Fringed bat COSEWIC assessment and status report: chapter 5

Habitat

Habitat requirements

General

In the United States, the Fringed Bat ranges from sea level to 2,850 m above sea level where it occupies desert, steppe, oak and pinyon woodlands, coastal forest, and montane spruce-fir forest (O’Farrell and Studier 1980). In Canada, this species is restricted to grassland, shrub-steppe and open ponderosa pine forest where most occurrences are from 300 to 800 m elevation in the Bunchgrass, Ponderosa Pine, or Interior Douglas-fir biogeoclimatic zones (Meidinger and Pojar 1991).

Roosting habitat

Throughout most of its range this bat exploits a variety of roosting sites. Day roosts including maternity colonies are located in the attics of buildings, caves, tunnels, mines, and rock crevices (Easterla 1973; O’Farrell and Studier 1980; Cryan et al. 2001). Cryan et al. (2001) observed that cliff roosts tended to be situated on south-facing slopes, but no data have been recorded on the microclimate of caves and mines used as day roosts. Roosts in buildings are usually in dark attics with warm temperatures. Recent studies with radio-tracking in Arizona, California, New Mexico, and South Dakota have revealed that this species also roosts in trees (Chung-MacCoubrey 1996; Rabe et al. 1998; Weller and Zabel 2001; Cryan et al. 2001). It generally roosts under loose bark using large snags in decay classes 2 and 3 (dead trees with broken tops and bark remaining) or in live ponderosa pine (Pinus ponderosa) trees with long vertical cracks and loose bark. Night roosts (temporary roosting sites used after nocturnal feeding bouts) are located in buildings, caves, mines and under bridges (Albright 1959; Adam and Hayes 2000). In North Dakota and Oregon this bat has been found hibernating during winter in caves or mine adits (Martin and Hawks 1972; Perkins et al. 1990).

In Canada where no radio-tracking studies have been done, what little is known about the roosting biology of the Fringed Bat is derived from opportunistic finds or inferences from captures. There are only two confirmed maternity colonies--both were in the attics of buildings (Maslin 1938; Sarell and Haney 2000). Sarell and Haney (2000) captured pregnant and post-lactating females in the southern Okanagan Valley and assumed that the maternity colonies were in nearby cliffs. In the Chilcotin-Cariboo region, night roosts have been found in buildings and root cellars (A. Roberts pers. comm.). In the southern Okanagan valley a well-known night roost is located in the Suzie Mine. The mine is only occupied at night (000-300 hrs) by the Fringed Bat.

A habitat suitability map developed for the southern Okanagan and Similkameen valleys (Ministry of Environment, Lands and Parks 1998) indicates that roosting habitat in this region (Figure 4) is widespread. Given the paucity of data on this bat’s roosting biology in Canada, the validity of the model (Warman et al. 1998) is dubious. For example, the model includes wildlife trees (dead trees or snags) as a critical habitat component, but tree roosting has yet to be shown for this species in Canada. The model also fails to incorporate night roosts.

Figure 4. Habitat suitability map showing roosting and foraging habitat of the Fringed Bat (Myotis thysanodes) in the southern Okanagan and Similkameen valleys of British Columbia. From Habitat atlas for wildlife at risk: south Okanagan and lower Similkameen, Ministry of Environment, Lands and Parks, 1998.

Habitat suitability map showing roosting and foraging habitat of the Fringed Bat (Myotis thysanodes) in the southern Okanagan and Similkameen valleys of British Columbia

Foraging habitat

Data on the foraging habitat are largely anecdotal. In British Columbia, Collard et al. (1990) tracked 21 Fringed Bats captured at the Suzie Mine that were marked with temporary light tags. Most foraged in riparian habitat from 3 to 10 m above ground after being released. Firman et al. (1994) observed a single light-tagged individual foraging over the forest canopy and along the edge of a lake. Roberts and Roberts (1992, 1993), Holroyd et al. (1994), and Sarell and Haney (2000) all reported captures of the Fringed Bat in mist nets or harp traps set in riparian thickets or at the edge of waterbodies. These captures could reflect foraging or drinking activity.

A habitat suitability map developed for the southern Okanagan and Similkameen valleys (Ministry of Environment, Lands and Parks 1998) demonstrated that foraging habitat in this region is widespread and continuously distributed (Figure 4). According to the map, only urban and agricultural lands in the bottomlands lack suitable foraging habitat. Nevertheless, with so little known about the foraging biology of the Fringed Bat in Canada reliability of the habitat suitability model is unknown.

Trends

The valleys of the interior grasslands of British Columbia have been modified by live-stock grazing, irrigation, and local urban growth. Detailed analyses of habitat trends exist only for the southern Okanagan-Similkameen valleys. Natural communities in this region were first impacted by livestock grazing in the late 1880s, but agricultural development (Table 1) associated with orchards, irrigated hay fields, and vineyards that began in the early 1900s and more recent urban growth have resulted in significant declines in grassland, wetland, and riparian habitats (Cannings et al. 1987; Lea unpublished data; Ministry of Environment, Lands and Parks 1998). According to Redpath (1990) more than 90% of the land in the southern Okanagan-Similkameen has been altered from its 'normal' state.

Table 1. Historical changes in area (hectares) of natural and anthropogenic habitats in the southern Okanagan-Similkameen valleys of British Columbia. Based on unpublished data from Ted Lea, British Columbia Ministry of Water, Air, and Land Protection.
Habitat Type 1800s 1939 1995 2001
Antelope-Bush
9607
7046
4279
4093
Big Sagebrush
7243
5567
4369
4369
RiparianTable 1 notea
8679
4996
2957
2957
Urban Area
0
368
3567
3567
Cultivated Area
0
11482
18871
19057

With so little known about this species’ roosting requirements in Canada, the impacts of agricultural development, urbanization, or forest harvesting on roosting sites is unknown. Riparian or marshy areas have declined in parts of this bat’s Canadian range. For example, according to the Habitat atlas for wildlife at risk: south Okanagan and lower Similkameen (British Columbia Ministry of Environment, Lands and Parks 1998) about 85% of the valley bottom riparian habitat has disappeared. However, data supporting the Fringed Bat’s dependence on riparian habitats for foraging are weak.

Protection/ownership

Quantitative assessment of land tenure for Fringed Bat habitat exists only for the southern Okanagan and Similkameen valleys (Ministry of Environment, Lands and Parks 1998). The 1998 analysis estimated that only 8% of potential Fringed Bat habitat was protected in conservation land (Table 2); a significant portion of habitat was either in Indian Reserve land particularly the Inkaneep and Penticton Reserves or private land holdings. Data in Table 2 were calculated before the establishment of new protected areas (South Okanagan Grasslands, White Lake Grasslands) as part of the Provincial Protected Areas Strategy. These new protected areas support additional Spotted Bat habitat and probably increase the proportion of habitat in conservation land to about 10 to 15%.

Table 2. Land tenure for Fringed Bat (Myotis thysanodes) habitat in the southern Similkameen-Okanagan valleys of British Columbia. Taken from Habitat atlas for wildlife at risk: south Okanagan and lower Similkameen, Ministry of Environment, Lands and Parks 1998.
Tenure Area (ha) % Total Habitat Table 2 noteb
Conservation Land
12,716
8
Provincial Land
70,204
43
Indian Reserve
37,317
23
Private Land
43,734
26

Page details

Date modified: