Fringed Myotis (Myotis thysanodes) Potential Occurrence: Unlikely to Occur

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Mammalia (Mammals): Chiroptera, Vespertillionidae

Fringed Myotis (Myotis thysanodes)

Potential Occurrence: Unlikely to Occur


Federal: None

State: None

Other: G4G5 S4 BLM:S

Photo: New Mexico Energy
pecies Description:

Unlike all other Myotis species in North America, M. thysanodes has a conspicuous fringe of hair along the posterior border of the interfemoral membrane that extends 1.0 to 1.5 mm beyond the uropatagium (Jones and Genoways 1967)…There appears to be geographic variation in fur color, with darker animals occurring in the northern portions of the species’ range (Miller and Allen 1928 in O’Farrell and Studier 1980). The dorsal fur varies in color from yellowish brown to dark brown with olive tones (O’Farrell and Studier 1980) or reddish tones (Barbour and Davis 1969). The ventral fur is usually somewhat paler and can be touched with ochre (Barbour and Davis 1969), but there may not be much color difference between the dorsal and ventral surfaces (O’Farrell and Studier 1980). (From Keinath 2004)


The fringed myotis is widespread in California, occurring in all but the Central Valley and Colorado and Mojave deserts. Its abundance appears to be irregular; it may be common locally. It occurs in a wide variety of habitats; records range in elevation from sea level to 2850 m (9350 ft in New Mexico) (Barbour and Davis 1969). Optimal habitats are pinyon-juniper, valley foothill hardwood and hardwood-conifer, generally at 1300-2200 m (4000-7000 ft). (From Harris 1990)

There are three recognized and one uncertain subspecies of Myotis thysanodes. Myotis thysanodes thysanodes occurs in the main part of the species’ range, M. t. aztecus occurs in Oaxaca, Mexico (Wilson and Ruff 1999), and M. t. pahasapensis occurs only in the Black Hills of South Dakota, Wyoming, and Nebraska (Bole 1935, Jones and Genoways 1967, Barbour and Davis 1969). According to Jones and Genoways (1967), M. t. pahasapensis has slightly larger ears (average 18.7 mm versus 16.2 mm in M. t. thysanodes), a shorter forearm (41.1 mm versus 43.0 mm), a smaller skull (see measurements in Jones and Genoways 1967), and darker ears and membranes that contrast in color with the dorsal pelage. While not universally recognized as a valid subspecies, M. t. vespertinus has been suggested to occur west of the Cascade Mountains, along the Pacific coast, from southwestern Washington south through Oregon and into northwestern California as far south as Humboldt and Shasta counties (Manning and Jones 1988). (From Keinath 2004)

Life History & Threats:

The fringed myotis roosts in caves, mines, buildings, and crevices. Separate day and night roosts may be used. Adults and subadults generally form separate groups in the roost. Maternity colonies of up to 200 individuals are located in caves, mines, buildings, or crevices. Adult males are absent from maternity colonies, which are occupied from late April through September. Maternity group members may remain together during hibernation. Nocturnal. Hibernates. This species is active from shortly after sunset to 4-5 hr after sunset. Most activity is from 1-2 hr after sunset. Wind and precipitation reduce activity. The period of hibernation lasts from October through March. Pregnant and lactating females may be heterothermic as an energy saving strategy (Studier et al. 1973). This species is migratory, making relatively short, local movements to suitable hibernacula. Probably not territorial. May be found singly or in colonies. Mating occurs in the fall, followed by delayed fertilization. Gestation lasts 50-60 days. The young are born from May through July, but most are born in late June. A single offspring is produced per yr. Lactating females are found in July and August. Young females are mature in their first yr, males are mature in their second yr. The maximum longevity recorded is 18.3 yr (Tuttle and Stevenson 1982). Sympatric with many other species. This species is a slow, maneuverable flier, and uses foliage gleaning. Possible predators include owls and snakes. (From Harris 2000)

