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«*Healthy Little brown myotis in flight *Little brown myotis carcasses in Aelous Cave, VT in 2009 Credit: M. Brock Fenton Credit: Jonathan D. ...»

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*Healthy Little brown myotis in flight *Little brown myotis carcasses in Aelous Cave, VT in 2009 Credit: M. Brock Fenton Credit: Jonathan D. Reichard, Boston University’s CECB

Status Review Conducted by:

Thomas H. Kunz, Ph.D Jonathan D. Reichard, Ph.D.

Boston University’s Center for Ecology and Conservation Biology

In collaboration with:

Friends of Blackwater Canyon Wildlife Advocacy Project Bat Conservation International Center for Biological Diversity Meyer Glitzenstein & Crystal




A.  Taxonomy

B.  Description

C.  Distribution

D.  Habitat

1.  Winter Habitat/Hibernacula

2.  Spring, Summer, and Fall Habitat

E.  Foraging

F.  Reproduction

G.  Hibernation


A.  Core Range of the Species

B.  Status




A.  Disease or Predation

1.  Origin, Cause, History, and Rapid Spread of WNS

2.   Pathology of Geomyces destructans on Little Brown Myotis

3.  Prediction of Population Collapse and the Necessary Federal Response.................. 16  B.  Present or Threatened Destruction, Modification, or Curtailment of Habitat............... 17  C.  Other Natural or Manmade Factors affecting its Continued Existence

D.  The Inadequacy of Existing Regulatory Mechanisms









The little brown myotis (Myotis lucifugus) was once considered a common bat species because of its wide distribution, conspicuous maternity colonies, and relatively stable population status. However, emerging evidence recently published in one of the world’s leading peerreviewed scientific journals, Science, conclusively demonstrates that the species is in sharp decline due to the rapidly spreading white-nose syndrome (WNS) that has already resulted in several local extirpations and that is ultimately expected to cause regional and likely rangewide extinction of the little brown myotis in a very short ecological time frame (Frick et al. 2010b).

Specifically, this paper projects that regional species extinction will likely occur, with 99% certainty, in or before 2026 (Frick et al. 2010b) – eliminating at least the core northeastern range of the species, which clearly constitutes a significant portion of the species’ range in terms of population numbers, geographical distribution, resiliency, and habitat composition. The emerging science paints a grim picture of a once-healthy population being driven to extinction in a precipitous and unprecedented manner.

In light of the need for an immediate response to the WNS crisis, we have conducted this status review to analyze the best available scientific evidence regarding the continued viability of the little brown myotis in its core northeastern range and throughout its entire range in North America, in light of a continental-scale pandemic. Based on the study referenced above and other available data on WNS and its effects on the little brown myotis, we have concluded in this status review that extinction is virtually certain to occur in the core range of this species by 2026, and rangewide extinction may very well follow based on known and predicted infection dynamics of WNS.

Accordingly, this status review concludes, after applying the best available science to the legal and regulatory requirements of the Endangered Species Act (“ESA”), 16 U.S.C. §§ 1531that an endangered listing is warranted because the species is in imminent danger of extinction throughout a critical and significant portion of its range (the northeastern U.S), and is likely in danger of extinction throughout its entire range. Id. § 1533(a)(1). In addition, because of the immediacy and magnitude of the exigent WNS threat posed to the little brown myotis, this pandemic argues in favor of an emergency listing under the ESA while the U.S. Fish and Wildlife Service (FWS or Service) conducts its own species status assessment. Id. § 1533(b)(7).

–  –  –

A. Taxonomy The little brown myotis is a member of the Mammalian order Chiroptera, family Vespertilionidae, genus and species Myotis lucifugus (LeConte 1831). Six subspecies have been recognized (Fenton and Barclay 1980), but overlapping ranges and hybridization have called into question these subspecific desinations (Laussen et al. 2008).

B. Description

The little brown myotis is a small North American bat with variable coloration ranging from pale to dark brown, which is often described as “dark sooty brown through paler golden” dorsally and “pallid, to yellowish or olive brown” ventrally (Fenton and Barclay 1980). Adult body mass ranges between 7 - 9 g (Kalcounis and Brigham 1995; Kunz et al. 1998) and can increase by 30% during pregnancy (Hughes and Rayner 1993; Kurta and Kunz 1987). Length of forearm ranges from ca. 31 - 41 mm and wingspan ca. 250 - 270 mm (Kalcounis and Brigham 1995). The length of the head and body is ca. 54 - 57 mm (Williams and Findley 1979) and length of the tail is ca. 36 - 42 mm (Kalcounis and Brigham 1995). The little brown myotis can be distinguished from similar sympatric species, such as the Indiana myotis (M. sodalis) and northern long-eared myotis (M. septentrionalis), by the length of ears and tragus, pelage length and sheen, lack of a keeled calcar, and ear color (Barbour and Davis 1969). Recordings of echolocation calls and genetic analysis have greatly increased accuracy of species identification (Rodhouse et al. 2008). Although sexes are similar in appearance, adult males are often smaller than adult females (Kalcounis and Brigham 1995).

First year survival of female little brown myotis ranges from 23-46% and is higher for young born earlier in the summer (Frick et al. 2010a). Adult survival rate was 63-90% from 1993-2008 (Frick et al. 2010a). The oldest recorded wild, free-ranging little brown myotis was 31 years when last captured (Fenton and Barclay 1980).

C. Geographic Distribution

As the map below depicts, in the early 1980’s, the little brown myotis was geographically distributed across North America from Alaska to Nova Scotia in the north, and from northern Florida to central Mexico east of the Sierra Madre Occidental in the south (Fenton and Barclay 1980). Distribution is limited by the availability of suitable caves and mines for hibernation, temperatures inside hibernacula, and by the length of the hibernation season (Humphries et al.

