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Corynorhinus mexicanusMexican big-eared bat

By Angie Leon

Geographic Range

Mexican big-eared bats (Corynorhinus mexicanus) are a Nearctic species. They are generally found as far as north as the border of New Mexico, and Arizona to as far south as Puebla, Mexico. These bats are absent in Central Mexico, between Ciudad Juarez and the city of Leon do not show any of these species, until as far southeast as Monterrey, Mexico. The range of these bats appears to form an uneven “U” shape, where they have been documented as far north as the Border of New Mexico and Arizona, and there have been rare occurrences in Utah. A disjunct population is located on the northern tip of the Yucatan Peninsula, which includes the state of Merida. (Arroyo-Cabrales, 2015)

Habitat

Mexican big-eared bats can be found in dry, subtropical environments with pine-oak Pinus englemanii forests in high elevations (1460 to 3500 m) surrounded by dry lowlands. These bats are generally found roosting in caves and mines. Research of these bats' roosting sites has found that when their typical habitats are disturbed, these bats will find shelter in abandoned houses. Sexes of these bats roost and hibernate together and occasionally even with other species that are closely related to them, such as Townsend’s big-eared bats Corynorhinus townsendii. In some cases, during the spring and summer mating season, females are found in their own maternity colonies. When roosting, these Mexican big-eared bats hang around 5 to 10 m apart, either in pairs or alone. The roost caves typically are at least 50 m deep, and maintain temperatures less than 10°C in winter and above 16°C the rest of the year. (Arroyo-Cabrales, 2015; Black, 1970; Cockrum and Musgrove, 1964; Lopez-Gonzalez and Torres-Morales, 2004)

  • Range elevation
    1460 to 3500 m
    4790.03 to 11482.94 ft

Physical Description

Mexican big-eared bats have a total length ranging from 90mm-103mm with their forearms measuring 39.3mm-45.2mm. Tumilson (1992) reported captured bats with masses ranging from 5.0g-8.7g in males and 7.5g-9.5g in females. Males and females generally are alike in terms of size and weight metrics.

Their hair is bicolored and darker than other species in Corynorhinus. These bats' dorsal and ventral colors vary from gray-brown to black. Their faces are usually paler than the rest of their body. Mexican big-eared bats’ noses are simple with glandular bulges on their muzzle. Their long ears are united in the center at the base. These bats have tails of 41 to 51mm that are contained within the uropatagium. During resting periods, the ears of this species are bent back and curved, similar to a ram's horns. When awoken, their ears extend upwards.

Mexican big-eared bats have a short cranium. Their rostrum is short and depressed, and their brain case is wide and deep. The average cranial measurements of females and males 15.1mm-15.3mm. Their dental formula is 2123/3133 totaling to 36 teeth. (Piaggio and Perkins, 2005; Sanchez-Hernandez, et al., 2016; Tumlison, 1992)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    39.3 to 45.2 g
    1.39 to 1.59 oz
  • Range length
    90 to 103 mm
    3.54 to 4.06 in

Reproduction

Mexican big-eared bats breed once annually. Reproduction patterns can be affected by many environmental factors (e.g., food availability, time of rainy season). Testis require an internal temperature below 10 degrees C to produce sperm, therefore making it a determining factor in choosing a roosting site. Males prepare for the mating season by experiencing testis enlargement that generally begins around the months of May and June. Males' masses will increase due to the development of their reproductive organ. There are no studies reporting the mating behaviors of Mexican big-eared bats. Based on the other species in their genus, males will mate by giving an audible vocalization, which is then followed by head-nuzzling. Mexican big-eared bats likely follow a similar pattern. Male Mexican big-eared bats are polygynous, but no information was provided suggesting whether or not females were polyandrous. Other members of their genus have polyandrous females, so it's suspected that female Mexican big-eared bats do the same. (Leon-Galvan, et al., 2017; Tumlison, 1992)

Mexican big-eared bats reproduce annually. Spermatogenesis will occur in the summer. The male bats go through a testis enlargement beginning in May-June and reaching their peak in August. Their testis can increase their mass by 40 times compared to their mass during sexual inactivity. The enlarged testis of the bats will decrease in size and return back to their original size by November.

