Keen's long-eared bat (Myotis keenii) COSEWIC assessment and status report: chapter 5

Habitat

Habitat requirements

Summer roosts

There are few records of M. keenii roosting behaviour (Table 1), and only two maternity colonies are known. At Gandl K’in GwaayaayFootnoteb, both M. keenii and the little brown Myotis (M. lucifugus) roost in close association with a hot springs. Three bathing pools have been developed around these springs and they have become a major tourist attraction. Most bats roosted about 50 m away from bathing pools under large boulders, in crevices, and in a small cave that were heated by hot water (Firman et al., 1993; Burles, 2000). Most M. keenii roosted underneath a very large boulder about 1 m above the extreme high tide line, and in a small cave that was located about 10 m away and about 3 m above extreme high tide. Some M. keenii also used a heated 3 – 5 cm wide crevice located in a 1 m diameter gap in the salal (Gaultheria shallon) located about 1 m above the main bathing pool. Use of this roost was sporadic and may have been influenced by the level of use of the bathing pool (Burles, 2001). Two radio-tagged individuals were tracked to crevices in shoreline cliffs that were only 1 cm wide, and one individual also roosted in a crevice in a 2 m diameter boulder in the thermal meadow about 30 m from the shoreline. Water temperatures of up to 50 °C and air temperatures of up 34 °C were recorded in some passages near roosts. Reproductive females used these nursery roosts from late May until about the middle of August, when they presumably left for hibernation sites. Some juveniles continued to make use of these roosts until the middle of September. The two species using the Gandl K’in Gwaayaay roosts do not appear to roost together as M. keenii is capable of using much narrower crevices than M. lucifugus. In all instances, M. keenii appeared to use small crevices or hollows suggesting that they may roost solitarily or in very small numbers, similar to M. evotis in Alberta (Chruszcz and Barclay, 2002).

Another maternity colony was found at Knoll Hill near Tahsis, Vancouver Island. A nursing M. keenii (identified from mtDNA taken from wing punches) captured at a cave entrance was subsequently radio tracked to a low elevation roost in a lodgepole pine (Pinus contorta) snag but the signal was lost shortly afterward (Mather et al., 2000). It was not possible to determine whether it had initially been roosting inside the cave, in a cliff crevice or in a nearby snag prior to capture. In other studies on Vancouver Island, Grindal (1999) and Kellner (1999) both radio-tracked reproductive female M. keenii/ M. evotis to tree roosts (N=3) located in old-growth forest.

Table 1. Known roosting data for Keen’s long-eared bat (Myotis keenii).
Type of Structure Roost type Location Remarks SourceFootnotea
Natural Small cave, rocks hydrothermally heated Haida Gwaii, Gandl K’in Gwaayaay, BC Maternity colony; known for 40 years Firman et al. (1993), Burles (2001)
Natural Cave Labyrinth Cave, Vancouver Island, BC Hibernaculum. 2 M. keenii skeletonsFootnoteb found in cave, long-eared myotis observed in cave and caught swarming at entrance Nagorsen (1995), Mather et al. (2000)
RBCM 19500 (identified by D. Nagorsen), 19507 (identified by S. van Zyll de Jong)
Natural Cave Marmot Mausoleum Cave, Vancouver Island, BC Hibernaculum? Skull (missing teeth) found in cave Probably M. keenii; identified by D. Nagorsen; Mather et al. (2000)
Natural Tree on cliff Knoll Hill, Vancouver Island, BC Maternity colony? Nursing female captured in small cave 9 August, then tracked to tree roost Mather et al. (2000). Radio-tracked; identification verified from mtDNA taken from wing punch sample
Natural Rock crevice, tree roost Kamikaze Cave, Vancouver Island, BC Male, originally caught at cave entrance 1 Sept, tracked to roost in crevice, then moved to tree Mather et al. (2000). Radio-tracked; identification verified from mtDNA taken from wing punch sample
Manmade Attic of cannery Chicagof Island, Hoonah, AK Adult male, 11 July Parker and Cook (1996); UAM 29831
Manmade House Lake Cushman, WA Adult female, 24 July Dice (1932); UMMZ 52920
Manmade House Kingcome Inlet, BC Adult female, 11 September taken in Myotis yumanensis nursery colony CMN 14650; field notes
Manmade House Telegraph Creek, BC Adult female, 7 Sept., caught in Hudson Bay store? Heller (1914), USNM 209856
Manmade House Campbell River, BC In valance of house, July, sex? RBCM 13356
Manmade Bridge Olympic National Forest, Sol Duc River, WA Night roost, under bridge, 2 females
15 July
Vouchers taken by Tanya Dewey, identification verified from mtDNA
Manmade Bridge Olympic National Forest, Dosewallips River, WA Night roost, under bridge, 1 female
20 July
Voucher taken by Tanya Dewey, identification verified from mtDNA

