur in the tropics, where resources may not be as variable as in temperate regions. The function of seasonal breeding is to coordinate reproduction with the availability of resources to support newborn young. To this end, many species have also evolved complex reproductive physiology including delayed ovulation, sperm storage, delayed fertilization, delayed implantation, and embryonic diapause. Females generally give birth to one two two pups per litter, but in some species in the genus Lasiurus, litter sizes may reach 3 or 4 individuals (e.g. Lasiurus borealis, L. seminolus, and L. cinereus).

Key Reproductive Features: iteroparous ; seasonal breeding ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); viviparous ; sperm-storing ; delayed fertilization ; delayed implantation ; embryonic diapause

At birth, newborn bats weigh between 10 and 30% of their mother's weight, putting a large energetic strain on pregnant females. All newborn bats are completely dependent on their mothers for both protection and nourishment. This is true even in Pteropodidae, where pups are born with fur and open eyes. Microchiropterans tend to be more altricial at birth.

Aside from the few monogamous bat species, where males contribute to feeding and protecting young, all parental care in bats is provided by females. Some males defend feeding territories for their harems, thereby contributing indirectly to the survival of their young after birth. Bats cannot fly when they are born, so young bats either remain in the roost while their mothers forage, or cling to their mothers' during flight. Females of many species form maternity colonies while they are lactating and rearing young. When the young are left in the roost as the mother forages, they cluster together to keep warm. Upon their return, mothers and their respective infants can identify each other by their vocalizations and scent, and thus can successfully reunite. In some species, females will communally care for young, with "babysitters" caring for the cluster of young while their roost-mates forage.

Juveniles grow quickly and can usually fly within 2 to 4 weeks of birth. They are weaned shortly thereafter. Thus, lactation is relatively short, but metabolically demanding.

Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Male, Female, Protecting: Male, Female)

  • Hill, J., J. Smith. 1984. Bats: A Natural History. Austin: University of Texas Press.
  • Vaughan, T., J. Ryan, N. Czaplewski. 2000. Mammalogy, 4th Edition. Toronto: Brooks Cole.
  • Nowak, R. 1991. Order Chiroptera. Pp. 190-194 in Walker's Mammals of the World, Vol. 1, 5th Edition. Baltimore: Johns Hopkins University Press.
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Evolution and Systematics

Evolution

Discussion of Phylogenetic Relationships

View Chiroptera Tree

Tree from Simmons and Geisler (1998).

The fossil record of bats extends back at least to the early Eocene, and chiropteran fossils are known from all continents except Antarctica. Icaronycteris, Archaeonycteris, Hassianycteris, and Palaeochiropteryx, unlike most other fossil bats, have not been referred to any extant family or superfamily. These Eocene taxa are known from exceptionally well-preserved fossils, and they have long formed a basis for reconstructing the early evolutionary history of Chiroptera (see review in Simmons and Geisler, 1998).

Smith (1977) suggested that these taxa represent an extinct clade of early microchiropterans ("Palaeochiropterygoidea"). In contrast, Van Valen (1979) argued that these fossil forms are representatives of a primitive grade ancestral to both Megachiroptera and Microchiroptera ("Eochiroptera"). Novacek (1987) reanalyzed morphology of Icaronycteris and Palaeochiropterx and concluded that they are more closely related to Microchroptera than to Megachiroptera. Most recently, Simmons and Geisler (1998) found that Icaronycteris, Archaeonycteris, Hassianycteris, and Palaeochiropteryx represent a series of consecutive sister-taxa to extant microchiropteran bats.

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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage

Barcode of Life Data Systems (BOLD) Stats
                                        
Specimen Records:31,841Public Records:19,507
Specimens with Sequences:21,827Public Species:593
Specimens with Barcodes:21,016Public BINs:1,044
Species:962         
Species With Barcodes:776         
          
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Barcode data

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Locations of barcode samples

Collection Sites: world map showing specimen collection locations for Chiroptera

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Conservation

Conservation Status

Approximately 25% of all species within Chiroptera (nearly 240 species) are considered threatened by the International Union for the Conservation of Nature (IUCN). At least twelve species have gone extinct in recent times. Megachiropterans tend to be more at risk than microchiropterans (34% and 22% of species, respectively), but both groups are facing substantial threats from habitat loss and fragmentation. Destruction of, or disturbances to, roost sites is particularly problematic for bats. Pesticide use also indirectly harms bats that eat insects or plant products that have been chemically treated. Species with relatively small geographic ranges and/or that are ecologically specialized tend to be at greatest risk.