The expression of the libido and sex glands are fully developed by autumn. Copulation typically begins around October and November with mating being completed by the end of November. Testes will be completely regressed around this time. Males’ reproductive organs will reach their smallest masses between February and April. During this time, females are typically pregnant. There have been studies that show the occurrence of sperm storage in the female bats. Female Mexican big-eared bats are inseminated in the autumn but are not detected pregnant until the months of January or February. They give birth to 1 pup per pregnancy.

Gestation periods of Mexican big-eared bats have not been studied in depth but are speculated to be similar to the other two bats in their genus – Townsend’s big-eared bats (Corynorhinus townsendii) and Rafinesque's big-eared bats (Corynorhinus rafinesquii). Townsend’s big-eared bats have a gestation period that ranges from 56-100 days. Bats in this genus give live birth to one pup at a time. The average weaning age for for the genus Corynorhinus is 4-6 weeks. Females will be sexually mature by the summer, and males will take up to a year to become sexually mature. (Arenas-Rios, et al., 2007; Leon-Galvan, et al., 2017; Tumlison, 1992)

  • Breeding interval
    Mexican big-eared bats breed once annually
  • Breeding season
    October-November
  • Average number of offspring
    1

Female Mexican big-eared bats protect their single young beginning from the gestation period until they wean off their mother's milk. Bats are known to influence newborns through major sensory systems. These bats do so by milking which allows for a direct biochemical influence with their pup. Newborn pups will attach themselves to their mothers to feed during the day and night. Mother and pup interactions have not been studied for Mexican big-eared bats but is speculated to be similar to Townsend big-eared bats (Corynorhinus towsendii). Once their young are able to independently fly and forage on their own, there is no other relationship between the mother and its pup. Males do not contribute to parental investment beyond the act of mating. (Tumlison, 1992)

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

Lifespan/Longevity

Mexican big-eared bats' lifespan in the wild has not been studied in depth. Lifespan is speculated to be similar to the other bats in their genus, such as Townsend's big-eared bats (Corynorhinus townsendii) which have an average lifespan of 20.5 years. Mexican big-eared bats have not been kept in captivity. (Wilkinson and South, 2002)

Behavior

Mexican big-eared bats are a nocturnal species that can be found singly or in pairs and located away from light. They roost 10-15m from the entrance of their chosen cave. Preference of caves is based on the size and temperature of the cave. These bats roost in caves with temperatures less than 10° Celsius in the winter and above 16° Celsius the rest of the year. When hibernating these bats will cling by their feet with their head against their chest and their back bowed. Their tail will fold under their body and cover their abdomen (Tumilson 1992).

Distance traveled when finding roosting sites and foraging varies among bat species but is based on wing morphology. These bats have low wing loading and low aspect ratio. Their wings are adapted for the use of hovering, and foraging. Mexican big-eared bats forage by echolocation. These bats have the smallest wing morphology in comparison to the Townsend's big-eared bats (Corynorhinus townsendii) and Rafinesque's big-eared bats (Corynorhinus rafinesquii). Mexican big-eared bats are thought to be limited in their ability to travel long distances because of relatively smaller wings than others in the genus. They forage up to a few kilometers near their roost. Distance traveled could be due to other factors such as the season, sex, conditions for reproduction, and the accessibility of food. (Lopez-Gonzalez and Torres-Morales, 2004; Tumlison, 1992)

Home Range

Due to the small wing morphology, Mexican big-eared bats cannot travel as far as other species in their genus. There have not been studies of Mexican big-eared bats' home range but Townsend's big-eared bats males limit distance traveled from their roosting site and stay close to maternity roosts. This could be in order for the males to have easy mating access to females. These bats will travel to different roost sites generally around the same area. (Cockrum and Musgrove, 1964; Morales-Malacara and Lopez, 1990; Tumlison, 1992)

Communication and Perception

The forms of communication used by Mexican big-eared bats have not been studied in depth but are assumed similar to related bats in the genus Corynorhinus. Bats within this genus navigate with echolocation. Townsend's big-eared bats (Corynorhinus townsendii) use low-frequency pulses for longer periods while foraging and frequencies below 20kHz for communication.

