Aspects of the Winter Ecology of Bats on Haida Gwaii, British Columbia Author(s): Douglas W BurlesM Brock FentonRobert MR BarclayR Mark BrighamDiane Volkers Source: Northwestern Naturalist, 95(3):289-299. 2014. Published By: Society for Northwestern Vertebrate Biology DOI: http://dx.doi.org/10.1898/12-32.1 URL: http://www.bioone.org/doi/full/10.1898/12-32.1

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BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research. NORTHWESTERN NATURALIST 95:289–299 WINTER 2014

ASPECTS OF THE WINTER ECOLOGY OF BATS ON HAIDA GWAII, BRITISH COLUMBIA

DOUGLAS WBURLES Gwaii Haanas National Park Reserve and Haida Heritage Site, Kamloops, BC V2B 8A8 Canada; [email protected]

MBROCK FENTON Department of Biology, University of Western Ontario, London, ON N6A 5B7 Canada

ROBERT MR BARCLAY Department of Biological Sciences, University of Calgary, Calgary, AB T2N 1N4 Canada

RMARK BRIGHAM Department of Biology, University of Regina, Regina, SK S4S 0A2 Canada

DIANE VOLKERS Banff National Park, Banff, AB T1L 1K2 Canada

ABSTRACT—Bats of the temperate region of North America avoid winter by some combination of migration and hibernation at a location that provides the right conditions for minimizing energy expenditure over winter. Such optimal conditions are commonly found underground, and most of the best known hibernacula occur in caves or mines. Where winters are milder, some bat species hibernate in hollows in trees. Haida Gwaii, British Columbia, has the dual distinction of being relatively far north in terms of bat distribution, but with a relatively moderate oceanic climate. We hypothesized that because of the moderate winter temperatures, hibernating in trees could be an option for bats on Haida Gwaii. We used data loggers to monitor temperatures inside potential roost trees during 9 winters between 2002–2003 and 2012–2013. We found that mean winter temperature inside the trees ranged from 2.3–6.56C, and in most years temperatures either did not drop below freezing or else did so only for short periods of time. We calculated that a 6 g bat would have required between 2.49–2.92 g of fat to hibernate in the tree roosts that we monitored, which is well within the limits that Little Brown Myotis (Myotis lucifugus) are known to accumulate in autumn. Our acoustic data demonstrated that California Myotis (Myotis californicus) were periodically active during all winter months except December, which we view as evidence that this bat hibernates locally either in trees or buildings. The absence of Little Brown Myotis, Keen’s Myotis (Myotis keenii) and Silver-haired Bat (Lasionycteris noctivagans) observations during winter suggests that they may either use more common hibernacula, such as caves, or migrate off the islands.

Key words: British Columbia, California Myotis, Haida Gwaii, hibernation, Keen’s Myotis, Little Brown Myotis, Silver-haired Bat, winter bat activity

For insectivorous bats in temperate regions, for minimizing over-winter energy expenditure winter is a time of food shortage, reflecting the and water loss. These conditions vary some- general lack of activity and availability of insect what depending on species, but generally and other arthropod prey. Bats of the temperate include cool, stable temperatures with high zone in much of North America avoid winter by relative humidity (Altringham 1996). For small some combination of migration and hibernation bats, such as Little Brown Myotis (Myotis (Fenton 2001). In most cases, the locations that lucifugus) hibernating in Kentucky and New bats choose as hibernacula provide conditions Jersey, the optimal temperature of hibernacula