Non-reproductive bats appear to roost separately from maternity colonies, at least early in the season, but may join the colony as summer progresses. At Gandl K’in Gwaayaay, only reproductive females were captured around the nursery roosts during May and June. The first males were captured in early July, and by August 40% of adults captured were either males or non-reproductive females (Burles, 2001). On Vancouver Island, a male (identified as M. keenii from mtDNA taken from a wing punch) captured near Tahsis on 1 September was relocated the following two days in a crevice in a SW facing limestone outcrop at about 750 ASL (Mather et al., 2000). On the 3rd day it was located in a 40 m high western hemlock (Tsuga heterophylla) where it roosted about 30 m up in the canopy. These researchers also tracked a non-reproductive female M. keenii/M. evotis to 3 different crevice roosts in SW facing limestone outcrops (50 – 270 m ASL). Each evening it was seen to emerge along with 3 or 4 other bats. Kellner (1999) also radio-tracked two male M. keenii/M. evotis to 3 different crevices in a granite quarry, and Kellner and Rasheed (2002) radio-tracked 3 non-reproductive female M. keenii/M. evotis to south facing cliffs (N=3) and a snag (N=1) located in old-growth forest.

Data from museum specimens and Parker and Cook (1996) demonstrate that M. keenii also roosts in buildings. There are at least five occurrences of this species being found in buildings (Table 1); all appeared to be solitary individuals. M. keenii has also been found to roost at night under bridges in Washington (T. Dewey, unpublished data).

Foraging habitat

Little information on habitat use by M. keenii is available because of difficulties studying such a small and secretive animal. Efforts to place radio tags or light tags on individuals have met with only limited success (MacKay et al., 2000; Mather et al., 2000; Burles, 2001). Most information on habitat use then, must be derived from ecomorphological characteristics, capture records and studies on other similar species.

Morphological characteristics, such as relatively short, broad wings and long ears, suggest that long-eared bats like M. keenii are slow, maneuverable fliers (Fenton and Bogdanowicz, 2002; Burles, 2001). They also have a high frequency, low intensity echolocation call, which should enable them to fly in relatively cluttered environments (Burles, 2001; Fenton, 1972). Their relatively long ears and thus sensitive hearing allow them to detect sounds generated by prey and thereby glean them from vegetation, as was predicted by Fenton (1990). Together, these characteristics allow M. keenii to forage within spatially complex old growth forests where most other bats find it difficult to, and to continue to forage even when adverse weather conditions, such as rain or cool temperatures, prevent insects from flying (Barclay, 1991). The ability to glean prey also enables this species to prey on spiders, one of the more common invertebrates in coastal rainforests.

Historical records support the conclusion drawn from morphological studies in that the distribution of M. keenii appears to be limited primarily to temperate coastal rainforests (Nagorsen and Brigham, 1993). Most recent observations also support this generalization, although a few occurrences from urban areas have been recorded. At Gandl K’in Gwaayaay, M. keenii were regularly observed to emerge from their shoreline roosts about 30 minutes after sunset, and to fly into adjacent old growth western hemlock – Sitka spruce (Picea sitchensis) forest (Burles, 2001). M. keenii were captured 100 – 200 m inland from these roosts at less than 3 m above ground, indicating that once they entered the forest at least some individuals foraged near ground level. Use of old growth forest may be from necessity, however, as there is virtually no open habitat on Gandl K’in Gwaayaay, with the exception of shorelines and two small thermal meadows.

Near Hazelton, where M. keenii, M. evotis, and M. septentrionalis were all captured at a single location, radio-tagged bats continued to forage in the area of capture over the next 11 – 14 days (MacKay et al., 2000). Although all were captured near a pond, they subsequently foraged primarily within the adjacent western red cedar (Thuja plicata) – western hemlock forest, rather than over open water. In southeast Alaska, one M. keenii was captured within 1 m of a cliff in a riparian forest dominated by large western hemlock and Sitka spruce (Parker and Cook, 1996). On Vancouver Island, M. keenii/M. evotis were captured in riparian or estuarine habitats associated with mature coastal western hemlock forests (Davis et al., 2000b; van den Driessche et al., 1999; van den Driessche et al., 2000), and radio tracking indicated that they foraged in estuaries (Mather et al., 2000). Both Grindal (1999) and Kellner (1999) found that riparian habitats were the most important foraging habitats for bats, including long-eared Myotis, on Vancouver Island.

Studies of other long-eared species generally support the inferences made above. In western Oregon, female M. evotis preferentially foraged in terrestrial habitats less than 100 m away from water, although they seldom foraged directly over the water (Waldien and Hayes, 2001). They often exhibited strong fidelity to a relatively small foraging area (mean size 38 ha), and these activity areas occurred in all ages of forest stands. Radio tagged bats emerged an average of 20 minutes after sunset, foraged for an average of 4.2 activity periods and then returned to their day roosts about 2 hrs before sunrise.