In recent years, the general public has become increasingly aware of the beneficial roles that bats play in ecosystems and their unique and amazing life histories. A wealth of research now demonstrates that bats are a vital component of many ecosystems and an important resource for humans. Efforts to protect bats have increased. For example, many caves that serve as large hibernacula are fixed with gates that allow access by bats, but not by humans. Rather than trying to eradicate bats from homes and neighborhoods, many people are placing bat houses in their yards to give bats appropriate roosting habitat. In the United Kingdom, all bats and bat roosts are protected by law. Several large roost emergences, including evening emergences from a roost under the Congress Avenue Bridge in Austin, Texas, draw millions of tourists each year. Conservation organizations like Bat Conservation International (www.batcon.org) have growing memberships among the general public and run many successful bat conservation projects, including projects in the developing world designed to increase awareness and appreciation.

  • Fenton, M. 1997. Science and the conservation of bats. Journal of Mammalogy, 78/1: 1-14.
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Relevance to Humans and Ecosystems

Benefits

Economic Importance for Humans: Negative

Although bats are often perceived as much more of a threat to human interests than they actually are, bats may negatively impact humans in at least two ways. Some species roost in human dwellings and can become a nuisance. This is particularly true if a large colony takes up residence in a home, producing a great deal of guano and an unpleasant odor.  Bats also carry and transmit rabies. In general, bats rarely transmit rabies to other species, including humans and domestic animals. Vampire bats, on the other hand, regularly transmit the disease to domestic cattle, representing a large financial burden for the cattle industry in the New World tropics. Rabies is transmitted through saliva and other body fluids and vampire bats exhibit several behaviors which make them especially effective vectors of the disease (e.g., social grooming and food sharing). Their feeding habits result in their saliva contacting the blood of other animals, which is an ideal situation for rabies transmission.

Negative Impacts: injures humans (carries human disease); causes or carries domestic animal disease ; household pest

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Economic Importance for Humans: Positive

Although many people consider bats to be harmful pests, bats play pivotal roles in ecological communities and benefit humans in numerous ways. Many species of insectivorous bats prey heavily on insects that transmit diseases or are crop pests. In addition, bat guano (feces) is often used to fertilize crops. Many tons of guano are mined each year from caves where bats aggregate in large numbers. In other words, some species eat crop pests and excrete crop fertilizer! Evidence continues to accumulate in support of the immense economic benefit of insectivorous bats for the agricultural industries worldwide. Frugivorous bats are important seed dispersers, helping promote the diversity of fruiting trees in the tropics. Bats that eat pollen and nectar are important pollinators, and some plants they pollinate are economically important to humans, such as Agave and bananas (Musa). Larger bats, such as pteropodids are sometimes eaten by humans.

Recently, common vampire bats have become an important focus of medical research. Vampire bats are generally considered a significant threat to human interests because they regularly transmit rabies to cattle (and sometimes to people). However, the anticoagulant protein in their saliva ("Desmoteplase") is being studied in an effort to help prevent blood clots in humans, such as those being treated for stroke.

The increasing popularity of bats has led to a booming ecotourism industry, often surrounding large roost emergences, such as those of Mexican free-tailed bats.

Positive Impacts: food ; ecotourism ; source of medicine or drug ; research and education; produces fertilizer; pollinates crops; controls pest population

  • Reddrop, C., R. Moldrich, P. Beart, M. Farso, G. Liberatore, D. Howells, K. Petersen, W. Schleuning, R. Medcalf. 2005. Vampire bat salivary plasminogen activator (desmoteplase) inhibits tissue-type plasminogen activator-induced potentiation of excitotoxic injury. STROKE, 36/6: 1241-1246.
  • Bat Conservation International. 2004. "Bat Conservation International" (On-line). Accessed August 16, 2005 at www.batcon.org.
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