289 290 NORTHWESTERN NATURALIST 95(3) is approximately 26C (Hock 1951; McManus Haida Gwaii (formerly the Queen Charlotte 1974), and any variation from this temperature Islands), British Columbia, Canada, at 52–546N, results in an increase in metabolic rate. Stable has the dual distinction of being relatively far temperatures also have an influence on hiber- north in terms of bat distribution, but with a nation success as frequent temperature fluctu- relatively moderate oceanic climate. Sandspit, ations cause more frequent arousals resulting in for instance, which is 6 m ASL and ,1 km from greater energy expenditures (Ransome 1971; the ocean, experiences an average of 330 frost- Twente and others 1985). High humidity at free d/y (Canadian Climate Normals 1993). hibernation sites is also an important factor as Haida Gwaii is separated from southeast Alaska water loss due to metabolism occurs even in to the north by the 60 km-wide Dixon Entrance deep torpor, and the rate of water loss is and from mainland British Columbia to the east thought to influence the duration of bouts of by the 60 to 100-km-wide Hecate Strait. The torpor (Thomas and Geiser 1997). archipelago may be sufficiently isolated that For some populations of bats, optimal condi- few, if any, bats migrate from the islands to tions for hibernation are found underground, overwinter elsewhere. and most of the documented hibernacula are in Four species of bats occur on Haida Gwaii. caves or mines. For example, in much of their Keen’s Myotis (Myotis keenii) is relatively rare, geographic range, Little Brown Myotis usually known from only a few locations (COSEWIC hibernate underground in caves or mines 2004). The only known roosts are in heated rock (Fenton and Barclay 1980). In more southerly crevices associated with a hot spring (Burles regions of North America and Europe, some and others 2008), although they likely also species of bats hibernate in hollows in trees occasionally roost in trees and in buildings, as (Altringham 1996). In eastern Canada and the elsewhere (Parker and Cook 1996; Mackay and United States, hibernation in underground others 2000; Davis and others 2000; Boland and locations exposes bats to white-nose syndrome, others 2009). Little Brown Myotis and California which has decimated some bat populations Myotis (M. californicus) are both relatively since its arrival in 2006 (Warneke and others common. On Haida Gwaii, Little Brown Myotis 2012). Less is known about where bats hibernate have also been found roosting in heated rock in western North America, and no large crevices, as wells as in trees (Burles 2001). Little hibernacula are known west of the Rocky is known of roosting habits of California Myotis Mountains. In southeast Alaska, over 400 caves on Haida Gwaii, but elsewhere they roost in have been investigated with only small num- hollows, cracks, and crevices in trees (Brigham bers of bats being recorded in a few caves and others 1997). Silver-haired Bats (Lasionyc- (Lewis 1997; K Blejwas, Alaska Department of teris noctivagans) are relatively uncommon on Fish and Game, pers. comm.) In British Colum- Haida Gwaii. They generally roost in hollows in bia, bats have been reported hibernating in .60 trees or under pieces of loose bark (Parsons and caves or mines, but invariably only small others 1986; Barclay and others 1988; Betts numbers have been observed (DW Nagorsen, 1998). Of the 4 species, the Silver-haired Bat is Mammalia Biological Consulting, pers. comm.). the only species known to be capable of flying On Vancouver Island, for instance, where caves across large bodies of water (McGuire and have been extensively surveyed, Davis and others 2012) and thus could potentially migrate others (2000) found evidence of bat activity in to the mainland. 15 of 31 caves investigated, but observed only We studied aspects of the winter ecology of small numbers of myotis (up to 45 individuals) bats on Haida Gwaii. Information on winter in 5 caves. The only exception appears to be a activity and hibernacula are lacking for much of mine in the east Kootenays that may support in coastal British Columbia and adjacent Alaska. excess of 100 hibernating bats (CL Lausen, We hypothesized that because of the moderate Wildlife Conservation Society, pers. comm.). winter temperatures experienced on Haida Similarly, in the northwestern United States, Gwaii, bats could potentially hibernate in trees. only small numbers of bats have been found in Based on this hypothesis, we made the follow- a few caves or mines (Perkins and others 1990; ing predictions: (1) winter temperatures in Kuenzi and others 1999). hollows and spaces under bark of trees will be WINTER 2014 BURLES AND OTHERS:WINTER BAT ECOLOGY ON HAIDA GWAII 291 mainly .06C; and (2) tree hollows will be more Mean winter temperature, standard deviation, useful as hibernacula for bats than spaces under and minimum and maximum temperatures bark. We also acoustically monitored for bats were determined for each data set. throughout the winter to determine species presence and activity. Winter Energetic Modeling To further explore the feasibility of bats METHODS hibernating in hollows or crevices in trees on Potential Hibernation Trees Haida Gwaii, we used the formulas of Hum- We used Ibutton Thermocron data loggers phries and others (2006) to determine how (Dallas Semiconductor Corp., Dallas, Texas) to much fat would be required for a Little Brown monitor temperatures in crevices or hollows Myotis to hibernate in trees, with one exception. Rather than using the metabolic rate for torpor and under the bark of potential bat roost trees to 6 determine if it was feasible for bats to hibernate (TMR) of a bat hibernating at 2 C (the lower in trees on Haida Gwaii. Although the data ambient set point temperature, Ts, or tempera- loggers are rated by the manufacturer as being ture at which TMR is least) of 0.03 ml O2/g/h as accurate within ± 16C, we first confirmed this determined by Hock (1951), we chose to use the by placing 1 data logger next to the weather TMR of 0.02 ml O2/g/hr as calculated by instruments at the Sandspit airport weather Thomas and others (1990a). We chose this value station (YZP, 53.2506N, 131.8126W) and set it to because Jonasson and Willis (2012) found that it record hourly for a week. We then compared better predicted actual energy expenditures of the temperatures it recorded with those record- hibernating bats in Manitoba than did Hock’s ed by the weather station and calculated the estimate of TMR. Thus, when Ta exceeded Ts, average difference in the temperature. This the energetic cost of torpor (Etor) was calculated (Ta-Ts)/10 average difference was later used as a correction as Etor 5 TMR*Q10. factor for all temperatures recorded by this The value for Q10 (the change in torpor device during experiments. All other data metabolism resulting from a change in ambient loggers used in our study were calibrated with temperature, Ta) was calculated as 1.6 + 0.26 Ta the original data logger to minimize differences 2 0.006 Ta. When Ta , Ts,Etor was calculated as among devices, as well as between the devices Etor 5 TMR + (Ts 2 Ta)Ct. In the latter formula, and YZP temperatures. torpor conductance (Ct, a measure of the ease During winters 2002–2003 and 2003–2004, we with which heat flows between the animal and monitored ambient temperatures in 2 known the surrounding air) was set at 0.055 ml O2/g/ 6 and 1 potential roost tree located on Huxley C. The above formulae allowed us to calculate Island (52.4416N, 131.3636W). Because it was the number of ml of O2 a bat would consume logistically difficult to get to Huxley Island, in during a specific time period at a specific 2004 we shifted our observations to Skidegate temperature. Given that 1 ml of O2 is equivalent Inlet (53.2266N, 131.9456W), choosing another 3 to the consumption of 20.1 Joules (from fat), and potential roost trees near the shoreline where that fat contains 39.3 kJ/g, we could then we thought that proximity to the ocean would calculate the amount of fat consumed under moderate ambient temperatures. Beginning in those conditions. 2006, we focused all our efforts on 1 tree with a Using the temperatures recorded in our deep cavity. In 2005–2006, 2010–2011, 2011– experimental trees we calculated the amount 2012, and 2012–2013 we placed data loggers of fat required for a 6 g bat, the approximate both inside and under the outer bark of 1 of the mass of Little Brown Myotis in summer on study trees (SI #1) to assess whether a bat could Haida Gwaii (Burles and others 2009), to hibernate under the bark. In each case, the data hibernate in each of our study trees from 1 loggers were programmed to record tempera- November to 30 April the following spring. To tures every 2 or 3 h between 1 November and 30 determine this we calculated Etor for each 2–3 h April the following year. We also obtained daily interval between 1 November and 30 April each temperature records for winter months from year, and then summed all calculations to 2000–2001 to 2012–2013 from YZP as a general estimate overall winter costs of torpor. We measure of ambient temperature for the area. also used mean winter temperatures from the 292 NORTHWESTERN NATURALIST 95(3)

