Garth Mowat

Estimating population size of grizzly bears using hair capture, DNA profiling, and mark-recapture analysis

We used DNA analysis to estimate grizzly bear (Ursus arctos) population size in a 9.866-km 2 area in southeast British Columbia and a 5,030-km 2 area in southwest Alberta. We sampled bears by removing hair at bait sites surrounded by a single strand of barbed wire. DNA profiling with microsatellites of the root portion of the hair was used to identify individuals. We collected hair from 109 different bears and had 25 recaptures in 5 10-day trapping sessions in British Columbia. In Alberta we collected hair from 37 bears and had 9 recaptures in 4 14-day sessions. A model in program CAPTURE (M h ) that acconmodates heterogeneity in (individual capture probaluilities estimated the population size in British Columbia as 262 (95% CI = 224-313) and in Alberta as 71 (60 100), We believe that hair capture combined with DNA profiling is a promising technique for estimating distribution and abundance of bears and potentially many other species. This approach is of special interest to management biologists because it can be applied at the scale conservation and management decisions are made.

Estimating marten Martes americana population size using hair capture and genetic tagging

We tested non-invasive genetic methods for estimating the abundance of marten Martes americana using baited glue-patch traps to pull hair samples from individual animals. We divided our 800–km2 study area into 3 × 3 km cells and put one hair trap in each cell. We trapped 309 sites for an average of 15 days each between 15 January and 14 March 1997. Based on tracks in snow and hair morphology, we captured hair from marten, red squirrels Tamiasciurus hudsonicus, flying squirrels Glaucomys sabrinus, short or long-tailed weasels Mustela erminea and M.frenata, and several unidentified mouse and vole species. Of 309 sites, 58% collected a marten hair sample while 8% of sites removed weasel hair. When roots were embedded in adhesive, a xylene wash was used to remove them before extracting DNA. All marten samples were genotyped at six microsatellite loci to identify individuals. Xylene-washed samples yielded similar genotyping success to samples that had never been exposed to xylene, and genotyping success increased with the number of hairs in the sample. Genetic data allowed 139 samples to be assigned to 88 individual marten, constituting 124 capture events during the four trapping sessions. The population estimate for our study area was 213 (95% Cl: 148–348) and the average capture probability was 0.15. The density of marten in our study area was 0.33/km2 when inhospitable habitat was removed from the calculation. We believe hair sampling and genetic analysis could be used to measure population distribution, trend and size for marten, and perhaps also for other carnivores.

Lynx population dynamics in an untrapped refugium

Refugia from trapping are believed to be important to support a long-term sustainable harvest of Canada lynx (Lynx lynx), but long-term studies in unharvested areas are lacking. We studied lynx population characteristics in relation to snowshoe hare (Lepus americanus) densities in a 301 km 2 refugium in the Yukon Territory between 1986 and 1994. Lynx carcasses were collected from adjacent trapping concessions for analysis of attributes of the harvested population. Hare density peaked in summer 1990 and began to decline in the winter of 1990-91. Lynx density in March varied with hare density from 2.7/100 km 2 in 1987 to 44.9/ 100 km 2 in 1991-92. The lynx population doubled annually for 4 years when reproduction and kit and adult survival were high, and immigration balanced or exceeded emigration. High mortality and emigration characterized the lynx decline. Proportions of breeding adults were 100% most years, including the first year of declining hare densities, but zero in the following 2 years. Yearling females reproduced only in the 2 years of highest hare numbers. Kit survival, which was 0% in 1986-87, peaked at 75% for kits of adult females and 26% for kits of yearlings in 1990-91. Emigration peaked annually from March-June, was lowest Sept.-Oct., and was not sex-biased. At least 16% (n= 22) of emigrants were trapped or shot. Seventeen lynx (14M, 3F) emigrated 100-1100 km. Annual natural mortality rates were under 11% for the first 6 years of study, including 2 years of hare decline, 60% in 1992-93 and 25% in 1993-94. The carcass sample contained 36% fewer kits, 40% more yearlings, and 4% fewer adults than were present on the study area, reflecting the lower birth and survival rates of kits of yearling females and trapping bias. Mean annual lynx home range size did not vary with hare density, until 1992-93 when male ranges increased markedly, and 1993-94 when female ranges increased. We recommend a network of permanently assigned untrapped areas to facilitate normal lynx population responses to changing snowshoe hare densities, to prevent local extinctions, and to maximize lynx harvests over a complete population cycle.

Grizzly Ursus arctos and black bear U. americanus densities in the interior mountains of North America

Abstract We collected hair samples from bears and used microsatellite genotyping to identify individual bears on three study areas near the Canadian Rocky Mountains. We estimated density of grizzly bears Ursus arctos in eight different ecosystems across five study areas, including the reanalysis of two previously published data sets. We also estimated black bear U. americanus density for two ecosystems in one study area. Grizzly bear density was lowest in boreal and sub-boreal plateau areas, moderate in the Rocky Mountain east slopes and highest in the Rocky Mountain west slopes. Presumably these gross differences are related to ecosystem productivity. In the Rocky Mountain west slopes, grizzly bear density was lower in populations that were partially isolated from the continuous bear population to the north. Presumably, these differences have more to do with human impacts on habitat and survival than ecosystem productivity, because productivity in partially isolated areas was similar to productivity in adjacent continuous populations. We show that large differences in bear density occur down to the ecoregion scale; broader ecosystem classes such as Bancis (1991) grizzly bear zones, ecoprovinces or ecozones would include areas with major differences in density and are therefore too coarse a scale at which to predict grizzly bear density. There appears to be little movement across ecoregion boundaries further suggesting that this may be an appropriate scale at which to extrapolate density. Differences in density across finer-scale ecosystems are likely due to seasonal movements and not population level differences in density. Average bear movements were longer in less productive ecosystems. Female grizzly bears did not appear to leave their home ranges to fish for salmon Oncorhynchus spp., and extra-territorial movements by males appeared to be rare, in both ecosystems which supported spawning salmon.

