|Scientific Name:||Leptonycteris nivalis|
|Species Authority:||(Saussure, 1860)|
|Taxonomic Notes:||Prior to 1962 specimens of Leptonycteris yerbabuenae were reported as L. nivalis. See Van Den Bussche (1992) for an analysis of phylogenetic relationships of phyllostomid bats based on restriction-site variation in the ribosomal-DNA gene complex.|
|Red List Category & Criteria:||Endangered A2c ver 3.1|
|Assessor(s):||Arroyo-Cabrales, J., Miller, B., Reid, F., Cuarón, A.D. & de Grammont, P.C.|
|Reviewer(s):||Medellín, R. (Chiroptera Red List Authority) & Schipper, J. (Global Mammal Assessment Team)|
Listed as Endangered because of a serious population decline, estimated to be more than 50% over the last 10 years, inferred from trade data, observed shrinkage in distribution and anecdotal information on habitat destruction and/or degradation.
|Range Description:||This species is known from southeast Arizona, south New Mexico, and west Texas (USA) to south Mexico and Guatemala (Simmons, 2005). It occurs from lowlands to 3,500 m (mostly 1,000 to 2,200 m) (Reid, 1997).
The range includes medium to high elevations in northern and central Mexico, southwestern Texas (southern Brewster and Presidio counties), and southwestern New Mexico, at elevations of about 500 to 3,000+ meters. Most occurrences in Mexico are at elevations of 1,000-2,200 meters, but this bat been captured at an elevation of 3,780 meters (Arita 1991), and the type specimen was caught near snow line at 17,816 feet (5,747 meters) on Mt. Orizaba, in Veracruz, Mexico (USFWS 2000). In Texas, the species is known from the Big Bend National Park and Chinati Mountain area. Two specimens of Leptonycteris taken in Hidalgo County, New Mexico (in 1963 and 1967), were determined to be L. nivalis. The presence of this species in New Mexico was reconfirmed in Hidalgo County in 1992 (Hoyt et al. 1994). This species formerly was thought to occupy a much larger area, extending into southern Mexico and Guatemala, but specimens collected from those areas have been assigned to L. yerbabuenae (Arita and Humphrey 1988). The only colonial roost in the U.S. is a cave at Emory Peak, at an elevation of 2,290 meters, in the Chisos Mountains, Texas. Simmons (2005) described the range of L. nivalis as extending to southern Mexico and Guatemala, and she also included southeastern Arizona in the range. However, no actual records for Arizona are known, and Arita (1991) showed the range as extending only as far south as Puebla and northern Guerrero.
Native:Guatemala; Mexico; United States
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||This bat is uncommon or rare (Reid, 1997). The number of occurrences or subpopulations is unknown but probably exceeds 20; Arita (1991) mapped a few dozen collection sites in Mexico. One known colonial roosting site exists in the United States, but there could a one or more additional sites that have not yet been detected. The number of occurences or subpopulations with good viability is unknown but likely there are not very many. Several caves in central Mexico were known to contain considerable numbers in the past but now contain only small colonies or none at all (see USFWS 2000). Probably declining in number of occurrences or subpopulation and in overall population size, but the rate of decline is unknown; better information is need.|
|Habitat and Ecology:||
This species can be found in pine-oak and deciduous forest and desert scrub (Reid, 1997). This species usually favors higher and cooler regions than L. yerbabuenae (Arita, 1991). It usually roosts in large groups (up to 10,000) in caves or mines; occasionally found in buildings, hollow trees, or culverts. Emerges well after sunset and feeds on pollen and nectar, principally of agaves and various cacti. Bombax, Ceiba, Ipomoea, Calliandra, Pinus, and grasses are also important food sources in Central Mexico (Gardner, 1977). Fruit and insects are sometimes taken. Northern populations migrate south in winter; numbers found in caves fluctuate greatly from year to year, indicating eruptive movements in addition to seasonal migration. Single young are born in May or June (Hensley and Wilkins, 1988; Reid, 1997).
Single known U.S. roost at Emory Peak (Texas): 10,650 bats in 1967, 5,000 in 1968, 3,900 in 1969, 0 in 1970, 8025 in 1971, 1000 in 1983, 4,942 -5,990 in 1988, 5,000+ in 1991, 0 in 1992, and 2,859 in 1993 (Matthews and Moseley 1990, see USFWS 2000); number fluctuates widely from one year to the next; fluctuation may be in part due to some counts being made before or after the main period of bat occupation of the cave (Cockrum and Petryszyn 1991). Texas population may be a "spill-over" colony present during years of high population or reduced food supply. See Arita (1993) for general information on conservation status and population size in Mexico. Reliable estimates for Mexican populations are not available, but Arita and Prado rated this species as widespread and scarce in Mexico.
