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Antrozous palliduspallid bat

By Katie Weber

Geographic Range

Pallid bats range from southern British Columbia through Montana to central Mexico. They occur from the Okanagan valley in British Columbia, south through eastern Washington, Oregon, and California to Baja California Sur, Sonora, Sinaloa, Nayarit, Jalisco, Queretaro, and Nuevo Leon in Mexico. They are found as far east as western Texas, Oklahoma, southern Kansas, southern Wyoming, and southern Idaho. There is a disjunct population on the island of Cuba. (Nowak, 1999; Verts and Carraway, 1998)

Habitat

Pallid bats are also called desert bats because they are mostly found in desert habitats. They roost in a variety of places but favor rocky outcrops. They also occur in oak and pine forested areas and open farmland. Roosting sites are variable, depending on what is available. They can be found roosting in caves, rock crevices, mines, hollow trees, and buildings. Pallid bats in Oregon have been documented roosting in rock piles, piles of burlap sacks, and hollow trees. They use day roosts that are semi-dark, as long as there is some sort of cover. Night roosts for resting between feeding intervals are near day roosts, but are not the same as day roosts. Pallid bats prefer darkness, shelter from wind and rain, and an easy escape if they are disturbed. Roosts are usually near a source of water, but this does not appear to be a main requirement for roosting locations. Winter roost locations are not well known for A. pallidus. Specimens captured in Oregon during the winter were not anywhere near summer roosting sites. Winter specimens were found in narrow crevices; this may contribute to the difficulty of locating these individuals in the winter. A study done by Vaughan and O’Shea (1976) showed that pallid bats arrive in Arizona sometime around March or April and then depart again in November. They were observed using vertical and overhanging cliff crevices, but during the hottest part of the day they were found to move to deeper, cooler crevices to maintain a more suitable body temperature. (Nowak, 1999; Vaughan and O’ Shea, 1967; Verts and Carraway, 1998)

Physical Description

Adults range from 60 to 85 mm long from head to tail. The tail can be 35 to 57 mm alone. Forearm length is 45 to 60 mm long and body weight ranges from 17 to 28 grams. Their fur has a woolly feel with a cream-yellow to light brown color on the dorsum and very pale to white color on the venter. This species has a U-shaped ridge on the top of the muzzle with the nostrils located underneath the ridge on the front of its muzzle. The face has small wart-like pararhinal glands that produce a skunk-like odor, which is thought to be used as defense mechanism. The ears are large with a long, pointed tragus; the tragus is half as long as the ear itself. Their ears have serrated outer edges that are not joined at the base. They have a high brain case with a rostrum that is greater than the half the length of the skull and have a dental formula: I 1/2, C 1/1, P 1/2, M 3/3, with a total of 28 teeth. There is a geographical color variation in pallid bats and this genus has six subspecies; A. p. pallidus, A. p. bunkeri, A. p. koopmani, A. p. minor, A. p. obscurus, A. p. pacificus, and A. p. packardi. (Nowak, 1999; Verts and Carraway, 1998)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    17 to 28 g
    0.60 to 0.99 oz
  • Range length
    60 to 85 mm
    2.36 to 3.35 in
  • Average basal metabolic rate
    0.104 W
    AnAge

Reproduction

Males in California undergo an increase in testes size during the month of August until September and then regress by mid-October. Males are present in nursery colonies as well as in separate single-sex groups. Breeding takes place in early October and continues sporadically throughout the winter. Bats in captivity mate in October and November, some have been observed mating in January and February. In captivity, mated females ovulate and become pregnant with an increase in ambient temperature. Ambient temperature may effect when wild populations produce young, especially if the seasonal temperatures are changing from year to year. (Nowak, 1999; Verts and Carraway, 1998)

Females can retain the sperm in the uterus throughout the winter until spring when fertilization occurs. The gestation period lasts from 53 to 71 days and young are born between May and June. They usually have twins, but about 20 percent of births are single. Birth weight is near 3 grams. The young open their eyes about five days after their birth and begin to fly at 4 to 5 weeks after birth. At 6 to 8 weeks after birth they are weaned and are able to breed in their first year. (Verts and Carraway, 1998)

