Spotted bat (Euderma maculatum) COSEWIC assessment and status report: chapter 5

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Habitat

Habitat requirements

General

In the United States, the Spotted Bat ranges to 3,230 m above sea level (Watkins 1977; Reynolds 1981) and it occupies habitats from desert to coniferous forest. In Canada, this species is restricted to grassland, shrub-steppe and open ponderosa pine (Pinus ponderosa) or Douglas-fir (Pseudotsuga menziesii) forest where most occurrences are from 300 to 900 m elevation in the Bunchgrass, Ponderosa Pine, or Interior Douglas-fir biogeoclimatic zones (Meidinger and Pojar 1991).

Roosting habitat

Known day roosts are in crevices suggesting that the Spotted Bat has specialized roosting requirements. Day roosts, including the maternity roosts where females give birth to their young, are located in the crevices or cracks (2.0 to 5.5 cm wide) of high cliff faces (Poché 1981, Leonard and Fenton 1983; Sarell and Haney 2000). In British Columbia, the Spotted Bat generally selects vertical faces up to 400 m high in cliffs (Figures 4, figure 55) or rocky outcrops of granitic gneiss, limestone or basalt (Roberts and Roberts 1993; Sarell and Haney 2000). These sites typically have warm aspects, but the specific physical features of roost sites selected by this bat are not known. Wai-Ping and Fenton (1987) found considerable variation in the height, length, and aspect of six cliffs used as day roosts in the southern Okanagan valley. Because they are inaccessible, no research has been done on the microclimate in these crevice roosts.

Figure 4. Vaseux Lake and McIntyre Bluff in the southern Okanagan Valley. The cliffs at McIntyre Bluff support as many as 30 roosting Spotted Bats (Euderma maculatum); marshy areas by the lake are important foraging habitat. Photo D. Nagorsen.

Following radio-tagged bats, Wai-Ping and Fenton (1989) found no evidence that this species uses night roosts (temporary roosting sites used after nocturnal feeding bouts) in the southern Okanagan Valley. However, in Grand Canyon National Park in northern Arizona three female Spotted Bats were found night roosting in aspen trees (Rabe et al. 1998). This is the only report of the Spotted Bat roosting in trees and using night roosts.

The winter roosting habitat is essentially unknown. Hardy (1941) reported four Spotted Bats hibernating in a cave in Utah, but his anecdotal observation is inconsistent with several comprehensive surveys of mines and caves in various parts of the range (e.g. Poché 1981; Kuenzi et al. 1999) that have shown no evidence for roosting in caves or mines.

A habitat model developed for the southern Okanagan and Similkameen valleys (Ministry of Environment, Lands and Parks 1998; Sarell and Haney 2000) was based on the presence of steep cliffs with horizontal or vertical crevices for roosting habitat. The habitat suitability map (Figure 6) demonstrates that roosting habitat in this region is fragmented and patchily distributed, a pattern consistent with the distribution of known roost sites described by Sarell and Haney (2000). Roosting habitat in the Thompson, Fraser and Chilcotin river valleys would be expected to show a similar pattern.

Figure 5. Chilcotin Oxbow, ChilcotinRiver.  Spotted Bats (Euderma maculatum) roost in the hoodoo formations and forage over adjacent riparian thickets. Photo T. Chatwin.

Foraging habitat

Monitoring echolocation calls and observations of radio-tagged individuals In Canada indicate that Spotted Bats forage over marshes, riparian habitats, open fields, and clearings in forest (Leonard and Fenton 1983; Wai-Ping and Fenton 1989, Holroyd et al. 1994). Open meadows appear to be important forging habitat for this species in parts of the United States (Storz 1995). This species also forages opportunistically as it commutes between its day roost and nocturnal foraging areas. Foraging sites are usually located within 6 km of cliff roosts and in close proximity to water (Collard et al. 1990). Of six habitats studied by Leonard and Fenton (1983) in the southern Okanagan Valley, foraging was observed in old fields and hay fields bordering ponderosa pine forest. Feeding buzzes (echolocation calls associated with prey capture) were detected in these habitats confirming that Spotted Bats were capturing prey. Foraging activity was low in burned and mature ponderosa pine forest and river side habitats. Because no feeding buzzes were detected, it appears that Spotted Bats were commuting through these habitats. No Spotted Bat activity was detected by Leonard and Fenton (1983) in a cherry orchard. Furthermore, these bats showed no evidence of foraging among groups of insects that concentrate at street or yard lights (Fenton pers. comm.). Another foraging study in the southern Okanagan by Wai-Ping and Fenton (1989) demonstrated similar results, although high foraging activity was also observed over marshy areas and open ponderosa pine forest woodland. In the Chilcotin River valley at the northern edge of the range, Spotted Bats forage in riparian habitats and open upland habitats with Douglas-fir.

Figure 6. Habitat suitability map showing day roosting and foraging habitat of the Spotted Bat (Euderma maculatum) 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.

A habitat suitability map developed for the southern Okanagan and Similkameen valleys (Ministry of Environment, Lands and Parks 1998; Sarell and Haney 2000) demonstrated that foraging habitat in this region is widespread and continuously distributed (Figure 6).

Trends

The valleys of the interior grasslands of British Columbia have been modified by livestock 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 a significant decline 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.

¹ water birch, cottonwood communities

The impacts of agricultural development and urbanization on Spotted Bat roosting habitat are minimal. Because rock faces and cliffs used by this bat are inaccessible and have little resource potential, they have been buffered from historical habitat changes. Garcia et al. (1995) concluded that there has been a "severe" reduction in foraging habitat citing "urbanization, destruction of wetlands, extensive irrigation, and the development of orchards, crop lands, and pasture". Nevertheless it is difficult to quantify the loss of Spotted Bat foraging habitat. Natural foraging habitats such as riparian or marshy areas have undoubtedly declined. 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. Nevertheless, anthropogenic habitats such as old fields, hay fields and golf courses provide significant feeding areas for the Spotted Bat (Leonard and Fenton 1983; Gitzen et al. 2001).

Protection/ownership

Quantitative data on land tenure for Spotted Bat habitat exists only for the southern Okanagan and Similkameen valleys (Ministry of Environment, Lands and Parks 1998). The 1998 analysis estimated that only 5% of potential Spotted 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%.

¹ includes roosting and foraging habitat