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Myotis occultusArizona myotis

By Sydney Jenkins

Geographic Range

The Arizona myotis (Myotis occultus) is found in the western United States and Mexico. It is commonly found in Arizona and New Mexico and is present, but less common, in southern Colorado and southern Utah. Myotis occultus was originally found along the Colorado River in California, but has not been seen in the state since 1967. There is a record of the bat in Texas, though it was very unusual and has not been found there since the early 1900s. The range of the Arizona myotis in Mexico is not very definite as it is often found as far south as Chihuahua, Mexico but there have been isolated sightings near Texcoco, Mexico. (Arroyo-Cabrales and Alvarez-Castaneda, 2008; Barbour and Davis, 1969; Kunz and Racey, 1998)

Habitat

Myotis occultus is often found in temperate and terrestrial biomes and in deserts, woodlands, and caves. Of these three habitats, this bat is most commonly found in pine forests at an elevation of 2,000 to 3,000 meters.

During the summer this species has been known to roost in different man-made structures such as bridges and attics of buildings. Myotis occultus may even share its day roosts with other subspecies of Myotis such as the mouse-eared bat (Myotis yumanensis) and the cave myotis (Myotis velifer.)

Females and males live separately during the summer and maternity colonies have been found in ponderosa pines (Pinus ponderosa) and in timbers of a highway bridge in California. In the winter Arizona myotis hibernate in caves and abandoned buildings. (Andrusiak and Hogan, 2012; Arroyo-Cabrales and Alvarez-Castaneda, 2008; Barbour and Davis, 1969; Diamond, et al., 2015)

  • Other Habitat Features
  • caves
  • Range elevation
    2,000 to 3,000 m
    to ft

Physical Description

This species has an average weight ranging from 7 to 9 grams and a wingspan of 24 to 25 centimeters. The forearms of Myotis occultus have been measured to be between 36 and 41 millimeters. This bat has tawny, light brown, dark brown or golden-brown fur. Its ears are usually black, dark brown, or light brown, as are its wings and feet.

Myotis occultus is morphologically similar to little brown bat (Myotis lucifugus) but there are slight differences in its appearance, as the little brown bat is larger than the Arizona myotis in wingspan, length, and mass. Myotis occultus typically has a distinct sagittal crest while Myotis lucifugus does not have one. Most bats of the genus have two premolars, but a potentially distinguishing feature of the Arizona myotis is that it often only has one premolar behind the upper canines, whereas members of the genus Myotis usually have two. The Arizona myotis has teeth that are larger than most Myotis. Its maxillary tooth row is usually greater than 5.5 mm. However, other researchers contend that these physical features simply represent variation within the species Myotis lucifugus, with Arizona myotis representing the subspecies Myotis lucifugus occultus. ("Arizona myotis, Myotis occultus", 1998; Arroyo-Cabrales and Alvarez-Castaneda, 2008; Barbour and Davis, 1969; Harvey, et al., 2001; Valdez, et al., 1999)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    7 to 9 g
    0.25 to 0.32 oz
  • Range length
    8.5 to 9.0 cm
    3.35 to 3.54 in
  • Range wingspan
    24 to 25 cm
    9.45 to 9.84 in

Reproduction

Mating between male and female Myotis occultus occurs in the fall. During this time there is more movement than usual as large aggregations of Arizona myotis swarm at hibernacula and outside caves. Beyond this, there is not much information about Arizona myotis and mating behavior, though inferences can be made from other species of Myotis.

In the case of the greater mouse-eared bat (Myotis myotis) both sexes are promiscuous and have multiple partners throughout the mating season. According to Zahn and Dippel (1997), mating behavior for Myotis myotis usually means females will travel to male roosting sites to mate for an average of four days and will mate with several different males. Also, Myotis myotis males will attempt to mate with other males during mating season. ("Life history accounts for species in the California Wildlife Habitat Relationships System", 1990; Barbour and Davis, 1969; Geluso and Mink, 2008; Schmidly, 1994; Zahn and Dippel, 1997)

Mating of male and female Myotis occultus occurs in the fall. Rather than fertilization occurring directly after mating between the sexes, the sperm remains in the reproductive tract of the female until the next spring. That spring, fertilization of the single ovary will take place shortly before the bats leave their winter habitats. While pregnant, females and males will separate into different roosts. The female maternity roosts will periodically change sites and may be located in buildings, abandoned houses, crevices in a highway bridge, and snags. Nursery sites of female Arizona myotis are warmer than regular roosting sites due to the high growth rates of young.

Arizona myotis has an average gestation period of 50-60 days with young usually born between June-August. According to Barbour and Davis (1969) a study was conducted in 1963 where 41 pregnant females were observed on June 4 and had not given birth, but by June 29 most of them had. The young varied from barely having fur and weighing 1.8 grams to 6.6 grams, completely covered in fur, and nearly ready to fly. Most of the time there is only one young born per female, although Harris (1990) reports a few records of twins. At approximately three weeks old the young have weaned and by the time they are four weeks old they are able to fly and feed by themselves.