  • Breeding interval
    Breeding occurs once yearly.
  • Breeding season
    Pallid bats breed beginning in October and throughout the winter.
  • Range number of offspring
    1 to 3
  • Average number of offspring
    2
    AnAge
  • Range gestation period
    53 to 71 days
  • Range weaning age
    6 to 8 weeks
  • Average time to independence
    1 years
  • Average age at sexual or reproductive maturity (female)
    1 years
  • Average age at sexual or reproductive maturity (female)
    Sex: female
    365 days
    AnAge
  • Average age at sexual or reproductive maturity (male)
    1 years
  • Average age at sexual or reproductive maturity (male)
    Sex: male
    365 days
    AnAge

The young are born in an altricial state. They have closed eyes and their ears are folded against the head with a few hairs visible only under magnification. The mothers will carry the young during her foraging flights for the first few days after birth. Females only lactate for 2 to 3 months and do not nurse young that are not their own. The young have recurved cusps on their deciduous teeth. This allows the young to grasp the nipple of the females in order to prevent detatchment in flight. Mothers will stay with their young for 12 months after the young are flying on their own. This is also when most will fly in family groups of two or three when returning to their day roost. The day roosts may not always be the same place, allowing the young bats to learn how to seek out the vocal calls when the colony swarms around the chosen day roost sight. Males do not care for offspring. (Nowak, 1999)

  • Parental Investment
  • altricial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • extended period of juvenile learning

Lifespan/Longevity

Individuals of A. pallidus in the wild have been known to live for at least nine years and captive populations have had individuals live for up to eleven years. (Verts and Carraway, 1998)

Behavior

Pallid bats are highly social. A single colony can range from 12 to 100 bats. About 95% of groups consist of at least 20 individuals, with the largest colony consisting of 162 bats. Pallid bats stay in their roosts longer into the evening before emerging to hunt than other species of bats. Time of emergence will change with season. During summer males and females can be found roosting together or in single-sex colonies. Males won’t usually join roosts of females with young until the young have begun foraging on their own. Pallid bats are very good at climbing and crawling, but are slower flyers with little maneuverability when compared to smaller bats. Pallid bats are agile when crawling, allowing them to move efficiently on the ground. When returning to their day roosts, pallid bats swarm and vocalize around the entrance for 15 to 45 minutes, calling individuals back to the roost. This swarm will evaluate the entrance until one bat enters and calls the rest into the roost. When they settle in summer day roosts they maintain a body temperature of around 30° C. When in torpor they may move to a cooler place in the roost in order to maintain that body temperature. During rest intervals in night roosts, pallid bats will also enter torpor for 2 to 5 hours, depending on the season. Pallid bats do not migrate, except for short distances to winter hibernacula. (Nowak, 1999; Verts and Carraway, 1998)

Home Range

Home range sizes are not reported.

Communication and Perception

Pallid bats locate other members of their group using vocalizations. Once they locate each other they congregate in a roosting area before reentering torpor. There are four main calls used when individuals are locating one another: a directive call that is used to find one another, squabble notes used to space bats when roosting, a buzzing used in agonistic intraspecific encounters, and ultrasonic orientation pulses for communicating exploratory activity to other individuals. (Nowak, 1999; Vaughan and O’ Shea, 1967)

Pallid bats use echolocation to navigate and to find flying prey. They also use their large ears to detect the sounds of prey on the ground, such as the sound of a beetle moving across the ground. (Nowak, 1999; Verts and Carraway, 1998)

Food Habits

Pallid bats have a unique foraging pattern among North American bats. They fly low to the ground (about 15 to 76 centimeters), then dip and rise in swoops in order to grab ground-dwelling prey or slow-flying prey. This pattern allows them to use passive hearing to hear their prey on the ground. They may drop to the ground to grab large, ground-dwelling prey. They also forage for insects among leaves and flowers. They will take smaller prey in the air using echolocation. Pallid bats take larger prey back to their roosts and remove hard parts, such as wings, legs, and heads, from prey before eating them. Pallid bats have two nightly foraging periods with a roosting time in between. They prey mainly on large flying and ground-dwelling insects, including beetles (Coleoptera), crickets, katydids, and grasshoppers (Orthoptera, including Jerusalem crickets Stenopelmatus fuscus), cicadas (Homoptera), moths (Lepidoptera), spiders (Araneae), scorpions (Scorpiones), centipedes (Chilopoda). They sometimes take small lizards and mice. (Barbour and Davis, 1969; Nowak, 1999; Vaughan and O’ Shea, 1967)

