Vol. 15, No. 4 A Population Crash of the Red-backed Vole (Myodes gapperi) in Nova Scotia Inferred from Bycatch of the Long-tailed Shrew (Sorex dispar) Aaron B.A. Shafer1,2,* and Donald T. Stewart2 Abstract - In 2006, we collected two Sorex dispar (Long-tailed Shrew) specimens from Mac- Donald Pond, NS, Canada, which is a range extension of this elusive species. Trapping data revealed significantly lower numbers of Myodes (= Clethrionomys) gapperi (Red-backed Vole) bycatch than expected based on previous studies. Red-backed Voles are the most common rodent found in Nova Scotia forests. Here we report an apparent population crash of Red-backed Voles in Nova Scotia, along with a closer examination of a Cape Breton Island population. Sorex dispar Batchelder (Long-tailed Shrew) is considered an Appalachian species occupying appropriate habitat from Tennessee/North Carolina to mainland Nova Scotia (Kirkland 1981, Kirkland and Van Deusen 1979). Recent trapping efforts (i.e., Shafer and Stewart 2006) suggested that the Long-tailed Shrew might have a larger distribution in Atlantic Canada than previously thought. In August 2006, trapping expeditions were conducted at MacDonald Pond, Hants County, NS (44°52'59"N; 64°12'59"W); and the Grand Anse Valley, Cape Breton Highlands National Park, NS (46°48'48"N; 60°44'10"W). The trapping was part of a larger effort to obtain specimens of the Long-tailed Shrew species complex (see Rhymer et al. 2004). Both sites were comprised of deciduous forest, with rocky (talus) substrate, rotting logs, and moss being the major habitat components. We collected two Long-tailed Shrews from MacDonald Pond, NS. This finding is the southern-most location identified for this species in Canada (Fig. 1), and brings the total number of Canadian records to Notes of the Northeastern Nat u ral ist, Issue 15/4, 2008 626 Figure 1. Recorded northeastern localities for species of Sorex dispar complex. Highlighted trap sites are: MacDonald Pond (NS; 44°52'59"N; 64°12'99"W) in bottom left; and the Grand Anse Valley (46°48'48"N;60°44'10"W) in bottom right. Topographic maps courtesy of Natural Resources Canada. 2008 Northeastern Naturalist Notes 627 21 (see Shafer and Stewart [2006] for complete list). The high trap success rate (0.25 captures per 100 trap nights; Table 1) at MacDonald Pond for the Long-tailed Shrew relative to other trapping expeditions in Nova Scotia (e.g., Shafer and Stewart 2006, Woolaver et al. 1998) is worth discussing. Talus slopes are the preferred habitat of the Long-tailed Shrew; however, they are often overlooked in small-mammal surveys. One reason for this is that pitfall traps are difficult to place in the rocky substrate, requiring a concerted trapping effort. Given our trapping success, we feel that the Long-tailed Shrew is likely more widespread throughout Nova Scotia and Atlantic Canada, although probably at low densities. Through a total of 798 trap-nights (416 Victor snap trap, 382 pitfall) at MacDonald Pond and 1766 trap-nights (740 Victor snap trap, 1026 pitfall) in the Grand Anse Valley, two and one specimen(s) of Myodes (= Clethrionomys; Carleton et al. 2003) gapperi Pallas (Southern Red-backed Vole) were collected as bycatch, respectively. In the absence of a controlled population-density study, trap-night success can be used as an index of abundance (Herman and Scott 1984). Comparing our Red-backed Vole snap-trap bycatch to similar trapping efforts targeting Long-tailed Shrews in Nova Scotia and New Brunswick (Table 2), it is evident our success per 100 trapnights is markedly lower (G-test of independence, G = 29.9, P < 0.001). Variation in Table 1. Small-mammal captures from August 2006 on MacDonald Pond and Grand Anse Valley, Nova Scotia. PF = pitfall trap, ST = snap trap, and TN = trap night. Captures on Captures on the Macdonald Pond Grand Anse Valley Species Common name (416 PF, 382 ST) (1026 PF, 740 ST) Blarina brevicauda Short-tailed Shrew 2 (0.25/100 TN) 22 (1.3/100 TN) Sorex cinereus Masked Shrew 7 (0.88/100 TN) 43 (2.4/100 TN) Sorex dispar/gaspensis Long-tailed Shrew complex 2 (0.25/100 TN) 2 (0.11/100 TN) Sorex fumeus Smokey Shrew 45 (5.6/100 TN) 0 (0/100 TN)* Sorex hoyi Pygmy Shrew 0 (0/100 TN) 3 (0.17/100 TN) Microtus chrotorrhinus Rock Vole 0 (0/100 TN) 1 (0.06/100 TN) Myodes gapperi Red-backed Vole 2 (0.25/100 TN) 1 (0.06/100 TN) Napaeozapus insignis Woodland jumping Mouse 2 (0.25/100 TN) 7 (0.40/100 TN) Peromyscus maniculatus Deer Mouse 0 (0/100 TN) 8 (0.45/100 TN) *No species records on Cape Breton Island, NS, Canada. Table 2. Myodes gapperi (Red-backed Vole) snap trap captures on rocky deciduous coniferous forests in Nova Scotia (NS) and New Brunswick (NB), Canada. TN = trap-night. No. of voles / snap TNs Year (per 100 TN ) Locality