Sandspit airport to calculate fat requirements for (96.4 ± 4.0 Khz, a 5 0.05, n 5 48), which results hibernation for winters 2002–2003 to 2012–2013 in a call with a much steeper slope (23.3 vs. to see if this more generalized estimate of fat 11.3 Khz/msec). Silver-haired Bats have rela- requirements was comparable to our calculations. tively long-duration calls of 10.4 ± 1.1 msec that As our model does not take into account the sweep from about 36.4 ± 2.7 Khz down to 25.7 energetic costs of arousals, we used Thomas and ± 0.4 Khz (a 5 0.05, n 5 10). others’ (1990b) estimate of 108 mg of fat consumed during a 3-h arousal and an estimate Radio-telemetry of the average torpor bout lasting about 13 d We used radio-telemetry to locate the roosts of (Twente and others 1985; Jonasson and Willis Little Brown Myotis at 2 locations in Gwaii Haanas 2012), or 14 arousals per winter, to determine National Park Reserve and Haida Heritage Site – the energetic costs of arousals as 1.51 g per Gandll K’in Gwaayaay (52.5766N, 131.4436W) and winter. This figure was added to each estimate Huxley Island. Between 10 to 24 September 2001, of the winter cost of torpor to determine the we captured bats using 6-, 9-, or 12-m long mist overall amount of fat a bat would require to nets as they emerged from roosts near the hot survive each winter. springs on Gandll K’in Gwaayaay or flew along the shore on Huxley Island. Our assumption was Winter Acoustic Surveys that by September bats would be congregating We passively monitored bat activity in a near where they were going to hibernate and we residential area of Sandspit during winter might be able to track them to their hibernacula. months on an opportunistic basis (when tem- We set a harp trap (Tuttle 1974) in an effort to catch perature was .06C, and there was little wind or bats along flyways or at the entrance of a mine adit precipitation) using a bat detector. In 2000–2009, which might have served as a night roost. We also we used a broad band Anabat II detector and recorded the echolocation calls of flying bats using delay switch with a clock (Titley Electronics, the high-frequency output of a Pettersson D980 Ballina, Australia) connected to a cassette tape (Pettersson Electronik AB, Uppsala, Sweden) recorder (CTR-96; Radio Shack, Fort Worth, TX). detector through an Ines DAQ i508 high-speed In 2011 and 2013, a Song Meter SM2BAT auto card to a PC running BatSound Pro. recording system (Wildlife Acoustics, Concord, Radio tags weighing 0.45 g (LB-2; Holohil MA) was used. All recordings were tentatively Systems Ltd., Carp, ON) were glued to the identified to species on the basis of echolocation backs of selected bats using surgical cement call structure. Call parameters (primarily call (Skin Bond; Smith and Nephew Inc., Missis- duration, minimum and maximum frequencies, sauga, ON) after the fur had been trimmed. Bats and call slope) were measured using Anabat5 were chosen to carry a radio tag on the basis of (Titley Electronics, Ballina, Australia) and Bat- non-reproductive status and their size (mass Sound Pro (Petterson Electronik, Uppsala, Swe- .5 g and relatively large wings). Gluing on den), and then compared with those obtained transmitters ensured that they would be shed as from field recordings of known bats (D Burles, the hair grew back. The bats’ activities were unpubl. data), or by making visual comparisons then monitored using a radio receiver (Sure- using Sonobat (Arcata, California). Specifically, track STR 1000; Lotek Engineering Inc., New- California Myotis have short-duration calls of market, Ontario; or a TRX 2000S: Wildlife 2.8 ± 0.2 msec that sweep from 92.3 ± 4.0 Khz Materials Inc., Murpheysboro, IL) with a two- down to a minimum frequency $44 ± 1.2 Khz element directional antenna. Radio-tagged bats (a 5 0.05, n 5 30), while Little Brown Myotis were generally followed for at $1 hour imme- have relatively short-duration calls (3.6 ± diately after release to ensure that the bat 0.2 msec, a 5 0.05, n 5 63) that sweep from remained active. On the following days, the about 76.1 ± 2.8 Khz (a 5 0.05, n 5 63) down to area was surveyed by boat and on foot to locate a minimum frequency of 36.8 ± 0.6 Khz (a 5 where the bat was roosting. Whenever possible, 0.05, n 5 63). Keen’s Myotis calls are similar to the exact tree or rock crevice roost was those of Little Brown Myotis except that they pinpointed. Once a roost was identified, it was are of shorter duration (2.8 ± 0.2 msec, a 5 0.05, monitored the following evening for time of n 5 48) and have a higher maximum frequency emergence and number of bats emerging. WINTER 2014 BURLES AND OTHERS:WINTER BAT ECOLOGY ON HAIDA GWAII 293