Female Myotis occultus reach sexual maturity within their first year and are ready to breed during that time. Male Myotis occultus, however, do not reach sexual maturity until their second year. Arizona myotis are iteroparous, meaning they have multiple reproductive cycles throughout their lifetime. ("Life history accounts for species in the California Wildlife Habitat Relationships System", 1990; Barbour and Davis, 1969; ; Hayward, 1963; Schmidly, 1994)

  • Breeding interval
    Males and females mate multiple times throughout breeding season, though only one young is born to each female.
  • Breeding season
    Mating begins in the fall though fertilization does not occur until early spring.
  • Range number of offspring
    1 to 2
  • Average number of offspring
    1
  • Range gestation period
    50 to 60 days
  • Average weaning age
    3 weeks
  • Range time to independence
    3 to 4 weeks
  • Average age at sexual or reproductive maturity (female)
    1 years
  • Average age at sexual or reproductive maturity (male)
    2 years

Although males have been found in maternity colonies in the summer, they are not present when the females are rearing young. The young are nursed by their mothers and are gradually introduced to their adult diet during the first three weeks of their lives. About the time they have weaned they are able to fly on their own. ("Arizona myotis, Myotis occultus", 1998; "Life history accounts for species in the California Wildlife Habitat Relationships System", 1990; Barbour and Davis, 1969)

  • Parental Investment
  • female parental care
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • provisioning
      • female
    • protecting
      • female

Lifespan/Longevity

The average lifespan of Myotis occultus is 1-2 years. The first winter has the highest mortality for young as they are smaller and have less fat stored than adults. Because of this, young will remain active in the fall longer than most adults in order to build up their fat reserves as much as possible. According to Harris (1990) the maximum recorded age of Myotis occultus is 31 years.

There are no records of lifespan in captivity for Myotis occultus as it is not kept in captivity. ("Life history accounts for species in the California Wildlife Habitat Relationships System", 1990)

  • Range lifespan
    Status: wild
    31 (high) years
  • Average lifespan
    Status: wild
    1-2 years
  • Typical lifespan
    Status: wild
    1 to 2 years

Behavior

Arizona myotis is a nocturnal bat that usually emerges from their roosts at dusk. There is a high activity peak two hours after dusk and another before dawn as the bats are feeding and flying before returning to their roosts to sleep. Arizona myotis may enter torpor daily outside of hibernating season. Generally these bats begin hibernation between September and November and will end hibernation between March and May. However, young remain active later into the fall in order to build up fat reserves for hibernation. While hibernating these bats may remain completely inactive for 90 consecutive days. According to Harris (1990) Arizona myotis are known to make both local and long distance migrations to hibernacula.

They have separate roosts for day, night, hibernation and maternity. Most day roosts consist of buildings (such as abandoned or attics), trees, or under rocks or wood. Night roosts can be very similar to day roosts, perhaps even the same site, though they are usually in more confined spaces and include areas such as bridges. In 1939, Stager (1943) located a colony of of approximately 2000 bats in the horizontal timbers of a large bridge in the Lower Colorado River Valley. In this colony there were three species: Myotis occultus, Yuma myotis (Myotis yumanensis), and Brazilian free-tailed bats (Tadarida brasiliensis mexicana), with Myotis occultus making up about 40% of the bats present. Stager (1943) also noted that free-tailed bats were roosting by themselves, while the two species of Myotis were found roosting together in some of the timbers.

Although specific temperatures have not been recorded, night roosts are usually warmer than others due to the amount of bats in them. Females have maternity roosts in similar sites as day and night roosts, though they also have to roost in locations with a suitable temperature to save energy. Aggregations of Myotis occultus have been reported of having up to 300,000 individuals. Maternity roosts of Myotis occultus have been recorded of having up to 800 females of this species. Hibernation roosts are commonly in caves or mines with temperatures fairly cold though above freezing.

Arizona myotis are able to detect prey at very short distances and are capable of capturing several prey in rapid succession. This species returns to the same feeding area. Feeding usually occurs over water such as lakes, streams, and ponds. ("Arizona myotis, Myotis occultus", 1998; "Life history accounts for species in the California Wildlife Habitat Relationships System", 1990; Barbour and Davis, 1969; Schmidly, 1994; Stagar, 1943)

Home Range

According to Harris (1990) there has been no evidence of territoriality in Arizona myotis. Myotis occultus will travel up to several kilometers between day roosts and feeding sites. However, no home ranges (by area) have been reported in the literature. ("Life history accounts for species in the California Wildlife Habitat Relationships System", 1990)

Communication and Perception

While there is not much information about the communication techniques of Myotis occultus it is nocturnal and echolocates when foraging and flying. It is also known that they are a part of the Myotis 40 kHz call group, which is characterized by frequency of calls ranging from 35 kHz to above 60 kHz.

