Nyctinomops femorosaccus

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.

• Biogeographic Regions
• nearctic nearctic
  • native native

Habitat

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.

• Habitat Regions
• terrestrial terrestrial

• Terrestrial Biomes
• desert or dune desert or dune
• chaparral chaparral

• Other Habitat Features
• caves

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 .

• Other Physical Features
• endothermic endothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• male larger

Reproduction

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.

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.

• Key Reproductive Features
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• viviparous viviparous
• delayed fertilization delayed fertilization

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.

• Parental Investment
• altricial altricial
• female parental care female parental care

Lifespan/Longevity

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.

Behavior

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.

• Key Behaviors
• flies
• nocturnal nocturnal
• motile motile
• colonial colonial

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.

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.

• Communication Channels
• acoustic acoustic
• chemical chemical

• Perception Channels
• tactile tactile
• echolocation echolocation
• chemical chemical

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.

• Primary Diet
• carnivore carnivore
  • insectivore insectivore

• Animal Foods
• insects

Predation

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.

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 .

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.

• 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.

• Negative Impacts
• injures humans
  • carries human disease
• causes or carries domestic animal disease causes or carries domestic animal disease

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.

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.

Additional Links

Encyclopedia of Life

Contributors

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

References

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