TABLE 1. Summary of locations and roost types on Haida Gwaii, British Columbia, in which winter temperatures were monitored to determine the feasibility of bats hibernating at each location. Latitude/ Distance from Elevation Site Longitude Tree type Roost type ocean (m) (m ASL) HU-cave 52.4446 Cave Cave - 50 m in 500 120 –131.3706 from entrance where bat guano found HU #1 52.4386 60 cm dbh Sitka Spruce 25 cm inside 15 10 –131.3626 snag with no bark crevice 3 m above ground HU #2 52.4396 1.5 m dbh Western 75 cm inside 100 50 –131.3636 Redcedar hollow 3 m above ground HU #3 52.4386 1.5 m dbh Western 20 cm inside 300 80 –131.3686 Redcedar hollow 1.5 m above ground SI #1-inside 53.2266 2 m dbh Western 75 cm inside 55 –131.9376 Redcedar hollow 1.5 m above ground SI #1-bark 53.2266 2 m dbh Western Under loose bark 55 –131.9376 Redcedar 1.5 m above ground SI #2 53.2066 2 m dbh Sitka Spruce 20 cm inside 1200 30 –131.9736 snag in advanced hollow 1 m decay above ground SI #3 53.2456 50 cm dbh western 25 cm inside 400 10 –131.8216 hemlock snag woodpecker cavity 5 m above ground

