Powerhouse Restoration Site Small Mammal Trapping Fall 2010 and Summer 2011

Transcription

1 Powerhouse Restoration Site Small Mammal Trapping Fall 2010 and Summer 2011 Prepared for: Lillooet Naturalists Society PO Box 2171 Lillooet, BC V0K 1V0 Prepared by: Dustin Oaten, MSc., RPBio. 333 Hollyburn Drive Kamlooops, BC V2E 1Y9 i

2 TABLE OF CONTENTS INTRODUCTION... 1 METHODS... 2 SITES... 2 TRAPPING... 4 RESULTS... 5 DISCUSSION... 6 MANAGEMENT RECOMMENDATIONS... 7 COARSE WOODY DEBRIS... 7 TRAPPING... 7 WESTERN SCREECH OWL SURVEYS... 8 LITERATURE CITED... 9 ii

3 LIST OF TABLES AND FIGURES Figure 1. Map of study site and location of trapping grids. Please note that the Reference and Restoration grids were configured as 8 x 8 trapping grids (1.03 hectares) while the Riparian grid was 16 x 4 in 2010 (0.95 ha) and 3 x 21 (0.88 ha) in 2011 due to the nature of the riparian area (0.95 hectares).3 Table 1. Descriptive statistics for small mammals within the three grids at the Powerhouse Restoration site iii

4 INTRODUCTION The Lillooet Naturalists Society, in partnership with Cayoose Creek St'at'imc and other interested parties, are working on a Powerhouse Foreshore Restoration project which is aimed at mitigating site damage caused by the construction and operations of the BC Hydro Seton Dam and Cayoosh Creek Canal complex. The aim of the restoration project is to create a more diverse and healthy habitat for wildlife, with a special focus on species-at-risk, at the confluence of the Seton and Fraser Rivers. Activities with the restoration area have included deactivating old roadbeds, mounding the site to increase habitat complexity, placing coarse woody debris and standing snags, removing invasive plant species and planting with native trees, shrubs, herbs and grasses that have been propagated in the nursery established for the restoration project. The Lillooet Naturalist Society has also incorporated flora and fauna studies and related monitoring into the restoration program. As part of the monitoring program, a Western Screech Owl (Otus kennicottii macfarlanei subspecies) was identified (Jared Hobbs, Ministry of Environment) as occurring within the project area (within the riparian area immediately adjacent to the Fraser River). This was a significant observation because the Western Screech Owl is provincially red-listed by the Conservation Data Center and is listed as endangered by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC 2002). As the restoration project is aimed, in part, at restoring the site for all wildlife species, this find creates a dual opportunity to quantify both the availability of prey items for the Western Screech owl as well as to identify the current distribution and diversity of small mammals. The Western Screech Owl appears to be opportunistic in its choice of prey with their diet including various species of small mammals, fish, birds, insects and other invertebrates. The small mammal component of their diet is of particular interest for this restoration site as small mammals have been identified as important components of faunal communities. Small mammals contribute to the biodiversity and the functioning of North American temperate forest ecosystems (Carey and Johnson 1995). They are important as prey for terrestrial and avian predators (Carey and Harrington 2001), distributors of 1

5 mycorrhizal fungi (Maser et al. 1979), seeds, spores and propagules of vascular plants, bryophytes, fungi, and lichens (Carey and Harrington 2001), and as consumers of invertebrates (Elkinton et al. 1996) and plants (Sullivan et al. 2000). Small mammal activity mixes the soil and decomposes organic matter and litter (Bowman et al. 2000). Many authors have suggested that they may be a useful bioindicator for assessing regional biodiversity because of their predominate role within ecosystems and because they serve as prey for a variety of species (Carey and Harrington 2001). The intention of this project was to quantify the populations and diversity of small mammals within three distinct habitats within the Powerhouse Restoration Area the current restoration area, the riparian area in which the Western Screech owl was located, and a Ponderosa pine (Pinus ponderosa) referenced area. This quantification is also intended to serve as a baseline for future trapping sessions as well as for quantifying the availability of potential prey items for the Western Screech Owl. In addition, it was intended to gain an understanding as to how the restoration site small mammal community compares to that of adjacent sites. Trapping has occurred in the fall of 2010 and the summer of METHODS TRAPPING GRIDS Three distinct areas were identified during a reconnaissance survey with members of the Lillooet Naturalists Society the Restoration grid, Riparian grid, and the Reference grid (Figure 1). Each of these areas was significantly different in terms of the forest type and or stage of restoration. The Restoration grid is currently being restored from what was essentially a compacted gravel landscape to an area in which the gravel has been removed, soil has been reclaimed, native plants have been planted, and coarse woody debris incorporated including snags. The Riparian grid is a moderately dense habitat dominated by shrubs and other deciduous trees. This area is a narrow strip located between the Fraser River and an upland Ponderosa pine stand. The Reference grid is located within a Ponderosa pine dominated site with a healthy occurrence of mostly native shrubs, grasses, and forbs. 2