Hibernacula

Recent research by Davis et al. (2000b) and Mather et al. (2000) indicates that M. keenii hibernates in montane caves associated with karst formations on northern Vancouver Island. Bats verified as M. keenii from skulls or mtDNA analysis of wing tissue, have been found in association with eight caves from three separate areas: Weymer Creek near Tahsis, White Ridge near Gold River, and the Hankin Range east of Nimpkish Lake. M. keenii were captured in late summer at the entrances of seven caves. These captures presumably represented 'swarming', a behaviour associated with hibernation where bats make nocturnal flights through potential hibernacula (Fenton 1969; Schowalter, 1980). Additional evidence for the use of caves as hibernacula are observations of hibernating long-eared Myotis (M. keenii/M. evotis) inside two caves at Weymer Creek, and the recovery of skulls verified as M. keenii from deep inside two caves in this area (Table 1). Unidentified long-eared Myotis (M. keenii/M. evotis) were also captured at the entrances of three other caves in the Weymer area, providing additional evidence that caves are important for long-eared Myotis.

According to Mather et al. (2000), swarming began at the Vancouver Island caves in early August and extended until early September. The most common species caught while swarming were M. lucifugusand the long-legged Myotis (Myotis volans), with long-eared Myotis (M. keenii /M. evotis) representing about 15% of the bats captured at cave entrances. Fenton (1969) described two swarming phases: an early phase with nocturnal flights but no breeding, and a later phase that includes copulation and the build up of hibernating populations. Mather et al. (2000) did not observe any sexual activity during their study and it is unknown if mating occurs at these caves. The proportion of the bats captured swarming at the Vancouver Island caves that actually hibernate in these caves is unknown. These hibernacula supported small numbers of bats that hibernated singly or in small clusters.

Although the caves studied by Mather et al. (2000) ranged in elevation from 4 m to 945 m ASL (maximum elevation in this area =1126 m ASL), only the higher elevation ones (550 m – 945 m) were used as hibernacula, and the largest aggregations were in caves above 800 m. Bats hibernated deep in the caves (100 m inside) where the mean winter temperature remained stable between 2.4° to 4.0°C throughout the winter. The caves located at lower elevations (< 600 m) they found, were warmer and had more variable temperature profiles, conditions that result in higher body temperature (and thus increased metabolism), and more frequent arousals (Thomas et al., 1990). Hibernating in these caves would probably require greater energy reserves than most bats accumulate. High elevation caves with stable cold winter temperature regimes thus may be critical for hibernation by M. keenii.

No hibernacula of long-eared Myotis are known from the mainland coast or the British Columbian interior (Nagorsen et al., 1993). In September 2001 an attempt was made to locate hibernation sites on Haida Gwaii (Fenton et al., 2002). Radio tagged M. lucifugus were all found to be still using tree roosts, which led these authors to speculate that because of the moderate climate and stabilizing influence of the nearby ocean, it is possible that bats on Haida Gwaii could hibernate in tree snags along the shoreline. Subsequent research has shown that bats do occasionally become active throughout the winter (Burles, unpublished data), which lends support to the hypothesis that some bats probably hibernate in trees. Alternatively, M. keenii may use montane caves for hibernation on Haida Gwaii similar to Vancouver Island. Montane caves have been recently discovered in karst formations and there are unconfirmed reports from cavers of bat skulls in caves.

Trends

Although it is not known how dependent this species is on old-growth forests, it is certain that M. keenii forages within these stands. There is also evidence that few bats use central portions of clearcuts (Grindal, 1996), or dense second growth forests (Parker et al., 1996), so the cutting of old growth forests does represent habitat loss for this species.

On Haida Gwaii almost 60% of the old growth available to the logging industry has been logged, most in the last 30 years, and old growth continues to be logged (Gowgaia Institute, 2002). Efforts are currently underway to modify second growth forests to make them more suitable for wildlife, including bats (T. Glasman, personal communication), although the extent of these modifications is limited.

Protection/ownership

Both of the known maternity colonies occur in protected areas. The maternity colony at Gandl K’in Gwaayaay is within Gwaii Haanas National Park Reserve and Haida Heritage Site. The Knoll Hill site, adjacent to Weymer Cave Provincial Park is designated as a Wildlife Habitat Area. Several hibernacula on Vancouver Island occur within Weymer Cave and White Ridge Provincial Parks. Most of M. keenii’s range, however, is on private, Aboriginal, or Crown lands that are subject to forest harvesting. With so little known of its’ distribution, particularly in the central and north coast regions, we cannot estimate the proportion of the Canadian range in these different land tenures. It is noteworthy that the British Columbia Provincial Forest and Range Practices Code only regulates forest harvesting practices on provincial Crown land. 

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