RESULTS temperatures averaged 7.56C and varied be- tween 6.5 to 8.06C. Temperatures under the Conditions of Potential Hibernation Sites outer bark of SI #1 were considerably lower than Between 2002–2003 and 2012–2013, we ob- those inside the tree, with greater extremes and tained 18 temperature data sets during 9 variability (Table 2). The wood of the tree thus winters from 2 used and 4 potential bat roost appeared to have a buffering effect on temper- trees at 2 different locations on Haida Gwaii, atures inside the tree. Temperatures inside the and 1 cave known to have been used by bats study tree were, in turn, considerably cooler in (Table 1). One data set (SI #3) was excluded both years than temperatures recorded at the from our analyses because at some point during airport. the winter the data logger was ejected out of the cavity onto the ground. Winter Energetics Modeling Temperatures inside all the trees we moni- tored remained well above freezing for most of From the temperatures we recorded, we the time in all winters (Table 2). In 5 data sets calculated that a 6-g Little Brown Myotis temperatures did not drop below 06C (Table 2), hibernating in our study trees would require while in a further 8 sets temperatures dipped 2.49 to 2.92 g (n 5 12) of fat to survive the winter below freezing for only short periods of time (1– (Fig. 1). Our 3 estimates for a bat hibernating 9 d). Temperature data from YZP (Table 3) under the bark of SI #1 varied between 2.58 and revealed that the winters during which we 2.89 g (n 5 4). Our highest estimate of fat (2.93 g) monitored conditions were generally typical of required was for a bat hibernating inside the conditions experienced since 2000, with the cave on Huxley Island, which was almost exception of winter 2002–2003, which was identical to our estimate for nearby HU #1 considerably warmer. In the 1 winter that we (2.92 g). Based on the mean winter temperatures had a data logger inside the Huxley cave, for YZP since 2000 we estimated that the 294 NORTHWESTERN NATURALIST 95(3)

TABLE 2. Summary of temperatures recorded at potential bat hibernation sites located on Huxley Island and in Skidegate Inlet, Haida Gwaii, British Columbia, between 1 November and 30 April, during 9 winters, 2002– 2013. Recording intervals were every 2 h in 2002–2003, 2004–2005, and 2005–2006; every 2.5 h in 2003–2004; and every 3 h thereafter (n $ 1212 in all datasets.). *data missing for short time periods; +data logger fell out of cavity part way through the winter. Study location Period monitored Mean 6C Standard deviation Max 6C Min 6C HU #1 2002–2003* 6.5 2.7 11.7 25.8 2003–2004 5.1 2.1 9.7 20.3 HU #2 2003–2004 4.9 2.1 10.0 22.5 HU #3 2003–2004 5.2 1.6 8.5 0.0 HU-cave 2002–2003* 7.5 0.4 8.0 6.5 SI #1-inside 2004–2005* 4.6 1.8 7.2 0.2 2005–2006 4.3 1.7 8.5 0.5 2006–2007 3.7 1.6 8.0 22.0 2007–2008* 3.1 1.8 8.0 20.5 2010–2011 3.5 1.8 8.6 20.7 2011–2012 2.6 1.9 6.8 25.8 2012–2013 3.9 1.1 6.3 1.3 SI #1-bark 2005–2006* 4.1 2.5 11.5 23.0 2010–2011 2.7 2.8 12.1 24.6 2011–2012 2.3 2.7 9.7 210.3 2012–2013 3.6 2.0 9.5 21.3 SI #2 2005–2006 3.7 1.4 8.2 1.2 SI #3 2005–2006+ 4.5 2.6 11.0 22.0 amount of fat required for a bat to overwinter in recorded. California Myotis were by far the Sandspit would have been between 2.50 to 2.75 g most common and were active throughout (n 5 13). winter. The only collection of a bat in winter at Sandspit was a California Myotis freshly Winter Activity Monitoring killed by a cat on 26 February 2005 (D Burles, We acoustically monitored bat activity near unpubl. data). Little Brown Myotis were detect- Sandspit on 157 nights for a total of 674.1 h of ed as late as 25 October and as early as 17 April recording (Table 4), during the winters of 2000– but were not recorded in between. Similarly, 2001 and 2012–2013. Bat activity was recorded Silver-haired Bats, which were regular visitors on 66 occasions during all winter months except at this site in August and September, were December. Ambient temperature ranged be- not detected between late September and late tween 5 to 126C on nights that bat activity was April. Keen’s Myotis, which were occasionally

