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| Mexican Free-tailed Bat - Tadarida brasiliensis |  
Wingspread: 11.4-12.8 inches. Weight:0.38-0.49 oz.
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The Mexican, Brazilian or American free-tailed bat occurs south through Central America and tropical South America. They are found in the southern two-thirds of the state of Utah.Bats belonging to the family Molossidae, such as this one, are more commonly known as "free-tailed" bats, referring to their tail which extends beyond the tail membrane. This is a highly colonial species with some colonies numbering in the millions. The Mexican free-tailed bat is an inhabitant of mines, caves, buildings and bridges. Females are apparently already pregnant when they come into Arizona in the spring. Young, which weigh up to 25% of their mother's weight at birth, are born into nursery colonies made up of many individual females.
The Mexican free-tailed bat is a highly migratory species with much of the United States population going south to hibernate. These bats are high flying foragers, leaving their roost en masse to forage up to 40 miles away. It appears that the population numbers of this species have declined across its range.
Mexican free-tailed bats occupy a wide variety of habitats, ranging from desert communities through pinion-juniper woodland and pine-oak forests at elevations from sea level to 9,000 feet or more. The largest U.S. populations of free-tailed bats live in the West, with the densest concentrations found in Texas where they form maternity colonies numbering in the millions. They are found throughout Mexico and most of the western and southern U.S. The largest maternity colonies are formed in limestone caves, abandoned mines, under bridges, and in buildings, but smaller colonies also have been found in hollow trees. It is estimated that 100-million Mexican free-tailed bats come to Central Texas each year to raise their young. Nursing females require large quantities of insects that are high in fat, which they obtain by consuming egg-laden moths. The 100 million free-tailed bats living in Central Texas caves consume approximately 1,000 tons of insects nightly, a large proportion of which are agricultural pests. Researchers using Doppler weather radar watch emerging bats ascend to altitudes of 1,000-10,000 feet to feed on migrating cotton boll worm moths, army cut-worm moths, and other costly agricultural pests that migrate north from Mexico. These migratory moths hopscotch across the country each year, reaching rich agricultural land as far north as the Canadian border. The cotton boll-worm moth (a.k.a. corn ear-worm moth) alone, costs American farmers a billion dollars annually. Although the ecological and economic impacts of large colonies are most obvious, even small colonies of bats can significantly impact local insect populations. Mexican free- tailed bats also consume enormous quantities of insects over woodlands and forests, likely including |
| | Big Free-tailed Bat - Nyctinomops macrotus |  
Wingspread: 16.5-17 inches.
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This large free-tailed bat has large "bonnet" ears that extend beyond the nose when laid forward. It is found from northern South America and the Caribbean Islands northward into the western United States. In the fall, these bats apparently migrate to southern Arizona and Mexico. They are found only as far north as southern Utah during the spring and summer, and have been captured in a variety of habitats including ponderosa pine, Douglas-fir, and Sonoran desertscrub. Many of these locations are thought to represent foraging habitat only. They apparently prefer to roost in rock crevices and fissures of tall cliffs in desertscrub habitat.
Big free-tailed bats leave their roost in small groups relatively late in the evening to forage on large moths, crickets, flying ants, and grasshoppers. They have long, pointed wings and are strong flyers, capable of traveling hundreds of miles from their normal range. While foraging, they can emit a loud, piercing chirp which is within the range of human hearing.
Females have one young per year, usually born in June or July. When or where breeding occurs is unknown. Little is known about much of the biology and habitat requirements of this species. The biggest threat to this species, as with most other bat species, is human disturbance at the cliff roosts. |
| | Pocketed Free-tailed Bat - Nyctinomops femorosaccus | Wingspread: 3-14 inches. Weight: 0.3-0.5oz. Body Length: 2-3 inches.
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The pocketed free-tailed bat is a medium sized bat with dark brown to gray fur. It is distinguished by ears that are joined at the base, long narrow wings, and long foot hairs that protrude beyond the toes. The "pocket" for which it is names consists of a membrane that extends the length of the femur. The pocket is not really noticeable, nor is it unique to this species, occurring in other free-tailed bats.
Pocketed free-tailed bats range from southern California and New Mexico, south into Mexico through Baja, Sonora, Durango, and Jalisco at least to Michoacan. It reaches its northern limit of its range in central Arizona.A few acoustic records in southern Utah may be from pocketed free-tail bats, but this has not been confirmed.
It seems to prefer caves and crevices along rocky cliffs in semi-arid desert lands, but has also been known to roost in buildlings. Pocketed free-tailed bats live together in small colonies of less than one hundred individuals. A single young is born during late June or July. Though they are occasionally preyed upon by snakes, their biggest threat comes from humans. |
| | Greater Bonnetted or Western Mastiff Bat - Eumops perotis |  
Wingspread: 20.8-22.4 inches. Weight:2.10 oz.
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This is the largest bat in the United States. The western mastiff bat is a spectacular high-flying predator that roosts in small colonies in cliffs and rock crevices. This bat occurs in three district populations; South America, Cuba, and the southern United States.It occurs in a variety of locations throughout Arizona in the summertime and probably is a year-round resident.Western mastiff bats are known to roost in the Grand Canyon (approx. 50 miles) and forage on the Kaibab Plateau (approx. 30 miles) south of the GSENM.A few acoustic records in southern Utah may be from pocketed free-tail bats, but this has not been confirmed.
Western mastiff bats leave the roost as a group, forage at high elevations for several hours, and then return to the roost en masse. Besides being the largest bat, it is also the loudest bat in the United States. It emits a high pitched, piercing "cheap" every two to three seconds during flight. They are a very vocal bat, uttering a variety of calls that can be heard by the human ear. It's long, narrow wings provide poor maneuverability, requiring a long vertical drop in order to take off. These bats drink water while in flight by gliding over water sources with large open surface areas, such as stock ponds. A single young is born in Arizona in June or July.
The mastiff bat is the largest bat in the U.S., with a wing span approaching two feet. It is found in California, Nevada, Arizona, Texas and Mexico though it is rarely encountered in large numbers. Almost nothing is known about the behavior or status of western mastiff bats. Because they roost in cliff-face crevices and feed high above the ground, they are rarely seen and approach the ground only at a few select drinking sites. This bat is severely limited by available drinking water. Its long, narrow wings preclude it from drinking at ponds less than 100 feet long. Apparently, due in large part to the loss of large natural springs, western mastiff bats are no longer found in many previously occupied areas and may be endangered, though past and present observations are too few to determine their status. |
| | All Photos by M.Siders |
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