Idionycteris phyllotisAllen's big-eared bat

Geographic Range

Idionycteris phyllotis is found in the mountainous regions of the southwestern United States through central Mexico.


Idionycteris phyllotis primarily dwells in caves in mountainous pine and oak forests. The availability of water holes is a significant factor in habitat selection due to their high rate of evaporative water loss. Nearly all capture sites have been in the vicinity of rocks, such as cliffs or large boulders, their most probable roosting sites.

Physical Description

The defining characters of Idionycteris phyllotis, also known as Allen's Big-Eared Bat, are its large ears (34 to 43 mm) which possess lappets projecting from the base of the ears and extending over the forehead. Idionycteris phyllotis has a total length of 103 to 118mm, a tail length of 44 to 55mm, and a forearm length of 42 to 49 mm. The wing span of I. phyllotis ranges from 302 to 344mm. Dorsal and ventral pelage is long (10mm) and basally black with yellowish gray tips. A patch of white hair occurs at the base of the ears. Females are generally about 5% larger in head and body length, however, there is no difference in forearm length.

  • Range mass
    8 to 16 g
    0.28 to 0.56 oz


Females form maternity colonies during the summer months, from June to late July, where they give birth to and raise their young. Maternity colonies consist of an average of 30 females. Males live separately from the females during this time. Females give birth to a single young.

  • Range number of offspring
    1 to 1


Most I. phyllotis are observed two to three hours after sunset near water. Their flight is characterized by swift, direct movements during open flight and slow, highly maneuverable movements in close quarters. They are also capable of hovering. They emit an audible echolocation signal during open flight. Males and females live in colonies of from 5 to 28 individuals during the non-summer months. Males are solitary and females form maternity colonies during the summer months.

Communication and Perception

Food Habits

Idionycteris phyllotis is an insectivorous bat which feeds mostly by gleaning moths and stationary insects from surfaces.

Economic Importance for Humans: Positive

Because Idionycteris phyllotis is an insectivorous bat it plays an important role in pest control. Bat guano is used as a source of fertilizer, and organisms housed in the guano are used for waste detoxifying.

Economic Importance for Humans: Negative

Bats are known to carry the causative virus of rabies

Conservation Status

Roost disturbance is the greatest threat to Idionycteris phyllotis. Mining activities have caused the relocation or extermination of several bat roosts. Reproduction is shown to decrease after relocation, threatening the survival of the roost. Deforestation removes the feeding environment for the bats, as well as that of their insect prey.

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 Idionycteris phyllotis mortalities as a result of white-nose syndrome, the disease continues to expand its range in North America. (Cryan, 2010; National Park Service, Wildlife Health Center, 2010)


David Alvarado (author), University of Michigan-Ann Arbor, Phil Myers (editor), Museum of Zoology, 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


living in the southern part of the New World. In other words, Central and South America.

World Map

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.


uses smells or other chemicals to communicate


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


having the capacity to move from one place to another.


This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

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

scrub forest

scrub forests develop in areas that experience dry seasons.

seasonal breeding

breeding is confined to a particular season


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


uses touch to communicate


The term is used in the 1994 IUCN Red List of Threatened Animals to refer collectively to species categorized as Endangered (E), Vulnerable (V), Rare (R), Indeterminate (I), or Insufficiently Known (K) and in the 1996 IUCN Red List of Threatened Animals to refer collectively to species categorized as Critically Endangered (CR), Endangered (EN), or Vulnerable (VU).


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


"Allen's (Mexican) Big-Eared Bat (Idionycteris" (On-line). Accessed (Date Unknown) at

Monday, 26-Jan-98. "Data : Species : Mammal : Mexican" (On-line). Accessed (Date Unknown) at

October 20,1997. "Species: Allen's Big-eared Bat (Idionycteris phyllotis)" (On-line). Accessed (Date Unknown) at

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

National Park Service, Wildlife Health Center, 2010. "White-nose syndrome" (On-line). National Park Service, Wildlife Health. Accessed September 16, 2010 at

Warner, R. 1985. INTERSPECIFIC AND TEMPORAL DIETARY VARIATION IN AN ARIZONA. Journal of Mammalogy, 66 (1).: 45-51.