TABLE 3. Summary of winter temperatures (1 November to 30 April) recorded at the weather station (YZP) at Sandspit, British Columbia, 2000–2013 (n $ 168 in all data sets.) Mean winter Number of days Maximum number temperature temperature of consecutive days Minimum winter Maximum winter Winter (6C) ,0.06C temperature ,0.06 C temperature (6C) temperature (6C) 2000–2001* 5.1 25 1 25.0 12.9 2001–2002 4.2 29 3 25.0 12.8 2002–2003 6.0 10 3 28.3 13.9 2003–2004 5.1 13 1 25.0 15.0 2004–2005 5.4 14 2 26.1 15.0 2005–2006 4.7 28 1 25.6 12.8 2006–2007 4.3 22 2 27.2 11.7 2007–2008* 4.1 11 2 26.1 11.7 2008–2009 3.8 42 2 27.0 13.0 2009–2010 5.1 24 1 215.1 11.6 2010–2011 4.3 35 1 24.8 13.2 2011–2012* 4.0 42 4 212.0 13.5 2012–2013* 5.0 24 1 22.5 13.4 Means 4.7 25 1.7 26.9 13.1 * Incomplete data record. WINTER 2014 BURLES AND OTHERS:WINTER BAT ECOLOGY ON HAIDA GWAII 295

FIGURE 1. Summary of the number of grams of body fat required for a 6 g bat to hibernate in a number of locations on Haida Gwaii, British Columbia. Calculated values are based on temperatures recorded inside a Sitka Spruce snag (HU #1-%); 2 Western Redcedars (HU #2+ HU #3- ) and Huxley cave (D) on Huxley Island; in a Western Redcedar (SI #1 inside-e, under bark-X) and in a Sitka Spruce snag (SI #2-#) near Sandspit; and at YZP (+) as calculated using formulas described in the text. Mean winter temperatures for YZP (—) for the period 2000–2013 are also shown. recorded at the site during summer, were only Island. The adult female, at 7.5 g, appeared to be recorded once during winter, in late April. the only bat that was accumulating fat reserves. Feeding buzzes (attacks on flying insects) were The 2 adult males weighed 5.7 and 5.9 g, while recorded on 12 occasions during all months the juveniles weighed 3.7 to 4.8 g. The 3 adult except November and December. Insects (mostly Little Brown Myotis were the only bats we Lepidoptera: Geometridae, and Diptera: Tipuli- radio-tagged. By following these individuals, dae and Trichoceridae) were also observed on 61 we located 4 day roosts, all in trees. The first occasions during all months. day roost was located on Huxley Island in a Western Hemlock (Tsuga heterophylla) snag directly above a 30- to 40-m-high cliff, about Autumn Roost Activities 150 m inland from the shoreline. The forest was In September 2001, we captured 8 bats: 3 second growth Western Hemlock and Sitka adult (2 M, 1 F) and 4 juvenile (2 M, 2F) Little Spruce (Picea sitchensis), with only a few snags Brown Myotis, and 1 juvenile male Keen’s around the cliff. The second roost was in a tree Myotis at Gandll K’in Gwaayaay and Huxley near the east end of Ramsay Island (52.5776N,

