Keen's long-eared bat (Myotis keenii) COSEWIC assessment and status report: chapter 8
Limiting Factors and Threats
Habitat loss
There are inadequate habitat data to demonstrate that M. keenii is limited to old growth coastal forests but this bat has been primarily captured in these habitats and forages under the canopy of old growth forests. A number of studies have demonstrated that, while some bat species may forage along the edges created by cut blocks (Grindal, 1996), few bats forage in the clear cuts themselves or in the dense second growth forest that follows (Thomas, 1988; Parker et al., 1996; Humes et al., 1999; Ericksen and West, 2003). Tree roosting bats also rely heavily on old growth forests to provide suitable roost trees (Kellner, 1999; Grindal, 1998, 1999). It remains unknown what sort of a barrier an open cut block might create for forest dwelling bats but current logging practices may be seriously fragmenting habitat. Habitat loss is thus a concern as coastal old growth forest continues to be lost to harvesting. On Haida Gwaii, for example, almost 60% of the old growth available to the logging industry has been eliminated (Gowgaia Institute, 2002), and the remaining old growth continues to be logged.
Disturbance
On Vancouver Island, caves associated with karst landscapes are used for swarming and as hibernacula, and M. keenii has been verified at eight different caves. With the hibernation period extending from October to mid-May, and the swarming period from August to September (Mather et al., 2000), these caves are used by M. keenii for nearly 10 months. Hibernating bats are particularly vulnerable to disturbance, and even brief visits by humans without physical disturbance are enough to cause them to arouse (Thomas, 1995). Arousals are energetically costly -- each winter arousal burns the same amount of fat as would be used in 68 days of torpor (Thomas et al., 1990). Swarming bats could also be affected by disturbance near the cave entrance.
Recreational caving and forest harvesting activities are potential disturbances at these caves. Cavers using these caves during the hibernation period will disturb hibernating bats, and as caving increases in popularity, this disturbance could become a significant factor in the over winter survival of bats. Although forest harvesting activities around cave entrances do not appear to alter cave microclimate (Davis et al., 2000a), logging debris may accumulate in the entrance and block access. The effects of blasting and other activities associated with logging road construction are unknown, but seismic effects and other noise could disturb hibernating bats.
The only known maternity colony at Gandl K’in Gwaayaay is located within 50 m, and some case < 10 m, of bathing pools that are frequently used by visitors. Roost sites have been identified, however, and measures have been put in place to minimize disturbance from visitor activities.
Predation
M. keenii’s behaviour of flying and roosting close to the ground makes it vulnerable to predation by cats. It is difficult to quantify this predation but at least three individuals have been killed in this way in Sandspit alone (Burles, unpublished data), and a number of museum specimens from other parts of its range are also from cat kills.
As a bat that frequently roosts in cliffs or caves, M. keenii may be vulnerable to predators such as rodents or raccoons that could enter or reach into their roosts. The presence of mice (Peromyscus spp.), a known predator of hibernating bats, in the Weymer caves is noteworthy but their impact on hibernating bats in these caves has not been studied. Keen’s Mouse is present on Gandl K’in Gwaayaay in close proximity to the roosts but their impact on the maternity colony is also unknown.
On Haida Gwaii, where the islands’ native fauna is depauperate, introduced mammals have become serious predators. Raccoon predation on seabirds has been documented (Hartman, 1993; Golumbia, 2000), and like cats, may be capable of capturing M. keenii as they forage. Rats (Rattus rattus, Rattus norvegicus) and red squirrels (Tamiasciurus hudsonicus) have also been documented as predators of seabirds and songbirds (Harfenist, 1994; Martin et al., 1994; Martin et al., 2001), and if either were ever introduced to Gandl K’in Gwaayaay, could have a devastating impact on the colony there.
In assessing the status of M. keenii, the following unanswered questions must be kept in mind:
- What is its taxonomic relationship with M. evotis?
- Is it truly rare or is it simply difficult to capture in mist nets or harp traps?
- Where does the majority of the population hibernate?
- What habitat or habitats are vital for foraging and summer roosting?
- Is it strongly dependent on old growth forests?
- What are the immediate threats to hibernacula and foraging habitats?
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