Fringed bat COSEWIC assessment and status report: chapter 2

COSEWIC Executive Summary

Fringed Bat
Myotis thysanodes

Species information

The largest (mean forearm length= 42.3 mm, mean body mass 7.1 g) Myotis species in Canada, the Fringed Bat (Myotis thysanodes) has pale brown dorsal fur, blackish wing and tail membranes, and long black ears. The most distinctive feature of this species is a fringe of stiff hairs located on the trailing edge of the interfemoral membrane. M.thysanodesbelongs to the Order Chiroptera, Family Vespertilionidae. Among the North American long-eared Myotis species, M. thysanodes is the most morphologically distinct but it shares a close affinity with the Western Long-eared Myotis (Myotis evotis) and Miller's Myotis (Myotis milleri) in allozyme and chromosomal traits. Recent mtDNA analyses have shown that M. thysanodes is most closely related toM. evotis and in some regions there has been mitochondrial introgression between these two species. Although four subspecies are recognized, the subspecies taxonomy is not supported by mtDNA analysis.

Distribution

The Fringed Bat ranges throughout western North America from Chiapas and Veracruz, Mexico, across much of the western United States to southern British Columbia. A disjunct population inhabits the Black Hills of South Dakota and Wyoming. In Canada, this bat is restricted to the Okanagan, Similkameen, north and south Thompson, Fraser and Chilcotin River valleys of southern British Columbia. A specimen from Olympic National Park on the Olympic Peninsula identified as the Fringed Bat suggests that this species could inhabit coastal British Columbia. The 33 distributional records in Canada represent about 18 element occurrences. The area of occupancy is unknown; the extent of occurrence in Canada is about 8,650 km². This represents < 5% of the species' global range.

Habitat

In the United States, this species uses a variety of roosting sites for day and night roosts--buildings, caves, tunnels, mines, and rock crevices. In Canada where no radio-tracking studies have done, what little is known about the roosting biology of the Fringed Bat is derived from opportunistic finds or inferences from captures. The two confirmed maternity colonies in Canada were in the attics of buildings. M. thysanodes may also roost in cliff crevices and trees but this has not been confirmed. Night roosts are in buildings and abandoned mines. Little is known about its foraging habitat in Canada but anecdotal evidence suggests it may use forage in riparian habitats.

Biology

What is known about the biology of the species is based largely on studies done in the United States. Mating occurs sometime after this species leaves its maternity roost in late summer. Females arriving at the maternity colony in early April are carrying sperm in their uteri, but ovulation and fertilization occurs nearly a month later. Females give birth to a single young and produce only one litter in the breeding season. Females presumably breed in their first year, but males evidently do not breed until their second year.

When exposed to ambient temperatures ≤ 24°C, breeding females will use torpor or regulate their body temperature by increasing their metabolic rate. Energy demands are greatest for this species during lactation. Fringed Bats have been found hibernating in Oregon and North Dakota, but winter surveys of 18 caves and mines within the Canadian range found no hibernating Fringed Bats.

Radio tracking studies have shown that this bat generally occupies a limited area of about 4 km². Roosts in permanent structures such as buildings are generally occupied throughout the entire summer.  But Fringed Bats roosting in trees and rock crevices frequently switch their roosts, remaining at a roost site for only a few days. They rarely move more than 2 km between roosts. Nothing is known about migratory movements in the Canadian population.

The Fringed Bat eats mostly moths, beetles, flies, lacewings and some flightless invertebrates. The slow manoeuvrable flight and moderate to low intensity, frequency- modulated, echolocation calls suggest that it is adapted for gleaning, i.e., taking prey from surfaces.

The Fringed Bat is colonial. Maternity colonies in buildings may contain up to 1,000 to 1,200 individuals. Maternity colonies in tree or rock crevice roosts, however, are smaller, usually fewer than a few dozen animals. Although it often switches its day roosts, there appears to be some fidelity to a local area; night roosts may be used by the same individuals over a period of years.

Population sizes and trends

There are no population estimates for the Canadian population and no data exist to assess population trends. In various surveys done in British Columbia, the Fringed Bat is rarely captured in mist nets and harp traps in comparison to the 6 otherMyotis species found within its range. To what extent the few captures can be attributed to rarity or simply this species’ ability to avoid capture is unknown.

Limiting factors and threats

With so little known about this species’ biology in Canada, it is difficult to define any threats or limiting factors. Given this species’ diverse and flexible roosting habits in the United States, roosting habitat may not be limiting. Most of the threats are generic such as disturbance to maternity colonies in buildings, disturbance of night roosts in mines or other manmade structures, and the impact of pesticides on invertebrate prey.

Special significance of the species

The Fringed Bat is one of three western North American bat species confined to the intermontane grasslands of British Columbia in Canada. It is a member of a diverse temperate bat community of 12 to 14 species and the largest of the 7 Myotis species. Its precise niche in this community, however, is virtually unknown.

Existing protection or other status designations

The Fringed Bat was designated Special Concern by COSEWIC in 1988. The global heritage status rank is G4G5 (apparently secure to secure); national ranks are N4N5 (apparently secure to secure) for the United States and N2N3 (imperilled to vulnerable) for Canada. Three states (Idaho, Wyoming, Nebraska) rank the Fringed Bat as S1 or S1? (critically imperilled); two states (Oregon, South Dakota) rank this species as S2 (imperilled). Washington, Montana, Texas, and Utah rank the Fringed Bat as S3 (vulnerable). British Columbia has designated the Fringed Bat as S2S3 (imperilled to vulnerable). In British Columbia, the Fringed Bat is protected from killing under the provincial Wildlife Act, and it is listed as an Identified Wildlife Species under the revised British Columbia Provincial Forest and Range Practices Code. Nonetheless, the Forest and Range Practices Code only applies to provincial crown land; in the southern portion of the Canadian range, for example, nearly 50% of this species’ habitat is exempt from the code.

COSEWIC History

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal-Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. On June 5, 2003, the Species at Risk Act (SARA) was proclaimed. SARA establishes COSEWIC as an advisory body ensuring that species will continue to be assessed under a rigorous and independent scientific process.

COSEWIC Mandate

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assesses the national status of wild species, subspecies, varieties, or other designatable units that are considered to be at risk in Canada. Designations are made on native species and include the following taxonomic groups: mammals, birds, reptiles, amphibians, fishes, arthropods, molluscs, vascular plants, mosses, and lichens.

COSEWIC Membership

COSEWIC comprises members from each provincial and territorial government wildlife agency, four federal organizations (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biosystematic Partnership, chaired by the Canadian Museum of Nature), three nonjurisdictional members and the co-chairs of the species specialist and the Aboriginal Traditional Knowledge subcommittees. The committee meets to consider status reports on candidate species.

Definitions (after May 2004)

Species
Any indigenous species, subspecies, variety, or geographically or genetically distinct population of wild fauna and flora.

Extinct (X)
A species that no longer exists.

Extirpated (XT)
A species no longer existing in the wild in Canada, but occurring elsewhere.

Endangered (E)
A species facing imminent extirpation or extinction.

Threatened (T)
A species likely to become endangered if limiting factors are not reversed.

Special Concern (SC)Footnotea
A species that may become a threatened or an endangered species because of a combination of biological characteristics and identified threats.

Not at Risk (NAR)Footnoteb
A species that has been evaluated and found to be not at risk.

Data Deficient (DD)Footnotec
A species for which there is insufficient scientific information to support status designation.

 

Canadian Wildlife Service

The Canadian Wildlife Service, Environment Canada, provides full administrative and financial support to the COSEWIC Secretariat.

 

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