Like most bats, Myotis occultus has well-developed eyesight which it uses to recognize landmarks during the daytime when flying. Arizona myotis also use tactile channels such as touch and chemical channels such as smell and taste for communication and perception.

Mothers of other members of the genus, such as Myotis myotis, recognize their young through smell and ultrasonic sound and it is likely that Myotis occultus does too. ("Spring 2012 acoustic bat survey quarterly report for the Rio Mesa Solar Electric Generating Facility, Riverside County, California", 2012; Linzey, 2012)

Food Habits

The Arizona myotis has a diet that consists of soft-bodied and hard-bodied insects. In different regions, diet is determined by prey availability. For example, in New Mexico this species has a diet consisting of wasps, mosquitoes, and other soft-bodied insects, but in Colorado, it consists of hard-bodied insects like beetles. Myotis occultus can even consume up to 600 mosquitos per hour.

Harvey et al. (2001) reported that females that are lactating catch larger prey than other females and males. When these bats forage, it usually occurs in lower elevations such as above bodies of water. Common places for the Arizona myotis to forage are orchards and under tree canopies. (Harvey, et al., 2001)

  • Animal Foods
  • insects

Predation

Predators include birds, snakes, small carnivorous mammals (e.g. raccoons Procyon lotor), and mice. This species has dark fur color which allows it to be cryptic. Humans (Homo sapiens) are also predators to bats, as they may disturb them in their caves or they may use different chemicals to keep the bats away from their property. ("Life history accounts for species in the California Wildlife Habitat Relationships System", 1990)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Stager (1943) reported a 1939 study that examined 63 specimen of Myotis occultus from California for parasites. Only two species of bat fleas (Myodopsylla gentilis and Myodopsylla collinsi) were found. Valdez et al. (2009) looked at 202 individuals of Myotis occultus, 52 of which were alive and 150 of which were museum specimens. Of the 2,158 ectoparasites found, 634 were found on the live specimens and 1,524 were found on the museum samples. From this study, it was found that the live specimens had a higher amount of fleas specifically Myodopsylla gentilis, bat mites (Chiroptonyssus robustipes), and chiggers (Leptotrombidium myotis), whereas museum specimens had higher amounts of different species of mites (Alabidocarpus calcaratus and Alabidocarpus nr. eptesicus).

Arizona myotis are insectivores and are prey to birds, snakes, small carnivorous animals and mice. (Barbour and Davis, 1969; Harvey, et al., 2001; Stagar, 1943; Valdez, et al., 2009)

Commensal/Parasitic Species

Economic Importance for Humans: Positive

As Myotis occultus has a diet of insects, this bat might act as a pest controller, which benefits humans. (Harvey, et al., 2001)

  • Positive Impacts
  • controls pest population

Economic Importance for Humans: Negative

Some members of Myotis are known carriers of rabies but infection rates are extremely low, and no cases of humans bitten by rabid bats have been directly attributed to Myotis occultus. ("Bat Exposure and Rabies", 2004)

  • Negative Impacts
  • injures humans
    • carries human disease

Conservation Status

Myotis occultus does not have a special status on the US Federal List of endangered species or CITES. However, it is listed as a species of "Least Concern" according to IUCN Red List.

In some areas in Mexico Myotis occultus can be found in protected areas. Arizona myotis inhabit many man-made structures, such as attics, abandoned buildings, and bridges, and when humans continue their expansion it can benefit this species.

Myotis occultus has suffered declines due to pesticides, disturbance by humans and control efforts by humans. Disturbance during the winter is destructive to this species due to the amount of energy that is used during arousal. Pesticides that are fat-soluble are especially dangerous when used around hibernation and migration times as it causes a depletion of fat reserves saved up for winter. ("Life history accounts for species in the California Wildlife Habitat Relationships System", 1990; Arroyo-Cabrales and Alvarez-Castaneda, 2008; Barbour and Davis, 1969)

Other Comments

According to Barbour and Davis (1969) there have been many arguments that Myotis occultus should be considered a subspecies of Myotis lucifugus but others say there are enough differences, such as cranial measurements, that the Arizona bat should keep its status. Valdez et al. (1999) performed a study by collecting Myotis occultus and Myotis lucifugus and comparing genetics of the two species. This study found Myotis occultus and Myotis lucifugus to be genetically similar with a value over 0.968 for similarity which suggests an extensive gene flow between the species. Valdez et al. (1999) concluded that despite slight physical differences between the species, Myotis occultus should be regarded as a subspecies of Myotis lucifugus. Additional genetic data indicates clearly that Arizona myotis is best considered a subspecies of Myotis lucifugus. (Barbour and Davis, 1969; Piaggo, et al., 2002; Valdez, et al., 1999)

Contributors

Sydney Jenkins (author), Radford University, Cari Mcgregor (editor), Radford University, Zeb Pike (editor), Radford University, Karen Powers (editor), Radford University, April Tingle (editor), Radford University, Jacob Vaught (editor), Radford University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

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

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

crepuscular

active at dawn and dusk

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.

