Geography 316:  Biogeography     In progress 12/16/2003

The Biogeography of  the  Bat (Choeronycteris mexicana)

by Elisa Bravo, student in Geography 316  Fall 2003

Thank you for visiting our site. This web page was written by a student in Geography 316: Biogeography and edited by the instructor, Barbara Holzman, PhD.  All photos and maps are posted with specific copyright permission for the express use of education on these web pages. The students have tried to be as accurate as possible with the information provided and sources and references are cited at the end of each page.

Species Name: Choeronycteris mexicana

 

Kingdom: Animalia Phylum:   Chordata Class:     Mammalia Order:     Chiroptera Family:    Phyllostomidae Genus:     Choeronycteris Species:  Choeronycteris mexicana
	Bat Conservation International, Inc., 2002.

Description of Species:

The Mexican long-tongued bat is a medium size bat with gray or brown fur above and lighter fur below. It has a long slender nose with a small arrowhead shape on the tip about 0.2 inches high. It has big eyes and a very small tail that extends less than halfway to end of interfemoral membrane. The characteristic that gives this bat its common name is its tongue. The tongue is very long, it can extend to one-third of its body length. The upper incisors are small, and do not fill the space between the canines, also there are no permanent lower incisors, but 1 to 4 teeth may persist in adults. The average measures are. Weight: 10-25 gr. wingspan: 33-38 cms, total length: 85mm, tail: 1/3 of an inch (10mm), hind foot: 0.44-0.56 inches (14mm), ear: 16mm, forearm: 1.68-1.92 inches (44mm) (AGFD 2003, CWHRS 2003)

Bat Conservation International, Inc., 2002.

Natural History:

Their peak activity occurs 1.5 hours after sunset and then, it continues at low levels until about three hours after sunset.  These bats are less social than other colonial bats, and it s not very common that they roost with other bat species. In their roosts, they do not hang close together; usually they hang about two to five centimeters apart from each other. Usually they roost only by one foot; this allows them to rotate 360 degrees to watch for predators or intruders. Populations usually consist of 15 or fewer individuals but some can be as large as 40-50 individuals. (AGFD 2003, BCI 2003, CWHRS 2003) Most of their roost sites are located near a water source and near areas of riparian vegetation. These sites are mostly located in desert canyons, deep caves, mines tunnels, or rock fissures. But they also can be rarely found in urban environments like buildings for day roosts. 

This species inhabits altitudes ranging from 4,000 to 6,200 feet. They are known to live in a variety of habitats ranging from desert, montane, riparian, piñon-juniper habitats; and from arid thorn shrub to tropical deciduous forest and mixed oak-conifer forest. (AGFD 2003,CWHRS 2003) Historically it ranged from Venezuela to the north through Central America and Mexico to southeastern Arizona, southwestern New Mexico, and San Diego, California. Choeronycteris mexicana is a migratory species. Mexican long-tongued bats spend the winter in Mexico, but they do not hibernate. Then they move north to the southwestern United States, up to southern Arizona, in the summer.  They migrate to take advantage of the food resources; they migrate in the winter to follow the flowering food plants like agave and yucca. 

They feed on fruit, nectar, pollen, and probably insects. The diet usually is about 75% nectar, 25% pollen, fruits occasionally are eaten and insect use is rare. (CWHRS 2003) They especially feed on night blooming flowers like paniculate agaves and occasionally fruit of columnar cacti. Their uniquely large tongue and the lack of lower incisors help in lapping up flower nectar and pollen. As described before, their tongues can extend up to a third of their body length, a feature that makes them uniquely capable of reaching nectar deep inside an agave or cactus flowers. There are also reports of bats feeding from Hummingbird feeders. These feeders provide food for those bats arriving to northern destinations when food sources are not yet available. The long-tongued bat primarily is a nectar feeder.

Females segregate from the males. It is believed that only adult females move north from Mexico into the United States with the males remaining "in the southern part of the range during the time that young are being nourished by the mothers in the north." Only one young per year is born, in mid to late June and early July but it may be as late as September in Mexico. Birth usually lasts for about 15 minutes, a neonate in a remarkably advanced state of development. The young are born well-furred for additional warmth in the cool mountain canyons where the mothers roost. Females are known to carry their young in flight but babies grow rapidly and can probably fly within 2-3 weeks. (AGFD 2003)

Evolution:
 

There are hundreds of species of bats, belonging to the single order Chiroptera. As mammals, bats come from a long lineage of animals that arose from the Therapsid reptiles in the Triassic (120 million years ago). These reptiles were small, nocturnal, insectivorous, and had highly developed senses of smell and hearing. Evolving the ability to fly required a complex change in anatomy of the animals that became bats.