6 RIPARIAN GRID 2010 and 2011 RESTORATION GRID REFERENCE GRID Figure 1. Map of study site and location of trapping grids. Please note that the reference and restoration grids were configured as 8 x 8 trapping grids (1.03 hectares) while the riparian grid was 16 x 4 in 2010 (0.95 ha) and 3 x 21 (0.88 ha) in 2011due to the nature of the riparian area (0.95 hectares). 3

7 TRAPPING Small mammals were sampled within 8 x 8 trapping grids within the Restoration and Reference grids (1.03 hectares) and a 16 x 4 grid was within the Riparian grid (0.95 hectares) in 2010 the Riparian grid was reconfigured to 3 x 21 (0.88 ha) (with an additional trap added) due to the Fraser River being at unusually high water in Inter-trap spacing was 14.5 m on all grids. Each study grid was trapped using Longworth-style live-traps (Little Critter Traps, Rogers Manufacturing, Kelowna, BC). Prior to the trapping session, traps were prebaited once with a mixture a small amount of whole oats and sunflower seeds, and left open and unattended for about two weeks. Following the prebaiting session, small mammals were live trapped for three consecutive nights (October 25-27, 2010 and June 16-18, 2011) using the same mixture of oats and seeds, plus a slice of apple for water intake. Fresh bedding (moisture-wicking synthetic cotton) was provided in each trap. Trapped animals were identified to species and sex, weighed using a Pesola spring balance and classified as either a juvenile or adult. Deer mice (Peromyscus maniculatus) were classified as juveniles if their body mass was < 15g (Fairbairn 1977). As the trapping was intended to be a brief examination of the current small mammal community we used permanent markers to individually identify each animal in A systematic system of body location and colour was applied to each animal such that all animals were uniquely identifiable. Issues associated with identifying these marks during the third night of trapping in 2010 prompted us to use individually numbered Monell #1 ear tags in After each animal was marked they were released at the point of capture. DATA ANALYSIS Small mammal density estimates were calculated from mark recapture data using Program CAPTURE (Otis et al. 1978). The model that was automatically selected in this program was used for each density estimates. These density estimates then were converted to animals/ha based on the individual grid sizes. Trapping success (animals/trap night) also was calculated for each trapping session this accounted for the unequal number of traps used and served as an additional abundance estimate. 4

8 RESULTS The only species captured during both the 2010 and 2011 trapping sessions was the ubiquitous deer mouse. A total of 91 individual animals were marked within the three trapping grids in 2010 and 99 animals in with the highest number occurring within the Riparian Site in both years (see Table 1 for an overview). The Reference Site had both the fewest number of captures as well as the fewest number of individuals for both trapping sessions. The sex ratios were within normal ranges for both the Reference and Riparian grids but were heavily skewed towards males within the Restoration grid in 2010 this was corrected in Trapping effort and densities were twice as high within the Riparian grid as compared to the other sites. Table 1. Descriptive statistics for small mammals within the three grids at the Powerhouse Restoration site for 2010 and Restoration Riparian Reference Restoration Riparian Reference Grid Grid Grid Grid Grid Grid Trapping Effort (animals/trap night) Mean Male Weight (grams) Mean Female Weight (grams) Total No. Individual Animals No. of Individual Males No. of Individual Females Adults Juveniles Density (animals/ha) 36 ± ± ± ± ± ± 1.5 5

9 DISCUSSION Many small mammal species are subject to cyclic population fluctuations that are characterized by a regular period (the interval between successive density peaks) and highly variable amplitude (the ratio of maximum to minimum population) (Korpimaki and Krebs 1996). The mechanisms driving these long term fluctuations remain unknown as are the density dependent or density independent factors that influence annual fluctuations (Yahner 1992). As these fluctuations are know to occur, there is a significant probability that other endemic small mammals may still occur within the project area outside of thee deer mouse. Other species that may occur within the project area include the southern red backed vole (Clethrionomys gapperi), long tailed (Microtus longicaudus), montane vole (Microtus montanus), meadow vole (Microtus pennsylvanicus), Northwestern Chipmunk (Tamias amoenus), and several Sorex spp. they may occur in small numbers and subsequent trapping sessions may pick these species up. The Reference grid had the lowest number of total captures as well as the fewest individuals captured the 2011 trapping session maintained the same pattern. This was surprising given that the site is composed of a mature, moderately healthy, Ponderosa pine stand with a well-developed shrub, grass, and forb understory community. In addition, the site also supports a large volume of coarse woody debris. Thus the low density was surprising and mostly unexplainable. A repeated sample, over time and across seasons, may be appropriate to confirm the trends that were identified during these trapping sessions. Another interesting result was the heavily skewed sex ratio (towards males) within the Reference grid. This may have been due to the lower habitat quality with some areas currently being restored and not having any cover for security and little in the way of food items. As this area is re-vegetated the probability of small mammal use will be high. The fact that there are endemic small mammals within this area is a good sign for the positive impact of the restoration activities. The trapping in 2011 showed an increase in the density of deer mouse as well as an increase in the number of females. Continued monitoring would be prudent to track the change in small mammals within this site over time. 6