TABLE 4. Summary of acoustic monitoring of bat activities near Sandspit, British Columbia, during the autumn and winter months of 2000–2001 to 2012–2013. Number of Number of Mean (± SD) Number of nights bat Mean (± SD) nights feeding number of nights of Total hours of calls were number of buzzes were feeding buzzes Month monitoring monitoring recorded calls per hour recorded per hour September 3 5.7 3 81.9 ± 70.9 2 12.3 ± 16.6 October 22 99.2 11 7.8 ± 31.9 2 15.4 ± 71.9 November 20 111.1 6 0.2 ± 0.4 0 0 December 12 53.2 0 0 0 0 January 20 81.5 7 4.9 ± 18.1 3 0.6 ± 2.7 February 26 88.2 11 1.9 ± 5.4 3 0 ± 0.1 March 18 62.1 14 2.0 ± 3.0 3 0.1 ± 0.3 April 39 178.8 17 1.5 ± 3.3 1 0 ± 0.1 296 NORTHWESTERN NATURALIST 95(3)

131.3816W). The tree, a large dead Western found that Indiana Myotis (Myotis sodalis) Redcedar (Thuja plicata) with no bark, stood on a experienced overwinter mass losses of up to ridge (approximately 100 m asl). The tree was 32.8%. not obvious from offshore. The third roost was We did record periods when bats would have in a dead Western Redcedar snag (60–70 cm to compensate for below freezing temperatures dbh) on Huxley Island, about 15 m from the in 11 of 16 data sets, but most were of short shoreline. There was no bark, but a crack or duration. Although not common, periodic below- crease ran up the length of the trunk, and the freezing temperatures have been documented in signal from the roosting bat seemed to come caves where Big Brown Bats (Eptesicus fuscus), from fairly high up. At least 2 other snags were Silver-haired Bats, and Townsend’s Big-eared nearby. The fourth roost was in a large (1.5 m Bats (Corynorhinus townsendii), as well as Little dbh; 30 m tall), living Western Redcedar about Brown Myotis, Northern Long-eared Myotis, and 30 m inland from the third roost. The 3 day Eastern Small-footed Myotis (Myotis leibii) hiber- roosts found on Huxley Island were within 300 nated (Brack and Twente 1985; Webb and others to 400 m of the capture location, whereas the 1996; Best and Jennings 1997). A recent study in day roost on Ramsay Island was approximately Alberta also revealed that Big Brown Bats were 4.2 km from the capture site. The third bat that active at temperatures as low as 286C (Lausen we radio-tagged was not relocated after the and Barclay 2006), so wintering bats are not night it was released. We also checked a cave averse to below-freezing temperatures. and a mine adit on Huxley Island but found Perhaps a greater concern for hibernating bats little evidence of use by bats. During September is that temperatures periodically become too 2001, the effect of wind and rain on bat emer- warm, as warm temperatures generally result in gence and activity at Gandll K’in Gwaayaay was higher metabolic rates (although see Speakman evident, with little bat activity on nights of heavy and others 1991; Dunbar and Brigham 2010). rain. This is evident in our calculations of fat requirements, in that our 2 highest estimates DISCUSSION were for winter 2002–2003, the warmest in our Both the results of our monitoring of potential study. Although not taken into account in our hibernation sites and the temperature data model, warm temperatures would also likely obtained from the Sandspit airport support result in more frequent arousals (Twente and our hypothesis that it would be feasible for bats others 1985; Dunbar and Brigham 2010), which to hibernate in trees on Haida Gwaii. Specifi- further increase the amount of fat required to cally, temperatures we recorded in trees were survive winter. One trade-off of warm temper- well within the range of optimal hibernaculum atures would be that insects may become active, temperatures predicted by Humphries and thereby creating foraging opportunities for bats. others (2002); they were also similar to those Another is that energy could be saved if documented in bat hibernacula on Vancouver arousals are timed to coincide with warming Island (Mather and others 2000). temperatures. The results of our calculations of energy Another concern for a bat hibernating in our requirements also support our hypothesis that study trees would be the greater temperature a bat could hibernate inside our study trees. fluctuations it would experience as compared to a Specifically, our estimates of fat reserves re- subterranean hibernaculum. While Davis and quired for a bat to survive a winter were well others (2000) reported stable temperatures with within the limits of the 1.5 to 3.5 g of fat reserve variances of only 0.02 to 0.246Cathibernaculaon predicted to be needed by Humphries and Vancouver Island, we calculated variances gener- others (2002). These estimates amount to 29.3 ally of 2.5 to 4.46C for temperatures inside our to 32.7% of pre-hibernation body mass, which, study trees, and 6.1 to 7.66C under the bark. These while higher than the 25% reported by