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Myotis vivesifish-eating bat

By Emily Marquez

Geographic Range

The Mexican fishing bat is endemic to the islands and coastal areas on both sides of the Sea of Cortez and the west-central coast of the Baja California peninsula (Arita and Ortega, 1998; Bogan, 1999).

Habitat

Myotis vivesi lives on the islands and coastal areas on both sides of the Sea of Cortez and on the west-central coast of the Baja California peninsula. They forage over water in these areas. They roost in caves or rock crevices, and have also been found living under large flat rocks along the beach (Altringham, 1996).

Physical Description

The Mexican fishing bat is the largest North American member of the genus Myotis, characterized by long, enlarged and laterally compressed claws on the hind feet, elongate feet and legs. The margin of the plagiopatagium is attached to the side of the foot, as in many other members of the subgenus Leuconoe. The skull has a low braincase and broad rostrum.

The wings of the Mexican fishing bat are long and relatively large, with a high aspect ratio (AR) and low wing load (WL). Wings with high aspect ratio allow for highly efficient flight, however, the ability to maneuver well is compromised. Because the bats forage over open water, maneuverability is not a priority. Low wing load allows the bat to carry heavy loads in flight, so carrying prey items is not a problem. These wing features contribute to the bat's foraging style-- slow, low flight over the open water.

Like other fishing bats, the Mexican fishing bat has very large feet and long claws. The toes and large sharp claws are laterally compressed to minimize drag when skimming through the water to catch a prey item. The bat's long calcar folds forward along the lower portion of the hindlimb, so that the uropatagium is out of the way when the bat is fishing.

The fur is fawn to brown, with dark gray at the base. The underparts are whitish. There are a few hairs at the base of its uropatagium on the underside, but on the dorsal surface there is a relatively thick layer on the distal third of the membrane.

(Altringham, 1996; Hill and Smith, 1984.)

  • Average mass
    25 g
    0.88 oz
  • Average mass
    25 g
    0.88 oz
    AnAge
  • Average basal metabolic rate
    0.199 W
    AnAge

Reproduction

Testicles are smallest in January, become descended in June, and reach maximum size in October. Mature spermatozoa are found in males from late July through September. Females give birth to a single young in late May to early June, following a gestation period of 55-65 days (Maya, 1968). The seasonal separation of male spermatogenic activity and female gestation suggests that sperm may be stored by the female, as occurs in some other vespertilionid species. Other reproductive data available in Mammalian Species account (Blood and Clark, 1998).

  • Range number of offspring
    1 to 1
  • Average number of offspring
    1
    AnAge

Lifespan/Longevity

Behavior

The Mexican fishing bat flies low and rather slowly while foraging over open marine lagoons, nearly skimming the water. When it locates a prey item, it gaffs the prey with the long claws of the hind feet and quickly transfers the item to its mouth. They will either feed during flight or retreat to a perch and consume their prey there (Hill and Smith, 1984).

Communication and Perception

Food Habits

The Mexican fishing bat feeds on marine crustaceans and fish. Their fishing behavior is thought to have evolved from feeding on insects floating or swimming in the water. Individuals generally forages over marine lagoons and eat small marine fish, which have a high salt contact. As the bat's habitat is also in an arid region, it has a highly modified urinary system, similar to other organisms that must conserve water. Their digestive tract is similar to that of other carnivorous bat species, with a pyloric region relatively larger than the cardiac region (Altringham, 1996; Hill and Smith, 1984).

Economic Importance for Humans: Positive

No known benefit to humans. Some bats that live in large colonies produce large amounts of guano that can be sold as fertilizer.

Economic Importance for Humans: Negative

No known adverse affect. Some bats can carry rabies, however, it is not easily transmitted to humans (Fenton, 1992).

Conservation Status

Arita and Ortega (1998) have evaluated the Mexican fishing bat as a species of special concern. Specific dangers to the bat's chances for survival are: it is endemic to Baja, has a specialized diet and habitat, and the rapid transformation of its habitat. Because not much is known about the ecology of the Mexican fishing bat, Arita and Ortega recommend data collection on natural history as well as population statistics. The immediate steps recommended are to protect the immediate area in which the species occurs, as well as manage its roosting and feeding habitats.

Contributors

Emily Marquez (author), University of California, Berkeley, James Patton (editor), University of California, Berkeley.

Glossary

Neotropical

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.

brackish water

areas with salty water, usually in coastal marshes and estuaries.

chaparral

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.

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

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.

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.

estuarine

an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.

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.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

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

tactile

uses touch to communicate

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

viviparous

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

References

Altringham, J. 1996. Bats: Biology and Behaviour. Oxford: Oxford University Press.

Arita, H., J. Ortega. 1998. The Middle American Bat Fauna: Conservation in the Neotropical-Nearctic Border. Pp. 295-308 in T Kunz, P Racey, eds. Bat Biology and Conservation. Washington: Smithsonian Institution Press.

Blood, B., M. Clark. 1998. Myotis vivesi. Mammalian Species, 588: 1-5.

Bogan, M. 1999. Family Vespertilionidae. Pp. 139-181 in S Alvarez-Casteñada, J Patton, eds. Mamíferos del noroeste de México. La Paz, Baja California Sur, México: Centro de Investigaciones Biológicas del Noroeste, S.C..

Fenton, M. 1992. Bats. New York: Facts on File.

Hill, J., J. Smith. 1984. Bats: A Natural History. Austin: University of Texas Press.

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