  • Animal Foods
  • mammals
  • reptiles
  • insects
  • terrestrial non-insect arthropods

Predation

Pallid bats feed on the ground, which makes them vulnerable to terrestrial predators and injury. Terrestrial predators may include snakes, cats, foxes, coyotes, and raccoons. Adult and young bats are mainly preyed on by snakes or crepuscular and nocturnal raptors, mainly owls. (Verts and Carraway, 1998)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Pallid bats play an important role as predators of desert insects. Pallid bats visit flowers in their hunt for insects, and are natural, indirect pollinators of several species of cactus. (Verts and Carraway, 1998)

  • Ecosystem Impact
  • pollinates

Economic Importance for Humans: Positive

Pallid bats eat many insects, reducing the population size of pest insects. (Arroyo-Cabrales and de Grammont, 2008)

  • Positive Impacts
  • research and education
  • controls pest population

Economic Importance for Humans: Negative

Pallid bats roost in man-made structures, causing occasional damage from droppings or odor problems. This is also a problem because bats, along with other mammals, carry rabies virus. Although transmission of rabies to humans is rare, roost proximity to human habitation may be a concern. (Nowak, 1999)

  • Negative Impacts
  • injures humans
    • carries human disease

Conservation Status

The IUCN Red List status for Antrozous pallidus is Least Concern. This is mainly due to their widespread distribution and presumed large population. They occur in many protected areas, leading researchers to believe that populations are unlikely to decline in the foreseeable future. They have been placed at low risk to least concern in the past. These bats are susceptible to mild disturbances which cause them to abandon their roosting sites. Humans also may disrupt their prey species with pesticides, offsetting prey populations. Wildlife managers are taking action to manage and monitor habitat to avoid disturbance. (Arroyo-Cabrales and de Grammont, 2008)

Temperate North American bats are now threatened by a fungal disease called “white-nose syndrome.” This disease has devastated eastern North American bat populations at hibernation sites since 2007. The fungus, Geomyces destructans, grows best in cold, humid conditions that are typical of many bat hibernacula. The fungus grows on, and in some cases invades, the bodies of hibernating bats and seems to result in disturbance from hibernation, causing a debilitating loss of important metabolic resources and mass deaths. Mortality rates at some hibernation sites have been as high as 90%. While there are currently no reports of Antrozous pallidus mortalities as a result of white-nose syndrome, the disease continues to move westward across North America. (Cryan, 2010; National Park Service, Wildlife Health Center, 2010)

Other Comments

Pleistocene-Holocene fossils of pallid bats are found in Arizona, New Mexico, and California.

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Katie Weber (author), University of Alaska Fairbanks, Link E. Olson (editor, instructor), University of Alaska Fairbanks.

Glossary

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.

World Map

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.

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.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

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.

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.

forest

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

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

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).

motile

having the capacity to move from one place to another.

native range

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

nocturnal

active during the night

polygynandrous

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

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

social

associates with others of its species; forms social groups.

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.

suburban

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

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.

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

vibrations

movements of a hard surface that are produced by animals as signals to others

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.

References

Arroyo-Cabrales, J., de Grammont. 2008. "Antrozous pallidus" (On-line). IUCN 2008. 2008 IUCN Red List of Threatened Species. Accessed November 10, 2008 at http://www.iucnredlist.org/details/1790.

Barbour, R., W. Davis. 1969. Bats of America. Lexington, KY: University of Kentucky Press.

Cryan, P. 2010. "White-nose syndrome threatens the survival of hibernating bats in North America" (On-line). U.S. Geological Survey, Fort Collins Science Center. Accessed September 16, 2010 at http://www.fort.usgs.gov/WNS/.

National Park Service, Wildlife Health Center, 2010. "White-nose syndrome" (On-line). National Park Service, Wildlife Health. Accessed September 16, 2010 at http://www.nature.nps.gov/biology/wildlifehealth/White_Nose_Syndrome.cfm.

Nowak, R. 1999. Walker's Mammals of the World, Sixth Edition, Volume 1. Baltimore and London: The Johns Hopkins University Press.

Vaughan, T., O. O’ Shea. 1967. Roosting ecology of the pallid bat, Antrozous pallidus. Journal of Mammalogy, 67: 91-102.

Verts, B., L. Carraway. 1998. Mammals of Oregon. Berkley: University of California Press Berkeley / Los Angeles / London.

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