of study Reference 1 / 740 (0.14) Grand Anse Valley, NS 2006 This study 2 / 416 (0.48) Macdonald Pond, NS 2006 This study 14 / 900 (1.6) Stewart Mtn., NS 2005 Shafer and Stewart 2006 5 / 100 (5) Nerepis Hills, NB 2002 McAlpine et al. 2004 21 / 1799 (1.2) Smith Brook, NS 1986 Scott and Van Zyll de Jong 1989 21 / 1478 (1.4) Folly Mtn, NS 1984 Scott 1987 92 / 5699 (1.6) NS and NB (10 localities) 1978/1979 Kirkland and Schmidt 1982 8 / 306 (2.6) Albert County, NB 1978 Kirkland et al. 1979 73 / 500 (14.6) Grand Anse Valley, NS 1974 Roscoe and Majka 1976 628 Northeastern Naturalist Notes Vol. 15, No. 4 trapping success can be attributed to loss of bait; however, this was not likely a factor because our traps were checked twice daily and bait reapplied as necessary. The Grand Anse Valley site is the same location that was previously trapped by Roscoe and Majka (1976) in August of 1974 (see Prescott et al. 1979; C. Majka, Nova Scotia Museum of Natural History, Halifax, NS, Canada, pers. comm.). The survey conducted by Roscoe and Majka (1976) yielded 73 Red-backed Voles in a total of 500 snap trap-nights. Our collection rate of a single Red-backed Vole in 740 snap trap-nights is nearly 100 times lower than Roscoe and Majka (1976), and suggests a population crash (G = 129.8, P < 0.001). Such a low number of captures is surprising as peaks in population density typically take place during late summer (Merritt 1981) when trapping occurred. Furthermore, Herman and Scott (1984) trapped throughout Cape Breton Island and mainland Nova Scotia and found Red-backed Voles to be the most abundant bycatch species (8.58 and 2.95 captures per 100 trap-nights). Small-mammal bycatch data can be a useful measure of the local community composition. Red-backed Voles of the genus Myodes are among the most common small mammals throughout the Holarctic region. The Southern Red-backed Vole has a Nearctic, primarily Canadian, distribution. In Nova Scotia, Red-backed Voles may be the most abundant forest rodent (Scott and Hebda 2004), occurring in deciduous, coniferous, and mixed forests (Merritt 1981). The Red-backed Vole is an opportunistic, omnivorous feeder that often relies on seeds as a food source in the winter (Merritt and Merritt 1978, Merritt 1981). Accordingly, the Red-backed Vole in Maine has demonstrated cyclic population dynamics that correspond to Pinus strobus L. (Eastern White Pine) seed fall (Elias et al. 2006). Mid-winter conditions are critical to the reproductive success and survival of the Red-backed Vole (Fuller et al. 1969). In particular, because Red-backed Voles do not enter torpor, it often relies on low-quality food during the winter (Fuller et al. 1969). The forest at the Grand Anse Valley site consists mainly of Betula alleghaniensis Britt (Yellow Birch), which is not a mast-seed producer. It is therefore unlikely that seeds make up a large portion of the Grand Anse Valley’s Red-backed Vole winter diet. More likely, the opportunistic feeding of Red-backed Voles suggests a climatic or epizootic explanation for the crash. Because bycatch numbers of other species are relatively consistent with the data from Roscoe and Majka (1976), a species-specific disease may be the cause. For example, the bycatch number of Napaeozapus insignus Miller (Woodland Jumping Mouse) in our study did not significantly differ from that reported by Roscoe and Majka (1976) (G = 1.04, P = 0.31). Herman and Scott (1984) observed a similar trend in Nova Scotia when studying Peromyscus maniculatus Wagner (Deer Mouse). In that study, Deer Mice numbers throughout mainland Nova Scotia crashed while an insular island population remained constant, suggesting an epizootic outbreak (Herman and Scott 1984). Concerted annual trapping in a variety of habitats may be required to more precisely track the incidence of disease, abundance, and distribution of these vole populations. Additional trapping studies combined with necropsies are required to elucidate the cause(s) of the apparent crash of Nova Scotia’s Red-backed Vole populations. Acknowledgments. Trapping efforts were funded by the Natural Sciences and Engineering Research Council of Canada (grant 217175 to D.T. Stewart), New Brunswick Wildlife Trust Fund, and the Atlantic Centre for Global Change and Ecosystem Research at Acadia University. The Cape Breton Highlands National Park provided in-kind support. Special thanks to John Gilhen, Andrew Hebda, Fred Scott, Lily Stanton, David Stanton, Nathan Stewart, and Lauren McCarville for their help trapping. Thanks to Michael Peckford and the two anonymous reviewers for their comments on the manuscript. 2008 Northeastern Naturalist Notes 629 Literature Cited Carleton, M.D., G.G. 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