Fenton fluctuations could also result in more frequent (1970), is remarkably similar to Kunz and others arousals, which would represent an added (1998) estimates of 29.6 to 32.9% mass gain in energetic cost for a bat hibernating in a tree. autumn for Little Brown Myotis in Vermont. In Our finding of California Myotis in the a similar species, Johnson and others (1998) vicinity of Sandspit during all winters that we WINTER 2014 BURLES AND OTHERS:WINTER BAT ECOLOGY ON HAIDA GWAII 297 monitored provides evidence that this species Falxa 2007). Of the 4 species found on Haida was not hibernating in caves or mines given that Gwaii, this is the only species that is likely to be the nearest underground mine and the nearest capable of migrating off the islands. known cave are approximately 100 and .40 km The fact that insects were active during away, respectively. California Myotis were also winter indicates that there were likely opportu- the only species for which a winter specimen nities for bats to forage and replenish their fat was collected. Thus, these bats were likely reserves during periodic arousals. Although roosting in nearby trees or buildings. This is there did not appear to be any clear correlation not surprising, as they have previously been between insect presence and bat activity, forag- identified as being active during winter elsewhere ing ‘‘buzzes’’ were recorded on 5 nights when in British Columbia (Nagorsen and others 1993) insects were also observed. Stomach contents of and western Washington (Falxa 2007). the single California Myotis collected in winter Little Brown Myotis were relatively common included 1 winter cranefly (Diptera: Trichocer- throughout summer and into autumn, but they idae), evidence that it had been foraging. While were not acoustically detected at all between active foraging would increase fat depletion, it late October and late April. This result is similar could also allow for further fat accumulation if to what has been found in southeastern Alaska, insects were abundant. where radio-tagged Little Brown Myotis disap- While our study has demonstrated that it is peared in late October (K Blejwas, Alaska feasible for bats to hibernate in trees on Haida Department of Fish and Game, pers. comm.), Gwaii, our efforts to determine where they were possibly suggesting that they migrate some- actually hibernating were less successful. Our where on or off the islands to hibernate. acoustic evidence suggests that California Myo- Our efforts to track radio-tagged Little Brown tis are wintering either in trees or in buildings Myotis to their hibernacula failed, in large part around Sandspit. The other 3 species found on because we started too early in the season. We Haida Gwaii seem to disappear in autumn, assumed that by early September they would be however, suggesting that they may be migrating to a hibernaculum. Given the serious negative migrating towards their hibernaculum, where impact that white-nose syndrome is having on they would swarm and mate before entering eastern populations of hibernating bats, deter- hibernation. What we found was that by late mining where the bats of Haida Gwaii over- September radio-tagged bats had not moved winter is a critical component in planning for any distance from where they were captured their protection. We recommend that all known and were still using trees as roosts. We also caves and mines be investigated in winter for found that only 1 of the 3 adults that we the presence of bats, and that further radio captured had begun to accumulate fat reserves. telemetry studies be carried out to determine None of the 5 juveniles captured had accumu- where bats are roosting in late autumn. lated any fat reserves, but juveniles generally begin this process much later than adults (Kunz ACKNOWLEDGMENTS and others 1998). Because the weather was deteriorating, and foraging opportunities were We thank World Wildlife Fund (Canada) and becoming rarer, we expected that bats would be Environment Canada for their support through the in the latter stages of preparation for hiberna- Endangered Species Recovery Fund, and Gwaii Haanas National Park Reserve and Haida Heritage tion by late September. Our investigation of Site for providing logistical support for our research. potential underground hibernacula at this time The work was also supported by Research and also failed to find any bats. Equipment Grants from the Natural Sciences and The almost complete absence of winter Engineering Research Council (Canada) to RMRB, records of Keen’s Myotis is not unexpected. It RMB and MBF. We thank T Jung, K Blejwas and an is not a common bat on Haida Gwaii, and its anonymous reviewer for comments on a previous low intensity echolocation call is not easily draft of this manuscript. recorded. 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* Unpublished.