10 The Riparian grid supported the highest density of small mammals over both of the other grids. Given the diversity of this habitat, its vigorous shrub community, and the fact that most riparian areas support diverse faunal communities, this was not surprising. However, the fact that only a single small mammal species was captured was surprising. Again, this suggests that a repeated sample, over time and across seasons, may be appropriate to confirm the trends that were identified during this session. Each of the trapping grids appeared to be more productive in 2011 with more females showing signs of reproduction and a higher proportion of juveniles within the deer mouse populations. The Riparian grid was still the more productive site with more total animals, more females, and a higher proportion of juveniles within the population. Future trapping sessions may aid in tracking the changes in population structure over time even a single annual trapping event may provide for consistent information that can be tracked over time. This information may be used to understand how the restoration activities are working to improve the local habitat for small mammals. MANAGEMENT RECOMMENDATIONS COARSE WOODY DEBRIS The Lillooet Naturalists Society has made a strong attempt to add coarse woody debris to the restoration area and should continue to do so. The key is to ensure that large debris are incorporated, trees at least 30 cm DBH and 10 meters in length, as larger debris provide better habitat for small mammals. In addition, small debris piles can be created within the site if required as an additional habitat feature. For future restoration activities, incorporating 2 10 large woody debris per hectare would be a good target to add to small mammal habitat features within the area. The use of debris piles have been shown to increase small mammal populations (Sullivan et al. 2011). TRAPPING Both trapping events only yielded a single species, the ubiquitous deer mouse, as such it would be important to incorporate further trapping events to further identify and quantify the occurrence of small mammals within the three different grids. This would also help to confirm the trends that were identified during this trapping session. 7

11 WESTERN SCREECH OWL SURVEYS As Western Screech Owls are a species identified as at-risk, it would be important to complete frequent, though non-invasive, surveys to track to occurrence of this species within the project area. These surveys would be simple playback surveys which are used to elicit a response from a species. If the species remains within the project area, it would be important to identify nest and day roost sites and any breeding events. Once roost sites are identified, pellets could be collected and analyzed to identify prey items. This recommendation still remains as good potential tool for gaining information on the occurrence of this species within the project area. 8

12 LITERATURE CITED Bowman, J. C., D. Sleep, G.J. Forbes., and M. Edwards The association of small mammals with coarse woody debris at log and stand scales. Forest Ecology and Management. 129: Carey, A.B., and M.L. Johnson Small mammals in managed, naturally young, and old-growth forests. Ecological Applications. 5(2): Carey, A.B., and C.A. Harrington Small mammals in young forests: Implications for management for sustainability. Forest Ecology and Management. 154: COSEWIC Assessment and update status report on the Western Screech Owl (Otus kennicottii) in Canada. Elkinton, J.S., W.M. Healy, JP. Buonaccorsi, G.H. Boettner, A.M. Hazzard, H.R. Smith., and A.M. Libhold Interactions among gypsy moths, white-footed mouse, and acorns. Ecology. 77: Fairbairn, D.J Why breed early? A study of reproductive tactics in Peromyscus. Canadian Journal of Zoology. 55: Maser, C., R. Anderson, K. Cromack, J.T. Williams., and R.E. Martin Dead and downed woody material. In. Thomas, J.W. (Ed.), Wildlife habitats in managed forests: the Blue mountains of Oregon and Washington. USDA Agricultural Handbook 553. pp Otis, D.L., K.P. Burnham, G.C. White., and D.R. Anderson Statistical inference from capture data on closed animal populations. Wildlife Monographs. 62: Sullivan, T.P., D.S. Sullivan., and P.M.F. Lindgren Small mammals and stand structure in young pine, seed-tree, and old-growth forest, southwest Canada. Ecological Applications. 10: Sullivan, T.P., D.S. Sullivan., and P.M.F. Lindgren Partial harvesting of dry Douglas-fir forests: stand structure, range habitats and maintenance of biodiversity using small mammal indicators. Forestry. 84(3):

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