Myotis thysanodes, like many bat species, is very sensitive to disturbance at or modification of roosts and the surrounding environment. The most important roosts are maternity colonies and hibernacula. Disturbance of roosts (i.e., caves, mines, cliffs, buildings, snags; see Roost section) can take the form of direct human contact or alteration of the roost environment. Roost destruction has been caused by anthropogenic activities including removal of large-diameter, cavity-forming trees suitable for roosting and modification of the forest structure around roost sites. Other important impacts include human activity in caves, closure of mines without consideration of bat access, and uninformed building and bridge modification. (From Keinath 2004)

Habitat & Habitat Associations:

General Habitat:

Myotis thysanodes appear to use a fairly broad range of habitats (Cryan 1997). The most common habitats in which this species has been found are oak, pinyon, and juniper woodlands or ponderosa pine forest at middle elevations (Davis 1966, Barbour and Davis 1969, O’Farrell and Studier 1980, Cockrum et al. 1996, Wilson and Ruff 1999, Ellison et al. 2004). They also appear to use deserts (Cockrum et al. 1996), grasslands, and other types of woodlands. When trying to generalize all published information, one observes that M. thysanodes is mostly found in dry habitats where open areas (e.g., grasslands and deserts) are interspersed with mature forests (usually ponderosa pine, pinyon-juniper, or oak), creating complex mosaics with ample edges and abundant snags. This can take a variety of forms in Region 2, where open areas are likely represented by short and mixed-grass prairie, sagebrush and other xeric shrublands and forests, including a variety of low and mid-elevation pine and mixed-conifer types, some not adequately studied in other areas (e.g., lodgepole pine and Douglas-fir in addition to ponderosa and pinyon-juniper). (From Keinath 2004)

The best habitat model for predicting bat presence in an area contained only these variables (the number of snags ≥ 30 cm DBH combined and percent canopy cover), where increasing numbers of snags and decreasing canopy cover increased the probability of bat occurrence (Weller 2000). Abundance of large snags and low canopy cover allows more thermal heating of roosts, easier flight access to roosts, and the ability to readily switch roosts in the event of roost collapse, for predator avoidance, or to find more suitable microclimates (Kunz 1982, Lewis 1995, Weller 2000). In such circumstances, Myotis thysanodes have been known to switch roosts several times a week (e.g., every 1.72 ± 0.23 days; Weller and Zabel 1999). (From Keinath 2004)

Although found in a variety of habitats, Myotis thysanodes appears to have a lower urine concentrating ability than most bats (Geluso 1980), suggesting a predisposition to more mesic environments or environments where persistent sources of drinking water are readily available. Dependence on nearby water sources is also supported by the fact that roost sites have been shown to be located closer to stream channels than expected by chance (Weller and Zabel 2001)… Smaller bats, such as Myotis thysanodes, can be seen at a wider variety of water bodies, because they need a minimal swoop zone and can maneuver through vegetative clutter. Such species can regularly use water sources as small as cattle stock tanks (Herder 1998) or persistent forest seeps. (From Keinath 2004)

Myotis thysanodes appear to range in elevation between roughly 1,200 and 2,100 m, and they can be found up to 2,850 m in spruce-fir forest in New Mexico (Barbour and Davis 1969, Arizona Game and Fish Department 1997). A similar elevation range of 1,340 to 1,890 m was reported for M. t. thysanodes in Arizona (Agyagos et al. 1994). They have occasionally been reported from elevations of less than 150 m in coastal areas of California (Orr 1956), including at sea level on San Clemente Island off the southern coast of California (Von Bloeker 1967, Brown 1980). (From Keinath 2004)

Foraging Habitat:

Many species of bats, including Myotis thysanodes, forage over bodies of water, as insect abundance (e.g., mosquitoes) is often much greater in these areas (Thomas and West 1991 as cited in Christy and West 1993, Grindal et al. 1999). Also, it has been shown that many bats preferentially forage along forest or field edges (Furlonger et al. 1987, Fenton 1990, Grindal 1995, Ellison et al. 2004). This makes ecological sense because forests and forest edges have been shown to support more insect biomass, abundance, and richness than adjacent open areas (Lewis 1970, Grindal 1995, Grindal and Brigham 1999), while edges have low spatial complexity relative to interior forest. (From Keinath 2004)

Roosts, Hibernacula, and Nurseries:

