Nyctinomops femorosaccuspocketed free-tailed bat

Geographic Range

Nyctinomops femorosaccus, the pocketed free-tailed bat, is a member of the Family Molossidae and occurs in the southwestern United States and Mexico. In the United States, this species inhabits southern California, central Arizona, southern New Mexico, and west Texas. The range of pocketed free-tailed bats extends southward into the Mexican plateau as far south as Michoacán. Populations of this species are non-migratory or locally migratory, with no migrations exceeding 200 km. The easternmost extent of its range is Big Bend National Park in Texas, where it was first documented in 1967. Big Bend and the surrounding areas are the only areas of Texas where the species is known to reside. A single specimen was recorded as far north as Carlsbad Caverns in New Mexico. One study has shown that these bats are yearlong residents in southern Arizona and that they may migrate in the winter, although it is unsure how far they travel. (Ammerman, et al., 2012; Hoffmeister, 1970; NatureServe, 2015; Schmidly, 2004)


The pocketed free-tailed bat inhabits dry, semiarid desert areas. They can be found from sea level to about 2,250 m in altitude. Roosting sites include rocky outcrops, buildings, and crevices in cliffs and small caves. In California, they were once found to be sharing a crevice with Eumops perotis. Nyctinomops femorosaccus was found at the narrow, upper end of the space and Eumops perotis was found at the lower, wider end, showing a distinct partitioning of niche space. Pocketed-free tailed bats are usually found near large open water sources from which they drink early in the evenings. (Kays and Wilson, 2009; Kumirai and Jones, 1990; Schmidly, 2004)

  • Other Habitat Features
  • caves
  • Range elevation
    0 to 2,250 m
    0.00 to ft

Physical Description

Nyctinomops femorosaccus is a small to medium-sized bat. The pelage is red-brown to gray-brown ventrally and slightly paler dorsally. Like other bats in the family Molossidae, N. femorosaccus posses a long tail that extends beyond the uropatagium. Pocketed free-tailed bats average 112 mm in body length and weigh 10-14 g. Their average measurements (in mm) are: length of tail, 46; length of hind foot, 10; length of ear, 23; length of forearm, 46. Females are slightly smaller than males in average measurements, especially cranially. The dental formula is 1/2, 1/1, 2/2, 3/3=30. Pocketed free-tailed bats have a wingspan of about 345 cm. The common and scientific names refer to a small, pocket-like fold of skin on the underside of the uropatagium, which does not have a perceivable purpose. Nyctinomops femorosaccus have long, narrow wings and have a rapid, complete wing beat when flying. There are vertical wrinkles on the lips along the muzzle. Pocketed free-tailed bats possess long hairs above the uropatagium that extend beyond the normal pelage length. These hairs most likely serve a sensory function for when the animal backs into its roosting crevice. The dorsum hairs are bicolored and nearly white at the base, and the ears are joined at the middle of the head above the forehead. These characteristics serve to distinguish N. femorosaccus from Tadarida brasiliensis, which is similar in size and appearance. Nyctinomops femorosaccus are differentiated from N. lauticaudatus by a smaller thumb, larger body size, fewer and finer hairs on the membranes, and thicker ears. Nyctinomops femorosaccus is smaller and has a noticeably less inflated braincase than N. aurispinosus. (Ammerman, et al., 2012; Bat CREW, 2004; Bowers, et al., 2004; Kumirai and Jones, 1990; Schmidly, 2004)

  • Sexual Dimorphism
  • male larger
  • Range mass
    10 to 14 g
    0.35 to 0.49 oz
  • Average length
    112 mm
    4.41 in
  • Average wingspan
    345 cm
    135.83 in


Nothing specifically is known about the mating behavior of pocketed free-tailed bats, but it is suggested that males and females roost together. One study on Nyctinomops laticaudatus in Mexico, to which N. femorosaccus is closely related and allopatric, suggested that they engage in a promiscuous mating system. Another member of the same genus, Nyctinomops macrotis, engages in separation of sexes and maternity colonies while pups are being raised. Further insights on the reproductive behavior of this species are needed. (Ammerman, et al., 2012; Kumirai and Jones, 1990; Milner, et al., 1990; Ortega, et al., 2010)

Females generally mate in the spring and give birth in late June to July, giving birth to one offspring annually. Like other bats, females engage in delayed fertilization and mate just prior to ovulation. The gestation period is about 70-90 days. When pups are born they weigh about 3-4 grams, which is about 22% of the mother's body weight. Pups are weaned and flying by mid-to-late August. (Arroyo-Cabrales and Álvarez-Castañeda, 2015; Grzimek, 1990; National Park Service, 2016; Whitaker Jr., 1996)

  • Breeding interval
    once annually
  • Breeding season
  • Range number of offspring
    1 (low)
  • Range gestation period
    70 to 90 days
  • Range weaning age
    1 to 1.5 months

The parental investment of the pocketed free-tailed bat is not documented, but, like other molossids, females are most likely solely responsible for the care of the pups forming maternity colonies that are separate from males. (Grzimek, 2003)


There is no information on the exact longevity of this species. Another molossid, Tadarida brasiliensis, has been found to live at least 8 years in the wild and up to 12 years in captivity. Bats in general have some of the longest life spans relative to their body size, with many species living over 20 years. (Magalhaes and Costa, 2009; Podlutsky, et al., 2005)

  • Typical lifespan
    Status: wild
    8 (low) years
  • Typical lifespan
    Status: captivity
    12 (low) years