Although Mexican big-eared bats have not been studied greatly during mating, female bats have been found pregnant around April and lactating between May and July. Townsend's big-eared bats mate with different partners continuously during their breeding periods. The males will make their mating calls to females, and if accepted, the males will rub their faces around the females. Townsend's big-eared bat males scent-mark to communicate with their mates by using the excretion from the glands on their face. It is thought that Mexican big-eared bats follow a similar pattern in using chemical and tactile efforts in mating. (Arenas-Rios, et al., 2007; Tumlison, 1992)

Food Habits

The diet of Mexican big-eared bats has not been studied, but is speculated to be similar to Townsend’s big-eared bats (Corynorhinus townsendii) and Rafinesque’s big-big eared bats (Corynorhinus rafinesquii). Members of the genus Corynorhinus have diets that are made up primarily of moths, beetles, and other small insects. Townsend’s big-eared bats have a diet that consists of 80% moths. The bats forage by using echolocation in which they use low-frequency signals to find their prey. (Leon-Galvan, et al., 2017; Tumlison, 1992)

  • Animal Foods
  • insects

Predation

There are no known predators of Mexican big-eared bats. Because of these bats’ nocturnal behavior, predators will prey on these bats during roosting hours. (Rodriguez-Tobon, et al., 2016; Tumlison, 1992)

Ecosystem Roles

Mexican big-eared bats and their effect on the ecosystem have not been studied in depth. Although the data are scarce Mexican big-eared bats were recorded with six parasites. Ectoparasites found on these bats include bat flies (Trichobius corynorhini), mites (Macronyssus cyclaspis, Ornithonyssus pipstrelli, Spinturnix americana, Microtrumbicula carmenae), and soft ticks (Carios yumatensis). These bats had the highest percentage of infestation of mites Spinturnix americana, an ectoparasite common in the family Vespertilionidae. (Wilkinson and South, 2002)

Commensal/Parasitic Species

Economic Importance for Humans: Positive

There is no significant economic importance Mexican big-eared bats provide to humans. These bats are major predators of certain moths and pests, but no studies have been performed to confirm any positive impact.

Economic Importance for Humans: Negative

Mexican big-eared bats have not been studied in depth, and have not currently shown any negative economic importance to humans.

Conservation Status

Mexican big-eared bats are currently categorized as "Near Threatened" according to the IUCN Red List. There are no current conservation statuses in CITES appendices, the United States Endangered Species Act list, or the State of Michigan list.

Although the population is not severely fragmented there is a decreasing population trend of mature adults. These bats currently have a status of being Near Threated due to human disturbances. These bats have been found roosting and hibernating in mines, but when their habitat is disrupted they have been found to relocate to abandoned homes. Intrusions such as recreation and housing development threaten these bats, habitats and disturb roost sites. The ongoing urban sprawl is encroaching on the habitat of these bats.

Currently, conservation actions include land and water protection and site/area protection. Research still needs to be done regarding population size, distribution, threats, and actions for the nearly threatened bat species. Reducing the disturbance of mines which serve as hibernacula could be a possible conservation action. Researchers suggest that bat gates could be added to mines that house Mexican big-eared bats. Additional research on the impacts of mining pollution and other mining activities should be implemented. (Arroyo-Cabrales, 2015; Lopez-Gonzalez and Torres-Morales, 2004)

Contributors

Angie Leon (author), Radford University, Layne DiBuono (editor), Radford University, Lindsey Lee (editor), Radford University, Kioshi Lettsome (editor), Radford University, Karen Powers (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

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.

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

colonial

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.

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).

