Natalus stramineus
Mexican funnel-eared bat

Mexican funnel-eared bats, Natalus stamineus, are confined to the Neotropics. They are distributed from Sonora and Nuevo Leon, Mexico, through Central America to Eastern Brazil. They can be found on the Yucatan Peninsula. Their distribution is patchy from Honduras to Panama. The species has also been seen in the Lesser Antilles, Hispaniola, and Jamaica. (Reid, 1997)

Mexican funnel-eared bats are generally found in dry and semi-deciduous forest and secondary growth forests, and are occasionaly found in evergreen forest. They can be found at elevations up to 2,400 m, but are usually found around 300 m. They roost in moist caves. (Reid, 1997)

Natalus stamineus is a very small, delicate, long-winged bat, ranging in weight from 3 to 5 g. Head and body length of Mexican funnel-eared bats is 38 to 46 mm; the tail length is from 47 to 52 mm; the length of hind foot is 8 to 9 mm; the length of the ear is 14 to 16 mm; the length of forearm is 36 to 39 mm. The sexes are similar in size. (Eisenberg and Redford, 1999; Eisenberg, 1989; Emmons, 1990; Reid, 1997; Silva , 1979)

The upper parts of this species are pale orange-brown or yellowish, with their under parts being yellow. The funnel-shaped ears are broad and cream colored, with black edges. The ears are angled forward. The species possesses very small eyes. Their faces are triangular, with pale pink skin and a mustache over the sides of their mouth. (Eisenberg and Redford, 1999; Eisenberg, 1989; Reid, 1997; Silva , 1979)

Adult male Mexican funnel-eared bats have a gland-like structure in the center of their foreheads known as the natalid organ. This gland is thought to be found only in the Natalidae, but there is not much known about its function. (Eisenberg and Redford, 1999; Eisenberg, 1989; Emmons, 1990; Reid, 1997; Silva , 1979)

The tail is long and completely enclosed in the interfemoral membrane. The tail is longer than the head and body length. This characteristic is unique to N. stramineus. The membrane is pale brown in color, with the edge fringed with short hair. The legs, tail, and arm bones are pink, contrasting with the brown membrane. The thumb is short and is almost enveloped in the antebrachial membrane, and the third phalanx of the third finger remains cartilaginous even in the adult. The wings are long and narrow. (Eisenberg and Redford, 1999; Eisenberg, 1989; Reid, 1997; Silva , 1979)

The dental formula is 2/3 1/1 3/3 3/3=38. (Eisenberg and Redford, 1999; Eisenberg, 1989; Reid, 1997; Silva , 1979)

Little is known about mating systems in this family. (Reid, 1997)

In El Salvador and Mexico, N. stramineus is reported to breed during the dry season. In Mexico and Central America, pregnant females have been found from January through July, and gestation is thought to last 8 to 10 months. Females are thought to be monoestrus, and to have slow development of the fetus. A single offspring is produced annually, weighing almost half of the adult mass, or about 2.1 g. (Nowak, 1999)

During the breeding season, the sexes apparently segregate, so that males and females roost separately. (Nowak, 1999; Reid, 1997)

Information on parental care of this species is not available. However, in other similar bats, females care for the young in the maternity roost, providing them with milk and grooming. Mothers are able to locate their own young among the many little bats present. Since males roost separately from females during rearing of the offspring, it is certain that males do not play a role in parental care. (Nowak, 1999)

Information on the longevity of this species is not available. However, in general, microchiroptera are long-lived animals. Some species of similar small size are known to live as many as 20 years. (Nowak, 1999)

This species generally roosts in deep, moist caves. These bats are typically found in groups of up to 300 bats in one colony. While roosting in the caves, the individuals are spaced out widely in the dark caverns. Most flight occurs at understory level, with great speed and agility in dipping, twisting, and dodging the vegetation. These bats are most active within 2 hours after sunset. As the evening progresses, the bats may use nighttime refugia which differ from their normal daily roosting location. Northern populations will sometimes migrate, causing colony size to vary considerably. (Reid, 1997)

The home range size for these animals has not been reported.

These bats find their prey through echolocation. The means of communication used with conspecifics has not been detailed in the literature, however, it is likely that N. stamineus is like other small microchiroptera with regard to communication. Most bats use vocal signals when communicating with one another. Some tactile communication occurs in the roost, especially between mothers and their offspring. Scent cues are probably used, as evidenced by the ability of a mother to distinguish her offspring from amid the hundreds of young bats in a maternity roost. (Eisenberg, 1989; Nowak, 1999)

Groups of Mexican funnel-eared bats leave the roost approximately 30 minutes after sunset to feed on small, flying insects. They find these insects by using high frequency ultra sounds up to 170 kHZ. (Reid, 1997)

No information on predation on this species was found. Because these animals fly and don't land in places easily accessible to many predators, it is likely that they are not a significant food source for predator populations. Some owls might take these bats in flight. Other predators would have to either find them in their roost, or catch them going into or coming out of the roost.

Mexican funnel-eared bats feed on large quantities of insects, undoubtedly affecting insect populations. (Reid, 1997)

Mexican funnel-eared bats feed on large quantites of insects that may be crop pests or carry human disease. (Reid, 1997)

It is unlikely that these animals have a negative affect on human economies.

Mexican funnel-eared bats are not listed by IUCN or CITES. (Reid, 1997)