Most researchers believe that bats and primates evolved from arboreal insect eaters, and that bats went through a gliding stage. The wings of bats can be thought of as two sections, the membranes supported by the arms and the membrane supported by the fingers provides the thrust and maneuverability. For arboreal animals, gliding used less energy and was safer. In general, animals with the ability to control their direction would have had a selective advantage, so the hand wings that define the order would have evolved rapidly. Flight probably evolved before the sophisticated echolocation, but echolocation is believed to have been what facilitated the diversification of bats into the wide variety of niches in which they live today. (Lyttle 1999) Bats, after rodents are the most numerous group of mammals in terms of species. There are approximately 925 species of bats, 20% of all known living mammal species. (Carstens 2003) In some tropical areas, there are more species of bats than of all other kinds of mammals combined.

The order Chiroptera is broken down into two sub-orders, Megachiroptera, the "big bats", and Microchiroptera, the "little bats". The Megachiroptera includes one family Pteropodidae and about 166 species; they all feed primarily on plant material, fruit, nectar or pollen. The Microchiroptera includes the other 16 families, around 759 species, the majority insectivorous. But many of this species have become specialized for other kinds of diets. Some are carnivorous eating rodents, other bats, reptiles, birds, amphibians or fish.  Many others feed on fruit, some are specialized for extracting nectar from flowers  (like the C. mexicana), and one group of three species feeds on blood.

The earliest fossil bat is a remarkably well-preserved and fully formed bat. It is known as the Icaronyteris index, and dates from approximately 50 million years ago. The I. index appears to be modern, and based on the size and shape of its cochlea (a spiral-shaped cavity of the inner ear that resembles a snail shell and contains nerve endings essential for hearing), it is believed to have been able to echolocate. (UM 2003) Since the time of I. index bats have diversified to fill a wide variety of niches. But it is a more interesting subject to determine the evolutionary history of bats before the I. Index. Since the I. Index comes from a microchiropteran species, this suggests that the split between micro and mega bats occurred earlier. There are more fossils, but most of the knowledge of bat evolution relies on other types of evidence.

The theory about bat evolution is actually controversial, concerning whether the two major groups of bats are monophyletic (descended from, or derived from one stock or source). This issue is not settled, but today, most evidence seems to favor the hypothesis that they are monophyletic; the most recent common ancestor shared by the two groups would also be classified as a bat. Since most bats eat insects, evolutionists have traditionally taught that bats evolved from primitive insectivores, like shrews, moles, etc. on the other hand, fruit-eaters merely modified their diet due to ecological pressures. (Carstens 2003)

Studies with mitochondrial DNA have shown that all bats are closely related, and separate from primates. There is evidence as well, of an existing muscle complex in the wings of all bats that is different from birds and all gliding mammals. (Carstens 2003) The bat monophyly hypothesis states that the megachiroptera and microchiroptera are close relatives in an evolutionary sense. If this were true, then their shared characteristics, including the ability to fly, would have been present in their most recent common ancestor. This implying as well that there was only one origin of powered flight in mammals.

Proponents of the hypothesis that bats are diphyletic pointed out that many similarities between megachiroptera and microchiroptera involve the flight mechanism. So there is the possibility of convergent evolution of aerial locomotion, instead of a shared ancestry. This mechanism can be the one responsible for the similarities between megachiropteran and microchiropteran bats.

In the early 1980s J. D. Smith suggested that megabats and microbats evolved separately, because there are many physiological differences between the two other than just size.

• Microbats have a complicated shoulder joint and a claw only on the thumb. Megabats have a simple shoulder joint but a claw on both the thumb and first finger.

• Microbats use echolocation. Megabats mainly rely on their eyesight.

• Microbats teeth are designed for prey. Megabats teeth grind plant parts.

• Many microbats have the ability to hibernate through cold winters. Megabats can live only in the tropics, needing a year-round food supply.

It has also been suggested that Megachiroptera is more closely related to Dermoptera and Primates than to Microchiroptera. In 1986 Dr. John Pettigrew further proposed that flying foxes closely resemble primates and that along with flying lemurs that also have their own order but do not actually fly, share a common ancestor with the primates. He based his conclusions on research that showed that primates have unique neural pathways in the brain, having to do with vision, and that these pathways were so unique that it was thought that they distinguish primates from non-primates. From his research, he discovered that megabats have these specific pathways, so he proposed that they are really all primates, sharing a common ancestor. This theory implies that flight in bats evolved later in evolutionary history, and that it is only a coincidence that it is similar to flight in microbats.

 

	Nancy B. Simmons. Tree of Life web project

Distribution::

• Bats in general, are nearly worldwide in distribution. The greatest varieties of bats are found in the tropical regions, but still some species inhabit the temperate regions.

• Phyllostomidae family: It is mostly found in the tropical and subtropical regions of the New World, from the southwestern United States and the West Indies to northern Argentina.

