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.
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.
- Habitat Regions
- temperate
- terrestrial
- Terrestrial Biomes
- savanna or grassland
- forest
- scrub forest
- Other Habitat Features
- suburban
- agricultural
- caves
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
.
- Other Physical Features
- endothermic
- heterothermic
- bilateral symmetry
- Sexual Dimorphism
- sexes alike
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.
- Mating System
- polygynandrous (promiscuous)
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.
- Key Reproductive Features
- iteroparous
- seasonal breeding
- gonochoric/gonochoristic/dioecious (sexes separate)
- sexual
- viviparous
- sperm-storing
- delayed fertilization
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.
- Parental Investment
- altricial
-
pre-fertilization
- provisioning
-
protecting
- female
-
pre-hatching/birth
-
provisioning
- female
-
protecting
- female
-
provisioning
-
pre-weaning/fledging
-
provisioning
- female
-
protecting
- female
-
provisioning
- 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.
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.
- Key Behaviors
- troglophilic
- flies
- nocturnal
- motile
- sedentary
- hibernation
- daily torpor
- social
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.
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.
- Perception Channels
- visual
- tactile
- acoustic
- ultrasound
- echolocation
- vibrations
- chemical
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.
- Primary Diet
- carnivore
- 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.
- 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.
- Ecosystem Impact
- pollinates
Economic Importance for Humans: Positive
Pallid bats eat many insects, reducing the population size of pest insects.
- 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.
- 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.
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.
Other Comments
Pleistocene-Holocene fossils of pallid bats are found in Arizona, New Mexico, and California.
Additional Links
Contributors
Tanya Dewey (editor), Animal Diversity Web.
Katie Weber (author), University of Alaska Fairbanks, Link E. Olson (editor, instructor), University of Alaska Fairbanks.
- 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.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- 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.
- forest
-
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
- scrub forest
-
scrub forests develop in areas that experience dry seasons.
- suburban
-
living in residential areas on the outskirts of large cities or towns.
- agricultural
-
living in landscapes dominated by human agriculture.
- 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.
- 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.
- 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.
- polygynandrous
-
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
- 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).
- seasonal breeding
-
breeding is confined to a particular season
- sexual
-
reproduction that includes combining the genetic contribution of two individuals, a male and a female
- viviparous
-
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
- 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.
- 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.
- 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.
- nocturnal
-
active during the night
- motile
-
having the capacity to move from one place to another.
- sedentary
-
remains in the same area
- 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.
- social
-
associates with others of its species; forms social groups.
- acoustic
-
uses sound to communicate
- chemical
-
uses smells or other chemicals to communicate
- visual
-
uses sight to communicate
- tactile
-
uses touch to communicate
- acoustic
-
uses sound to communicate
- ultrasound
-
uses sound above the range of human hearing for either navigation or communication or both
- 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.
- vibrations
-
movements of a hard surface that are produced by animals as signals to others
- 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.
- carnivore
-
an animal that mainly eats meat
- insectivore
-
An animal that eats mainly insects or spiders.
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.