Natalus mexicanus G. S. Miller 1902
Creators: name: Don E. Wilson
name: Russell A. Mittermeier
Publisher: name: Lynx Edicions
Year: 2019
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Mammalia
Chiroptera
Natalidae
Natalus
Natalus mexicanus

description: 9.
Mexican Funnel-eared Bat
Natalus mexicanus
French: Natalide du Mexique / German: Mexiko-Trichterohr / Spanish: Natalido mejicano
Other common names: Mexican Greater Funnel-eared Bat
Taxonomy. Natalus mexicanus G. S. Miller, 1902,
“Santa Anita, Lower [= Baja] Califor nia, Mexico.”
Subspecies saturatus has been described from eastern Mexico, but type population represents only localized extremes in size and color variation. Monotypic.
Distribution. From S Baja California Sur, Sonora, and C Nuevo Leén (Mexico) S to Panama; also on Pacific Is of Maria Magdalena (Mexico) and Coiba (Panama), and Caribbean Is of Cozumel (Mexico) and Providencia and San Andrés (Colombia).
Descriptive notes. Head—body 38-43 mm, tail 47-55 mm, ear 12-17 mm, forearm 35-1-40-6 mm (males) and 34-40-4 mm (females); weight 3-9-8 g (males) and 3-5-7 g (females). Pelage varies from very pale stramineous (yellowish gray) to rich chestnut brown, with dorsal hairs unicolored or bicolored and bases lighter than tips; ventral hairs are unicolored and usually lighter than dorsal hairs. There are dense mustachelike hair tufts along lateral margins of upper lip and on dorsum of muzzle. Medial ear margin is slightly concave; lateral ear margins are deeply concave; there are 5-6 ear pleats; pinna is funnel-shaped with markedly pointed tip. Natalid organ of male is relatively flat, elliptical to wedge-shaped, and extends onto crown. Wings attach to tibia above ankle; free margin of uropatagium has sparse fringe of thin hairs; ungual tufts are absent. Braincaseis inflated,rising gently from rostrum; premaxilla is not inflated; maxilla dorsal to molars is convex and not inflated; postorbital region of skull in dorsal view has sides widely diverging rostrally; palate is present between pterygoids; caudal margins of maxilla in ventral view form acute angle with longitudinal axis of skull; basisphenoid pits are shallow; mesostylar crest on third molar is absent.
Habitat. Wide variety of habitats from desert scrub to secondary rainforest and more commonly lowland mesic to dry forests from sea level to elevations of 2300 m —the largest elevational range of any species of natalid. Niche models indicate that optimal habitat for the Mexican Funnel-eared Bat is tropical deciduous and semideciduous forests, with mean annual temperatures of 22-26°C and mean annual precipitation of 800-1500 mm. It roosts mainly in caves but also occupies abandoned mines. Other roostsites have included hollow trees (only two records), drainage pipe under a road, and space below an overhanging rock. Most roost caves used by Mexican Funnel-eared Bats occur in limestone and range from very large (more than 10 km in linear extension) to very small (less than 10 m), and a few occur in volcanic rock or loose sandstone. They are usually found in warm (17-27°C) and humid (relative humidity 74-99%) caves and mines but avoid warmest parts of such refuges, staying in transition areas to hot passages.
Food and Feeding. There is no specific information available for this species, but the Mexican Funnel-eared Bat is certainly insectivorous.
Breeding. Reproduction of the Mexican Funnel-eared Bat has been well studied in northern Mexico and given the similarities with breeding patterns among Cuban funnel-eared bats, details described below probably hold true in more southern populations of the species. The Mexican Funnel-eared Bat has a single estrus per year and bears one young per year. Gestation is very long, with copulation and fertilization taking place in late autumn and early winter (December to early January when spermatogenesis peaks in males, and females begin to show implantation), and parturition taking place around mid-summer (late July). Testes size increases steadily from June (1 mm) to January (2 mm), with corresponding increases in sperm counts. Pregnant females carry a single embryo exclusively in the left horn of the uterus. In January-April, embryos weigh 0-01 g, have well-defined limb buds, but show little growth. In April-May, weight of embryos increases to 0-3 g, and limbs and wing membranes are well formed. From this point on, weight and forearm length of embryos grows exponentially until about c.1 month after birth. Young are born usually in the second one-half ofJuly; they are naked, have closed eyes, weigh 1-5-1-8 g, and have 11-16 mm long forearms. Immediately after birth, there is a fast growth spurt of ¢.145% increase in weight and ¢.185% increase in forearm length. Juveniles start flying in late August at end of the growth spurt in forearm length. After onset offlight, weight of young increases slowly but steadily until end of February when they are almost the same weight of adults (5:7-6-6 g). During this period, forearm length increases more slowly than weight but also attains a range (35-38 mm) near that of adults (36-39 mm). Body fur and open eyes start to be seen by mid-August c.2 weeks after birth. From August when the young begin to fly actively to November, pelage grows longer and paler from smoke gray to light grayish olive and becomes more strongly bicolored with mousegray hair tips. In a Mexican mine in late July, ¢.50 newborn Mexican Funnel-eared Bats were found in a cluster on the wall, c. 1 m from the floor and much closer to the entrance (c. 18 m) than areas where adults roosted (40-75 m away from entrance). When young begin to fly, some are still nursing, but others begin to consume insects. Neither sex seems sexually mature in their first year.