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

polygynous

having more than one female as a mate at one time

scrub forest

scrub forests develop in areas that experience dry seasons.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

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

social

associates with others of its species; forms social groups.

suburban

living in residential areas on the outskirts of large cities or towns.

tactile

uses touch to communicate

terrestrial

Living on the ground.

visual

uses sight to communicate

viviparous

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

References

Arenas-Rios, E., M. Leon-Galvan, P. Mercado, R. Lopez-Wilchis, D. Cervantes, A. Rosado. 2007. Superoxide dismutase, catalase, and glutathione peroxidase in the testis of the Mexican big-eared bat (Corynorhinus mexicanus) during its annual reproductive cycle. Comparative Biochemistry and Physiology Part A: Molecular and Integrative Physiology, 148/1: 150-158.

Arroyo-Cabrales, J. 2015. "Corynorhinus mexicanus" (On-line). The IUCN Red List of Threatened Species Version 2018-1 e.T17599A7164082. Accessed September 08, 2018 at http://dx.doi.org/10.2305/IUCN.UK.2008.RLTS.T17599A7164082.en.

Black, H. 1970. Occurrence of the Mexican big-eared bat in Utah. Journal of Mammalogy, 51/1: 190.

Cervantes, M., E. Arenas-Rios, M. Angel, R. Leon-Galvan, D. Lopez-Wilchis. 2008. Spermatozoa epididymal maturation in the Mexican big-eared bat (Corynorhinus mexicanus). Systems Biology in Reproductive Medicine, 54/4-5: 196-204.

Cockrum, E., B. Musgrove. 1964. Additional records of the Mexican big-eared bat, Plecotus phyllotis (Allen), from Arizona. Journal of Mammalogy, 45/3: 472-474.

Leon-Galvan, M., A. Rodriguez-Tobon, R. Vigueras-Villasenor. 2017. Evidence of apoptosis in the testicular blood vessels of Corynorhinus mexicanus bats characterized by seasonal reproduction. Frontiers in Reproductive Science, 1: 49-73.

Lopez-Gonzalez, C., L. Torres-Morales. 2004. Use of abandoned mines by long-eared bats, Genus Corynorhinus (Chiroptera: Vespertilionidae) in Durango, Mexico. Journal of Mammalogy, 85/5: 989-994.

Morales-Malacara, J., R. Lopez. 1990. Epizoic fauna of Plecotus mexicanus (Chiroptera: Vespertilionidae) in Tlaxcala, Mexico. Journal of Medical Entomology, 27/4: 440-445.

Piaggio, A., S. Perkins. 2005. Molecular phylogeny of North American long-eared bats (Vespertilionidae: Corynorhinus): Inter- and intraspecific relationships inferred from mitochondrial and nuclear DNA sequences. Molecular Phylogenetics and Evolution, 37/3: 762-775.

Rodriguez-Tobon, A., R. Fierro, M. Leon-Galvan, E. Cortes-Barberena, E. Arenas-Rios. 2016. Tyrosine phosphorylation as evidence of epididymal cauda participation in the sperm maturation process of Corynorhinus mexicanus bat. Acta Zoologica, 97/3: 310-318.

Sanchez-Cordero, V., P. Illoldi-Rangel, S. Sarkar, A. Townsend Peterson. 2005. Deforestation and extant distributions of Mexican endemic mammals. Biological Conservation, 126/4: 465-473.

Sanchez-Hernandez, C., M. Romero-Almaraz, G. Schnell, M. Kennedy, T. Best, R. Owen, S. Gonzalez-Perez. 2016. Bats of Colima, Mexico. Norman, Oklahoma: University of Oklahoma.

Tumlison, R. 1992. Plecotus mexicanus. Mammalian Species, 401: 1-3.

Villegas-Guzman, G., M. Vargas. 2015. Ectoparasites associated to two species of Corynorhinus (Chiroptera: Vespertilionidae) from the Guanaceví mining region, Durango, Mexico. Journal of Medical Entomology, 42/2: 125-7.

Wilkinson, G., J. South. 2002. Life history, ecology and longevity in bats. Aging Cell, 1/2: 124-131.

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