Myotis thysanodes G. S. Miller 1897
Order Chiroptera : Family Vespertilionidae
DESCRIPTION. A relatively large Myotis with large ears and a distinct fringe of short, stiff hairs on free edge of the membrane between hind legs; tail from 75% to 81% of length of head and body; foot from 50% to 75% of length of tibia; ears projecting about 5 mm beyond snout when laid forward; pelage full and about 9 mm long on the back; upperparts uniform warm buff, tips of hairs shiny, bases fuscous black; underparts dull whitish. Dental formula: I 2/3, C 1/1, Pm 3/3, M 3/3 × 2 = 38. Averages for external measurements: total length, 86 mm; tail, 35 mm; foot, 9 mm; ear, 16.5 mm; forearm, 43 mm. Weight, 6–11 g.
DISTRIBUTION. This is a western bat known from Texas in the Trans-Pecos region in summer, where it has been collected at numerous localities. Two specimens have been captured from northWest Texas (Crosby County), but they were probably seasonal migrants. The fringed myotis has been captured in habitats ranging from mountainous pine, oak, and pinyon–juniper to desert scrub but seems to prefer grassland areas at intermediate elevations. No winter records are available for this bat in Texas, and its winter habits remain unknown.
SUBSPECIES. Myotis t. thysanodes.
HABITS. These bats roost in caves, mine tunnels, rock crevices, and old buildings in colonies
that may number several hundred. This is a highly migratory bat that arrives in Trans-Pecos
Texas by May, at which time it forms nursery colonies. This is a colonial bat, and
maternity roosts may contain several hundred individuals. The colonies begin to disperse
in October, and the winter locales and habits of this bat remain a mystery.
This species appears late in the evening to forage. They fly slowly and are highly maneuverable, allowing the bats to forage close to the vegetative canopy or about the face of small cliffs. No data are available on their specific food habits in Texas, but specimens from New Mexico contained mostly small beetles.
Its reproductive biology in Texas is poorly known. Unlike other species of Myotis, it appears that copulation, fertilization, and ovulation occur in the spring. In the Trans-Pecos, the date of parturition appears to vary greatly even within a colony. Juveniles have been observed at various stages of development (newly born pups to volant juveniles) on 10 July within a single maternity colony in Big Bend National Park. Congruently, lactating females have been captured in the park as early as 12 May. Apparently over a period of several weeks from mid-May to early July, gravid females give birth to a single fetus following a gestation period of 50–60 days. Immature individuals have been found in July and August in colonies of adult females. The young are able to fly at 16–17 days of age. As with other species of Myotis, adult males and females do not associate with each other in summer.
POPULATION STATUS. Common, spring–summer–fall resident. The fringed myotis is one of the most common bats in the Trans-Pecos region of Texas, and there are no known threats to its existence at this time.
CONSERVATION STATUS. The IUCN status of the fringed myotis is least concern because of its wide distribution, apparently stable population, and occurrence in a number of protected areas. It does not appear on the federal or state lists of concerned species.
From The Mammals of Texas, Seventh Edition by David J. Schmidly and Robert D. Bradley, copyright © 1994, 2004, 2016. Courtesy of the University of Texas Press.