Activity patterns. Mexican Funnel-eared Bats are nocturnal. Nocturnal emergence begins at ¢.30 minutes after sunset and foraging 10-15 minutes before total darkness, with exoduslasting ¢.10 minutes. Individuals begin returning to roosts c¢.2 hours after emergence and continue entering and leaving roosts for the remainder of the night. Before emergence, most individuals in a colony hang near the entrance of the roost in a restless state, and if disturbed, some fly out and hang in vegetation outside until it becomes dark. While foraging, Mexican Funnel-eared Bats visit sources of drinking water. Flight is slow and very maneuverable, and individuals rarely get caught in mist nets. Even if they hit a mist net, they rarely become entangled and are able to fly off. Echolocation calls of the Mexican Funnel-eared Bat are very weak (low intensity) and hard to detect unless an individual is 0-5 m from the microphone. Current echolocation call detection techniques are barely suited for detecting low-intensity calls of Mexican Funnel-eared Bats during foraging. Calls recorded from captive individuals consist of short (c.2 millisecond) frequency-modulated (FM) sweeps, with most energy in second harmonic at 100-130 kHz, and are emitted at short and variable intervals. While roosting, individuals can be extremely still, allowing hand capture, but sometimes they fly away at the slightest indication of human presence. The Mexican Funnel-eared Bat is very susceptible to dehydration. Bats taken from humid interiors of a roost (84% relative humidity) to the exterior (65% relative humidity) can die within an hour, even though sheltered from the sun. Torpid Mexican Funnel-eared Bats have been found in a cave in northern Mexico when outside temperature was 12°C.
Movements, Home range and Social organization. Colonies of the Mexican Funneleared Bat switch between alternative roostsites, sometimes seasonally but also sometimes daily. In Mexico, number of individuals in one roost increased from less than ten to 300 individuals in a week and in another roost decreased from c. 1000 in winter to ¢. 200 in summer. Switching of roosts has been found to coincide with late pregnancy, lactation, and occupation of the cave by larger bat species. As in other species of funnel-eared bats, the Mexican Funnel-eared Bat probably has small home ranges due to its slow flight and high susceptibility to dehydration outside its roosts. It has been found sharing roosts with 32 other bat species but generally forms groups separated from other species. It mostly uses walls as roost perches but occasionally ceilings.
Status and Conservation. Classified as Least Concern on The IUCN Red List. The Mexican Funnel-eared Bat is the most common species of funnel-eared bat in museum collections, being known from 253 localities and represented by at least 2491 specimens. Number of specimens per locality is more evenly distributed relative to that of other species, with colony sizes ranging from a few hundred up ¢.1000 bats. Its abundance and wide distribution indicate that its threat level is probably the lowest of all species of funnel-eared bats.
Bibliography. Alvarez (1963), Anderson (1972), Avila & Medellin (2004), Baker & Greer (1962), Broadbooks (1961), Goodwin (1934, 1969), Hall & Dalquest (1963), Lopez-Wilchis et al. (2012), McNab (1969), Miller (2004), Mitchell (1965), Moreno (1996), Nowak (1994), Reid (1997), Rydell et al. (2002), Tejedor (2005, 2011), Villa (1967), Wang et al. (2003).
description: Published as part of Don E. Wilson & Russell A. Mittermeier, 2019, Natalidae, pp. 589-596 in Handbook of the Mammals of the World – Volume 9 Bats, Barcelona :Lynx Edicions on pages 594-595, DOI: 10.5281/zenodo.6811090