• C. mexicana: it is found in the southwestern United States through  most of Mexico, and in Central America, El Salvador and Honduras. In the United States, it occurs primarily in the southern tip of California, near the San Diego area, in southern Arizona, in southwestern New Mexico, and the southern tip of Texas. Rare collections have been done in the Grand Canyon National Park, in northern Arizona, and there is a single record from Las Vegas, Nevada. (CWHRS 2003)

The C. mexicana is common in semi-desert and desert environments but these bats can live in a variety of habitats like thorn scrubs, saguaro-desert, semi-desert grasslands, oak woodland and tropical deciduous forest. (AGFD 2003, BCI 2003, CWHRS 2003) Their distribution is related to their unique diet, pollen and nectar, especially from agave plants. They are most commonly found in desert canyons, where vegetation like ocotillo, yucca, agave, manzanita, evergreen oak, and juniper occurs. In Mexico, they can also be found at higher altitudes of oak and ponderosa pine habitats. They can be found at altitudes ranging from 4,600 to 6,200 feet. (AGFD 2003)

The C. mexicana is a migratory species. It is known to occur in the United States most commonly during the summer, when blooming plants provide pollen and nectar, the basis of their diet. Then they move to Mexico during the colder months.

 

© Bat Conservation International, Inc., 2002.

Other interesting issues:

Choeronycteris mexicana comes from the Greek word choiros that means pig (because the nose looks kind of like a pig) and the word nykteris that means bat. Mexicana, describes its major distribution area, and where the species was first described.

There are some human threats to this species. It is an extremely sensitive species to disturbance, especially at the roost sites; if disturbed, they can leave the site on which they depend. Mining, mine closing, mine reclamation and development are threats to the Choeronycteris mexicana. (Eguiarte 1987, Howell 1981) They are also important pollinators and seed dispersers for about 60 species of agave plants. Popular tequila, the best-known Mexican liquor is made from distilled agave juices; it economically it contributes to a multi-million dollar industry. The problem is that agave propagation, without bats, falls to 1/3000th of normal. The bat-plant association is so strong that the disappearance of one would threaten the survival of the other. (Ducummon 2000) Since long-term sustainable food supply is important for its survival, the loss of agave plants and other food plants can endanger the species. Recently there has been a significant loss in agave plants, due to over harvesting and general habitat loss, and this may endanger the species. Although it is not listed as endangered, fewer than 400 bats have been seen in the United States since 1906. (CWHRS 2003)

Bibliography :  

1. Arizona Game and Fish Department. 2003. Choeronycteris Mexicana. Unpublished abstract compiled and edited by the Heritage Data Management System, Arizona Game and Fish Department, Phoenix, AZ.

2. Baker, Robert J. Hood, Craig S. Honeycutt, Rodney L. Phylogenetic Relationships and Classification of the Higher Categories of the New World Bat Family Phyllostomidae. In: Systematic Zoology. Vol. 38, No. 3 (Sep. 1989), 228-238.

3. Bat Conservation International. Bat Species: U.S.Bats: Choeronycteris Mexicana. :\murcielagomexicano\murcielago mexicano_files. October 2003

4. California Wildlife Habitat Relationships System. M020 Mexican Long-tongued Bat Choeronycteris mexicana.In: file:///A:/murcielagomexicano/murcielago%20mexicano_files. october 2003.

5. Carstens, Bryan C. Lundrigan, Barbara L. Myers, Philip. A Phylogeny of the Neotropical Nectar-Feeding Bats (Chiroptera: Phyllostomidae) Based on Morphological and Molecular Data. In: Journal of Mammalian Evolution, Vol. 9, No. 1 /2, June 2002.

6. Carstens, Bryan. Informational Articles. On the Origin of Bats. In: file:///A:/murcielagomexicano/murcielago%20mexicano_files. November 2003.

7. Ducummon, Sheryl L. Ecological and Economical Importance of Bats. 2000. Bat Conservation International, Inc. Proceedings of Bat Conservation & Mining Interactive Forum. St. Louis, Missouri on November 14-16, 2000

8. Eguiarte, Luis; Martinez Del Rio, Carlos; Arita, Hector. El Nectar y El polen Como recursos: el papel ecologico de los visitantes a las flores Pseudobombax ellipticum (H.B.K) Dugand Biotropica. Vol.19, n.1, marzo 1987. 74-82.

9. Howell, D.H., Schropfer Roth, Barbara. Sexual Reproduction in Agaves: the benefits of bats; the cost of semelparous advertising. In: Ecology. Vol. 62. N.1. Feb. 1981. 1-7

10. Lyttle, Ron. Bats and Evolution. In: http://www.creationism.org/batman/bats.htm. 1999. November, 2003.

11. Pettigrew, J. D. 1986. Flying primates? Megabats have the advanced pathway from eye to midbrain. Science 231: 1304-1306.

12. Smith, J. D., and G. Madkour (1980). Penial Morphology and the Question of Chiropteran Phylogeny, Proceedings of the 5th International Bat Research Conference, Texas Tech Press, pp. 347-365.

13. The University of Michigan. Museum of Zoology. Animal Diversity Web. Order Chiroptera. Bats.  By: Philip Myers In: file:///A:/murcielagomexicano/murcielago%20mexicano_files. November, 2003.

14. Tree of life we project. Order Chiroptera (bats).In:  http://murcielagomexicano/murcielago%20mexicano_files. By: Nancy B. Simmons and Tenley Conway. November 2003.

send comments to bholzman@sfsu.edu
 

Geog 316 homepage        Back to Geography home page           Back to SFSU homepage