Sheep on Ewin Ridge, February 2010; Photo: I. Teske Habitat use, seasonal movements, and population dynamics of bighorn sheep in the Elk Valley Prepared for: BC Ministry of Forests, Lands and Natural Resource Operations 205 Industrial Road G. Cranbrook, BC V1C 7G5 and Teck Coal Limited P.O Box 2003 Sparwood, BC V0B 2G0 Prepared by: Kim G. Poole Aurora Wildlife Research 1918 Shannon Point Road, Nelson BC V1L 6K1 Tele. (250) 825-4063; e-mail: [email protected] May 2013 Elk Valley bighorn sheep project Executive summary Winter is a critical season for most mountain ungulates, which use a variety of strategies to cope with burial of preferred forage and increased cost of locomotion in snow. Rocky Mountain bighorn sheep (Ovis canadensis canadensis) inhabit the east side of the Elk Valley in southeastern British Columbia where forestry and 4 large, open-pit coal mines are in operation. Sheep in this area generally winter at high elevation on windswept, south-facing native grasslands, with some sheep also wintering on mine properties. Expansion of coal mining is proposed in portions of the valley which may result in direct loss of high-elevation winter range, which in some instances can result in the creation of winter habitat through reclamation of mine disturbance. Winter range may be the single most important factor limiting sheep populations in the area. The primary objectives of this study were to describe seasonal movements, winter habitat selection, and use of mine properties by this population. A concurrent companion study examined winter range plant communities and plant production, range condition, and winter diet. We obtained ~54,000 GPS locations from 41 sheep (19 ewes, 22 rams) between March 2009 and May 2011. Winter severity differed markedly between winter 2009-10 (very low snow) and winter 2010-11 (deep snow). Survival of collared sheep dropped from 0.93 (annual rate) during the first year to 0.78 during the second, more severe winter. Summer and winter range sizes did not differ between sexes, but was roughly one-third the size during winter 2010-11 (3.2 km2) compared with winter 2009-10 (9.5 km2). Most (79%) of the sheep monitored for a summer to winter season were migratory (non- overlapping seasonal ranges), and all non-migratory sheep – mostly ewes – were associated with the northern 2 adjacent coal operations. Fidelity to winter ranges among years was high and equal between sexes (88%); some segregation of ranges between sexes was apparent. Although differences among individuals and mine areas were apparent, use of mine properties by the population varied seasonally, and showed low use (~10–18%) between November-December and April, followed by increased use to peak at about 60–65% in September-early October. We used a 2-stage approach to examine habitat selection, by first modelling individuals using Resource Selection Function analysis (multivariate logistic regression) and then by averaging parameter estimates across individuals. We examined resource selection at 2 scales: winter use to home range and within the winter range. Selection at both scales was dominated by terrain variables, with slightly less influence by cover class variables. There were limited differences in use and selection between sexes. At both home range and winter range scales, wintering sheep were positively associated with high elevations, shorter distance to escape terrain, and warmer aspects (solar duration). Terrain ruggedness was not a strong variable in models. Relative to coniferous forests (strongly avoided by all individuals), high-elevation, native grasslands (combined with exposed lands for modelling) was the highest ranked cover class at both home and winter range scales. The industrial cover class (mine-altered properties) was ranked lower in importance compared with high-elevation grasslands. We used 2006-11 mine and government survey data for independent model validation; fit of the winter range model was very high (rs = 1.00). All mine properties showed areas of high probability winter range, yet only Greenhills Operations and the South Pit area of Elkview Operations had significant use during winter. Most sheep that used mine properties during winter used reclaimed habitats, primarily reclaimed spoils and pits. Aurora Wildlife Research Page ii Elk Valley bighorn sheep project We identified lambing areas using collar data from 18 ewes and 31 ewe-years. Median date of lambing was 19 May in 2009 and 26 May in 2010. For both years combined, 60% of estimated births occurred between 19-27 May (full range 10 May – 4 June). Of 31 lambing areas, 13 (42%) were on active mine properties of the 3 northern mines. Fidelity to lambing areas was high. When compared to native habitats, lambing areas on mine properties were at significantly lower elevations, on shallower slopes, further from escape terrain, and with lower proportions of conifer, shrub, both types of grasslands, and rock-rubble cover classes, and higher proportions of industrial cover class. Ewes that lambed in native areas selected more strongly for warmer aspects and higher proportion of conifer cover and high- elevation grasslands than ewes that lambed in mine areas. Ewes that lambed on mine properties selected more strongly for more rugged slopes. Rutting occurred through the study area, primarily on winter ranges and mainly in native habitats; 28% of rutting locations were on mine properties. Fidelity to rutting areas varied between years. We conducted sheep surveys of the study area in February 2010 and 2011, using collars to obtain an indication of sightability. Accounting for a sightability of 0.82, 645 sheep (90% CI 580–772) were estimated within the study area in 2010. In 2011, lower sightability (0.77) and fewer sheep observed resulted in an estimate of 555 sheep (90% CI 485–687). Bighorn sheep utilize a range of native and mine-altered habitats to varying degrees at different times of the year. Use of mine properties by this population is high during the growing season, which may have contributed to the observed population increase since the late 1980s, likely aided in large part through reclamation. Greater winter severity appeared to result in reduced winter range size and increased mortality, attesting to the importance of this season to sheep ecology. Considering winter distribution and population counts, Ewin Ridge had by far the highest wintering population, and Gill Peak, Brownie, and Ewin Ridge had the highest densities of sheep. Management to enhance sheep habitat could include controlling forest encroachment on seasonal ranges and movement corridors. On mine properties, sheep habitat can be developed by providing escape terrain adjacent to high quality forage and considering landform design (i.e., steep south-facing aspects where wind modeling could predict snow free potential) as an integrated component of mine design when bighorn sheep are a target species for reclamation activity. However, successful use of these areas during winter likely depends on snow depths and forage availability. Further surveys could be conducted to examine the relative demographic fitness of sheep wintering on native versus mine- altered habitats. Balancing sheep and elk numbers on winter ranges will be an important component of wildlife and habitat management. Main winter ranges comprise 2.7% of the study area (4.3% of the merged annual sheep ranges), emphasizing the limited amount of occupied winter ranges within the landscape. In addition to sheep grazing pressure, the number of elk on native sheep winter ranges during both summer and winter may already be negatively influencing range quality in some locations and could negatively influence other ranges. High fidelity to winter ranges and the apparent influence of winter severity on survival suggest that disturbance to native winter range resulting from development should be minimized or be conducted in a manner that effectively manages and/or mitigates the impacts. Large scale removal of main native winter ranges would likely result in a population decline and should be avoided. Aurora Wildlife Research Page iii Elk Valley bighorn sheep project Table of Contents Executive summary ....................................................................................................................................... ii Glossary and acronyms ................................................................................................................................. 1 Introduction .................................................................................................................................................. 2 Study area ..................................................................................................................................................... 6 Study design and methodology .................................................................................................................... 9 Bighorn sheep capture and collaring ........................................................................................................................ 9 Collar data handling ................................................................................................................................................ 11 Fate and survival rates ............................................................................................................................................ 12 Seasonal ranges ......................................................................................................................................................