Long-term trend is unclear. Extent of occurrence and area of occupancy probably have not changed much, but the number of occurrence or subpopulations and population size may have dramatically decreased in some locations during the last three decades. Wilson et al. (1985) found that this species was either completely absent or present in reduced numbers in known roosts. The number of bats found represented only a fraction of the total reported in previous studies. For example, in an abandoned mine in Nuevo Leon, Mexico, where an estimated population of 10,000 was observed in 1938, no individuals of L. nivalis were found in 1983 (Wilson 1985). Another mine in Nuevo Leon had a ceiling covered with newborn bats in 1967, but only one bat was found in 1983. A few other roosts had reduced numbers of bats compared to findings during previous surveys. These changes could indicate a decline in the overall population, but they might reflect movement of bats among different roosting sites in different years, or they could result from seasonal changes in bat distribution (survey dates varied).
Abundance at one of the two known roosting sites in the United States (a cave in Big Bend National Park) fluctuates widely from year to year (0 to 10,000+ individuals). No significant trend can be ascertained from these data, which are the best available for the species. Reasons for the fluctuations are not understood, but they could reflect annual variations in food resources in different parts of the range (USFWS 2000).
Habitats include desert scrub, open conifer-oak woodlands, and pine forests in the Upper Sonoran and Transition Life Zones, generally arid areas where agave plants are present (USFWS 2000). Colonies roost in caves (or similar mines and tunnels), sometimes in culverts, hollow trees, or unused buildings. Roosting habitat requirements are not well known.
|Major Threat(s):||Primary threats include disturbance of roosts, loss of food sources through clearing of land for agriculture and human exploitation of agaves (e.g., for production of alcoholic beverages), and direct killing by humans. Other threats may include negative effects of ingestion of pesticides applied to plants, competition for roosts and nectar, natural catastrophes, disease, and predation; however, these are not believed to be major limiting factors, though some of them could become significant for populations reduced to small size by other factors (see USFWS 2000). These bats are sensitive to disturbance in their roosting sites (they often quickly take flight upon human entry; Wilson 1985, Wilson et al. 1985) and, in general, roosting caves are becoming increasingly subject to human destruction and disturbance. Human disturbance and destruction of roost sites is a common occurrence in Mexico. The availability of roost sites free from disturbance may be a significant limiting factor. Special precautions should be taken when mine and cave surveys are conducted. In June and July when the young are very small, disturbance can cause them to lose their grasp on the rock and fall to their death. During hibernation, disturbance will cause an increase in metabolism; this use of fat reserves may cause starvation prior to spring (New Mexico Department of Game and Fish 1996). A major problem for bats all over Mexico is that uninformed citizens frequently destroy all bats in a roost, believing them to be vampire bats. Foraging habitat can be degraded or destroyed by harvesting of agave (an important food resource). It has been estimated that bootleg mescal makers are eliminating between 500,00 and 1,200,000 wild paniculate agave a year in Sonora alone. Agave plant parts are harvested just before they bloom; this prevents flowering and can prevent reproduction by the affected plant (an agave plant grows for 10 to 20 years, flowers only once, then dies). However, there are few places in Sonora or elsewhere in Mexico where wild Agave harvesting has eliminated a significant percentage of nectar-producing genets, and plants harvested by indigenous people generally produce vegetative offshoots that may eventually produce flowers (Nabhan and Fleming 1993). Populations of unharvested plants persist in many areas that are not easily accessible to humans. The negative impact of agave harvest probably is not as great as was previously believed. On the other hand, reduced pollination resulting from decreased bat populations may eventually lead to a reduction in agave distribution and abundance. Some foraging habitat has been degraded or destroyed by expansion of agriculture and other land uses. Large areas of both the Sierra Madre Oriental and Sierra Madre Occidental and the Mexican Plateau have been converted to agriculture or rangeland. This species may experience predation from owls, hawks, snakes, and mammals, but natural levels of predation likely are inconsequential to the overall status of the species. However, increased populations of domestic and feral cats and other predators near human habitations may affect the survival of colonies, particularly maternity colonies (USFWS 2000).|
A protected population exists at Emory Peak, Big Bend National Park, Texas (USFWS 2000). Further regular surveys are needed to determine important roost sites, abundance, and trends. Conservation of this bat will require maintenance of relatively large areas of wild Agave. Identification and protection of currently and formerly occupied roost sites and protection of foraging habitat in at least several areas throughout the range are important conservation needs. Populations need to be defined, and movement patterns need to be better understood. Accurate censusing methods need to be developed.
In Mexico is listed as threatened under NOM - 059 - SEMARNAT - 2001, and is priority species of the Bat Conservation Program (Arroyo-Cabrales pers. comm.).
|Citation:||Arroyo-Cabrales, J., Miller, B., Reid, F., Cuarón, A.D. & de Grammont, P.C. 2008. Leptonycteris nivalis. The IUCN Red List of Threatened Species. Version 2014.3. <www.iucnredlist.org>. Downloaded on 21 April 2015.|