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.

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

fertilization

union of egg and spermatozoan

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).

migratory

makes seasonal movements between breeding and wintering grounds

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.

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

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.

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.

visual

uses sight to communicate

References

Biogeographic Data Branch Sacramento, CA. Arizona myotis, Myotis occultus. Contract No.FG3146WM. Sacramento, California: California Department of Fish and Game. 1998.

National Park Service U.S. Department of the Interior. Bat Exposure and Rabies. N/A. Washington, D.C.: National Park Service U.S. Department of the Interior. 2004.

California Wildlife Habitat Relationships System. Life history accounts for species in the California Wildlife Habitat Relationships System. N/A. Sacramento, CA: California Department of Fish and Game. 1990. Accessed February 27, 2016 at https://nrm.dfg.ca.gov/FileHandler.ashx?DocumentID=2317.

Rio Mesa Solar I, LLC and Rio Mesa Solar II, LLC. Spring 2012 acoustic bat survey quarterly report for the Rio Mesa Solar Electric Generating Facility, Riverside County, California. TN# 66782. La Jolla, California: Rio Mesa Solar I, LLC and Rio Mesa Solar II, LLC. 2012. Accessed February 11, 2016 at http://www.energy.ca.gov/sitingcases/riomesa/documents/applicant/2012-08-17_Spring_2012_Acoustic_Bat_Survey_Quarterly_Report_TN-66782.pdf.

Andrusiak, L., B. Hogan. 2012. Western Bat Working Group. Western bat working group newsletter, 7/3: 8-9.

Arroyo-Cabrales, J., S. Alvarez-Castaneda. 2008. "Myotis occultus" (On-line). The IUCN Red List of Threatened Species: Myotis occultus. Accessed January 28, 2016 at http://www.iucnredlist.org/details/136650/0.

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

Ceballos, G. 2014. Mammals of Mexico. Baltimore, MD: Johns Hopkins University Press.

Diamond, J., R. Gwinn, J. Johnson, H. Telle, G. Diamond. 2015. Population characteristics of big brown bat and Arizona myotis using artificial boosting structures in northern Arizona. Western North American Naturalist, 75/1: 115-126.

Geluso, K., J. Mink. 2008. Use of bridges by bats (Mammalia: Chiroptera) in the Rio Grande Valley, New Mexico. The Southwestern Naturalist, 54/4: 421-429.

Harvey, M., J. Altenbach, T. Best. 2001. Bats of the United States and Canada. Baltimore, MD: The Johns Hopkins University Press.

Hayward, B. 1963. A maternity colony of Myotis occultus. Journal of Mammalogy, 44/2: 279.

Kunz, T., P. Racey. 1998. Bat Biology and Conservation. Washington, D.C.: Smithsonian Institution Press.

Linzey, D. 2012. Vertebrate Biology 2nd Edition. Baltimore, MD: The Johns Hopkins University Press.

Piaggo, A., E. Valdez, M. Bogan, G. Spicer. 2002. Systematics of Myotis occultus (Chiroptera: Vespertilionidae) inferred from sequences of two mitochondrial genes. Journal of Mammology, 83/2: 386-395.

Schmidly, D. 1994. The Mammals of Texas: Revised Edition. Austin, TX: University of Texas Press.

Stagar, K. 1943. Remarks on Myotis occultus in California. Journal of Mammalogy, 24/2: 197-199.

Stager, K. 1957. Records of the spotted bat from California and Arizona. Journal of Mammalogy, 38/2: 260.

Tierpsychol, Z. 1977. How do mother and young of the bat Myotis myotis recognize each other after mother's return from a hunting flight?. National Center for Biotechnology Information, 44/4: 423-431.

Valdez, E., J. Choate, M. Bogan, T. Yates. 1999. Taxonomic status of Myotis occultus. Journal of Mammalogy, 80/2: 545-552.

Valdez, E., C. Ritzi, J. Whitaker. 2009. Ectoparasites of the occult bat, Myotis occultus (Chiroptera: Vespertilionidae). Western North American Naturalist, 69/3: 364-370.

Wimsatt, W. 1970. Biology of Bats. New York, NY: Academic Press, Inc.

Zahn, A., B. Dippel. 1997. Male roosting habits and mating behaviour of Myotis myotis. Journal of Zoology, 243/4: 660.

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