In northern California it appears that male and female Myotis thysanodes use tree snags exclusively for day roosts (Weller and Zabel 2001). In areas where tree roosting is the norm, vegetative structural complexity of habitat around roost sites is likely more important than plant species composition or general topographic features in determining local distribution. Myotis thysanodes in the Weller and Zabel study chose roost areas with a higher density of large snags (i.e., 8.3 ± 0.8 snags ≥ 30 cm diameter at breast height per 0.1 ha) than surrounding forest (2.9 ± 0.3 per 0.1 ha; P = 0.002) and lower canopy cover (78.5 ± 2.6 percent) than surrounding forest (89.2 ± 1.1 percent; P = 0.004), which are likely correlated variables. Thus, as in studies of other tree roosting bats, it appears that M. thysanodes roost trees are in open microsites in otherwise contiguous forests, not in the open (Vanhof 1995). (From Keinath 2004)

Roost snags also tended to be taller relative to the surrounding canopy than random snags, had a higher diameter at breast height than random snags, and were nearer to stream channels than randomly selected points. Since M. thysanodes tended to roost under loose bark, most roost snags were in decay classes 2 to 4 (Thomas et al. 1979). Roost snags were Douglas-fir, ponderosa pine, and sugar pine used in approximate proportion to their availability (the largest snags in the study area were predominantly Douglas-fir). (From Keinath 2004)

Few hibernacula have been well documented, but those that have are generally cool and usually in caves or mines with little temperature fluctuation throughout the winter, facilitating hibernation at a uniformly low metabolic rate… They have also been discovered hibernating in buildings and mines along the coast range north of San Francisco Bay (Pierson 1998). (From Keinath 2004)

Conceptual Basis for GIS Model Development: We mapped potential habitat for this species as:

General Habitat: all habitats in the Study Area (i.e., grassland, shrubland, woodland, and forests)

Roosts & Hibernacula:

  • cismontane, broadleaf upland, coniferous forests, or riparian woodland/forest with > 30 cm DBH and contiguous canopy cover (> 40%).

  • Abandoned buildings

Note that caves and snags have not been mapped on the Preserve.

Foraging Habitat:

  • permanent or intermittent watercourses, ponds

  • habitat edges: edges of grasslands (all types), chaparral (all types), woodland/forests (all types), and riparian woodland/forests (all types).

Potential Occurrence in the Galbreath Wildlands Preserve:

Habitat: Fringed Myotis occupy a wide variety of habitats, but mostly occur in areas that have complex mosaics of mature forest and open habitats. They are dependent on:

  • nearby water for drinking,

  • snags located in open microsites of dense mature forests for roosting (in northern California, they use snags exclusively for day roosts), and

  • open water and habitat edges for foraging.

In areas where they occur, their presence can be best predicted by high snag abundance and low canopy cover.

Habitat quality in the Preserve is poor to moderate. Surface water is available year round at ponds and tributaries to Rancheria Creek, and snags are relatively abundant on the Preserve. (Logging was discontinued in 2000). However, edge habitats used for foraging are not common within Preserve boundaries (Figure 107). In addition, the Preserve lies at lower elevational range for this species. In Arizona and New Mexico, they are usually found between 1200 and 2100 m (3900 to 6900 ft), but in California, they have been occasionally reported in coastal areas at the elevation of the Preserve.

Nearest Occurrence:

Documented Occurrences in Preserve: This species has not been documented in the Preserve. To our knowledge, no surveys have been conducted.

Nearest Occurrence to Preserve: Fringed Myotis has not been reported to occur in USGS quads adjacent to the Preserve.

Summary: We anticipate that Fringed Myotis are “Unlikely to Occur” in the Preserve. Habitat quality is poor to moderate and this species is usually found at much higher elevations.


Harris J. 2000. Fringed Myotis. California Wildlife Habitat Relationships System. . 2010 July 1.

Keinath D.A. 2004 October 29. Fringed Myotis (Myotis thysanodes): a technical conservation assessment. USDA Forest Service, Rocky Mountain Region. < /projects/scp/assessments/fringedmyotis.pdf>. 2010 July 1.
New Mexico Energy, Minerals and Natural Resources Department. Fringed Myotis Photo. Bats

in New Mexico. . 2010 June 16.

Species Account Description: Emily Harvey

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