2002; Humphries et al. 2006). Although no study has directly connected population density of little brown myotis to cave availability, it is believed that the high density of caves in the Appalachian Mountain range and eastern Midwest (Culver et al. 1999) support much larger populations of this species than in other parts in the species’ range. The largest known colonies of little brown myotis are in the northeastern and mid-western United States, with the northeastern population considered the core range of the species.

–  –  –

D. Habitat

1. Winter Habitat/Hibernacula In the late summer and fall, individual little brown myotis depart from summer roosts and migrate to a variety of transient roosts (Fenton and Barclay 1980) before arriving at winter hibernacula located up to 300 km from summer roosts (Davis and Hitchcock 1965; Fenton 1970;

Griffin 1970; Humphrey and Cope 1976), or perhaps as far as 1,000 km (Wilson and Ruff 1999).

Caves and mines serve as swarming sites during the autumn mating period and as hibernacula during the cold months. Swarming behavior in little brown myotis occurs from August through early October, which also coincides with the pre-hibernation fattening period (Kunz et al. 1998;

McGuire et al. 2009). Hibernacula (or winter roosts) appear to be selected by bats for their high humidity and relatively stable, cool temperatures that are above freezing (Fenton 1970;

Hitchcock 1949; Humphrey and Cope 1976). The duration of hibernation in the little brown myotis depends largely on climate and the length of the hibernal period for a given sector of its range. Although fidelity to hibernacula may differ between males and females (Thomas et al.

1979), little brown myotis often returns annually to swarm, mate, and hibernate at the same site (Davis and Hitchcock 1965; Humphrey and Cope 1976).

2. Spring, Summer, and Fall Habitat

In spring, little brown myotis form maternity colonies of reproductive female bats in barns, attics, tree cavities and other places that remain dark throughout the day (Crampton and Barclay 1998; Hitchcock and Davis 1965). These colonies range in size from tens to hundreds of individuals. Roost fidelity of females to summer roosts tends to be high with adult females typically returning to their natal roosts (Frick et al. 2010a; Reynolds 1998). Warm microclimates in maternity roosts help optimize gestation and postnatal growth of offspring (Baptista et al. 2000; Davis and Hitchcock 1965; Fenton 1970; Humphrey and Cope 1976; Kunz and Anthony 1982). Thus, non-reproductive females and adult males usually inhabit separate

–  –  –

The little brown myotis is opportunistic in selecting its roost sites, “taking shelter in any sites with appropriate microclimates, and quickly locating and exploiting new roosts” (Fenton and Barclay 1980). Flexible behavior may have led to the overall success of this species in exploiting fragmented agricultural landscapes (Henderson et al. 2009) and suburban areas with buildings that are frequently occupied during warm months, yet continued fragmentation of landscapes into smaller patches and reduced availability of buildings for roosting are certain to have adverse affects on little brown myotis populations.

E. Foraging

The little brown myotis feeds on small (3 - 10 mm) aerial insects (Anthony and Kunz 1977). Specifically, the diet of this species is comprised mostly of the insect orders Diptera, Lepidoptera, Coleoptera, Thrichoptera, Ephemeroptera, and Neuroptera with about the same frequency as these insects are available in the foraging area of bats (Anthony and Kunz 1977).

In many areas, this bat feeds over open water and at the margins of bodies of water and forests (Anthony and Kunz 1977; Barclay 1991; Belwood and Fenton 1976; Fenton and Bell 1979;

Saunders and Barclay 1992). However, foraging habitats appear to vary depending on intraspecific competition and flight ability. Juveniles tend to prefer foraging in clearings or open forest roads, whereas adults regularly forage in more cluttered environments (Crampton and Barclay 1998, van Zyll de Jong 1985). Adults also may prefer more open areas, especially when bat population density is high (Adams 1997).

The little brown myotis often engages in two or more feeding bouts per night, occupying remote night roosts to rest and digest between bouts (Anthony and Kunz 1977; Anthony et al.

1981; Kunz 1980). Foraging range for pregnant little brown myotis can exceed 30 hectares, but this range decreases during lactation when adult females return to the day roost to suckle young between evening and morning foraging bouts (Henry et al. 2002). Pregnant and lactating little brown myotis in New Hampshire consume, on average, 2.5 g and 3.7 g of aerial insects during their first nightly feeding bout, while juveniles consume 1.8 g during this same period (Anthony and Kunz 1977). During peak energy demands, lactating females are known to consume the equivalent of their body mass (ca 7 g) each night (Kunz 1980; Kurta et al. 1989).

F. Reproduction

The little brown myotis mates at swarming sites that also serve as hibernacula (Davis 1964; Davis and Hitchcock 1965; Fenton 1969; Hall and Brenner 1968; Kunz et al 1998;

Schowalter 1980; Thomas et al. 1979). At these sites, bats copulate indiscriminately and promiscuously beginning in August, and males sometimes mate with torpid females throughout the hibernation period (Thomas et al. 1979). Some bats that visit a swarming site may relocate to alternative hibernacula prior to entering hibernation (Fenton 1969; Thomas et al. 1979). Thus, mating activity at swarming sites can lead to genetic mixing among roosting or hibernating colonies (Carmody et al. 1974). Females may be reproductively active during their first year of 5 life, but males are not sexually mature until their second fall swarming opportunity (Thomas et al. 1979). Reproductive rates of females are high, averaging 95% from 1993 to 2008 (Frick et al.


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