Nyctinomops femorosaccus are colonial roosters that usually nest in small colonies of fewer than 100 individuals. However, one colony in Big Bend National Park was observed to contain up to 700 individuals. When leaving their roosting areas, pocketed free-tailed bats drop down and immediately gain elevation and speed. Since this species does not roost in large caves, they do this without the need for echolocation to maneuver out of their roosting sites. Pocketed free-tailed bats have been seen hitting the surface of a water source and drinking in mid-flight. One observation made by Philip Krutzsch of a colony in California noted that N. femorosaccus started leaving the roost at 6:15 pm and exited by twos and threes for another half hour. Other reports have said that this species leaves roosts well after dark, and captures in mist nets set over water in the summer have peaked several hours after sunset. This may suggest later emergence in the summer or that these bats start foraging immediately and frequent water sources later in the night. It appears that a few individuals will leave the roost and act as scouts, and then return to coax the rest out. (Ammerman, et al., 2012; Benson, 1940; Bowers, et al., 2004; Kumirai and Jones, 1990; Schmidly, 2004)

Home Range

The home range size of this species is not known. One study on Nyctinomops macrotis individuals determined that they had a total activity area of 29,590 ha and a maximum distance traveled from the roost of 25.3 ± 4.9 km. (Corbett, et al., 2008)

Communication and Perception

At night, Nyctinomops femorosaccus drop from their perch and emit a loud high-pitched call as they fly. Pocketed free-tailed bats typically use frequencies of 17-18 kHz to locate their prey. High-pitched squeaks and other chatter-like calls can easily be heard from their daytime roosting sites. These bats, like other molossids, have scent glands on their chest and throat which are likely used for social or mating interactions. (Ammerman, et al., 2012; Grzimek, 2003; Whitaker Jr., 1996)

Food Habits

Pocketed free-tailed bats are insectivorous. The majority of their diet consists of moths (Lepidoptera), but they also feed on smaller flying insects including wasps and flying ants (Hymenoptera), beetles (Coleoptera), flies (Diptera), and true bugs (Hemiptera). The entire bodies of small insects are eaten, but only the bodies of large moths are consumed. Nyctinomops femorosaccus emits low frequency (around 17-18 kHz) echolocation calls during flight to locate their prey. One study of these bats in Big Bend did not record any resource partitioning with Tadarida brasiliensis, but it did record a possible dietary shift in March and September from Lepidopterans to Hemipterans as the dominant food source. (Ammerman, et al., 2012; Kumirai and Jones, 1990; Matthews, et al., 2010)

  • Animal Foods
  • insects


There is not much extensive research on the predation of Nyctinomops femorosaccus, but their remains have been found in owl pellets and from a California lyre snake that was captured from a pocketed free-tailed bat roosting site. (Jones, et al., 1972; Krutzsch, 1944)

  • Known Predators
    • owls, California lyre snake (Trimorphodon vandenburghi)

Ecosystem Roles

Nyctinomops femorosaccus is the sole host of a species of wing mite, Trombicula spathi. This bat species has also been described as hosts for other ectoparasites such as Microtrombicula merrihewi, an intranasal chigger, Speleocola tadaridae, also a chigger, and Chiroptonyssus venezolanus, a mite. The coccidian endoparasite, Eimeria tadarida, has also been described from N. femorosaccus. (Davis and Loomis, 1971; Duszynski, et al., 1988; Loomis and Tanigoshi, 1968; Loomis and Webb, 1969; Whitaker Jr. and Easterla, 1975)

Commensal/Parasitic Species
  • mites, chiggers, coccidians

Economic Importance for Humans: Positive

Pocketed free-tailed bats, like other bats, are beneficial in that they consume large amounts of insects, including agricultural pests. Guano from bat colonies can be collected and used as a nitrogen-rich fertilizer. (Grzimek, 2003)

  • Positive Impacts
  • produces fertilizer
  • controls pest population

Economic Importance for Humans: Negative

Nyctinomops femorosaccus can be carriers of the rabies virus, which can be a health concern for humans and other animals. Other health concerns include the fungus, Histoplasma capsulatum, which grows in bat guano and can cause histoplasmosis in humans via inhalation. (Grzimek, 2003)

Conservation Status

Pocketed free-tailed bats are listed as species of least concern because they have a wide distribution with some apparent large subpopulations. These bats are also located in several protected areas. Although Nyctinomops femorosaccus are not considered a species of concern, they are still uncommon throughout some parts of their range and their populations have not been studied very extensively. It is possible that these bats may be threatened by habitat loss and the use of pesticides with their chief food source, moths. Further research is needed to determine the nature of their apparent rarity. (Arroyo-Cabrales and Álvarez-Castañeda, 2015; NatureServe, 2015; Schmidly, 2004)

Other Comments

There are no recognized subspecies within Nyctinomops femorosaccus. The generic name, Nyctinomops, means "resembling a night feeder". Prior to 1981, Nyctinomops had been grouped within Tadarida and is now recognized as a distinct genus. (Kumirai and Jones, 1990)


Katelyn Lasater (author), Texas A&M University, Jessica Light (editor), Texas A&M University, Tanya Dewey (editor), University of Michigan-Ann Arbor.



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


uses sound to communicate


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.


an animal that mainly eats meat

causes or carries domestic animal disease

either directly causes, or indirectly transmits, a disease to a domestic animal


Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.


uses smells or other chemicals to communicate


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

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.


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.


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


An animal that eats mainly insects or spiders.


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.


active during the night


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


uses touch to communicate


Living on the ground.


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


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