Lynx recruitment during a snowshoe hare population peak and decline in Southwest Yukon

We estimated litter size, birthrate (proportion of F with young in mid-Jun), and survival of young to winter for lynx (Lynx lynx) in southwest Yukon between 1990 and 1992. Radiocollared females were located shortly after parturition to count young, and relocated in winter to count the number of surviving young from tracks. Hare (Lepus americanus) density, as estimated by pellet transects, peaked at 7.4 hares/ha in 1990 and began to decline in winter 1990-91. Reproducing lynx faced a declining food supply in spring 1991. Litter size averaged 5.3 (n = 12) for adults (>2 yr) and 4.2 (n = 5) for yearlings in 1990, and all females monitored had litters in mid-June. Adult litter size was 4.9 in 1991 (n = 15) and 16 of 19 adult females (84%) had litters in mid-June. None of 7 yearlings retained litters in 1991. In 1992 none of 7 adult or 3 yearling females retained litters. Minimum survival estimated from track counts was 0.63 in 1990 and 0.75 in 1991 for kittens of adult mothers. Survival was 0.26 in 1990 for kittens of yearlings. Recruitment to 1 year of age was 2.8 kittens per adult female, and 0.55 kittens per yearling female in 1990. In 1991 recruitment was 3.2 from adults and 0.08 from yearlings. Lynx recruitment went from a peak in 1990 to zero reproductive output in 1992. Adult females managed to recruit young the year after the hare peak, but recruitment from yearlings virtually ceased in the first year of the hare decline. Recruitment from yearlings was surprisingly low, even in the peak hare year. If this observation describes other lynx populations, it has serious ramifications for trapped populations, which are often composed largely of yearlings. Population models which have based yearling recruitment on in utero data probably have overestimated recruitment and sustainable harvest.

Ecological investigations of grizzly bears in Canada using DNA from hair, 1995–2005: a review of methods and progress

Abstract Grizzly bears (Ursus arctos) occur across British Columbia and in Alberta in mostly forested, mountainous, and boreal ecosystems. These dense forests make sighting bears from aircraft uncommon and aerial census impractical. Since 1995, we have used genetic sampling using DNA from bear hair collected with barbed wire hair traps to explore a suite of ecological questions of grizzly bears in western Canada. During 1995–2005, we conducted large-scale sampling (1,650 to 9,866 km2 grids) in 26 areas (covering a combined 110,405 km2), where genetic identification of 1,412 grizzly bears was recorded. Abundance estimation was the primary goal of most surveys. We also used DNA from bear hair to examine population trend, distribution, and presence in areas where grizzly bears were rare, as well as population fragmentation in a region with a high human population. Combining spatial variation in detecting bears with that of human, landscape, and ecological features has allowed us to quantify factors that influence grizzly bear distribution, population fragmentation, and competition with black bears (U. americanus), and to map variation in bear densities. We summarize these studies and discuss lessons learned that are relevant to improving sampling efficiency, study designs, and resulting inference.

Using placental scar counts to estimate litter size and pregnancy rate in Lynx

We compared post-partum estimates of litter size and pregnancy rate (Mowat et al. 1996) with those estimated from placental scar counts to test the accuracy of the placental scar method. We counted placental scars on uteri taken from lynx (Lynx lynx) carcasses collected from trappers over 3 years of a hare peak and decline in southwest Yukon. We classified scars into ≤ 6 categories based on coloration, though we lumped scars into subjective categories called light, medium and dark for analysis. In utero estimates of litter size were equally close to post-partum litter size when light placental scars were included or excluded. However, pregnancy rate was closest to live birthrate when all scars were included. We recommend researchers classify placental scars after Englund (1970) (or Lindstrom [1981]) with the addition of a seventh category for scars from previous years. We suggest researchers include all scars to estimate pregnancy rate and litter size, except those from previous years. This will increase precision and comparability among studies.

Estimating Mountain Goat Abundance using DNA from Fecal Pellets

ABSTRACT Non-invasive collection of tissue samples to obtain DNA for microsatellite genotyping required to estimate population size has been used for many wildlife species but rarely for ungulates. We estimated mountain goat (Oreamnos americanus) population size on a mountain complex in southwestern British Columbia by identification of individuals using DNA obtained from fecal pellet and hair samples collected during 3 sampling sessions. We identified 55 individuals from 170 samples that were successfully genotyped, and estimated a population of 77 mountain goats (SE = 7.4). Mean capture probability was 0.38 (SE = 0.037) per session. Our technique provides one of the first statistically rigorous estimates of abundance of an ungulate species using DNA derived primarily from fecal pellets. Our technique enables managers to obtain minimum counts or population estimates of ungulates in areas of low sightability that can be used for conservation and management.

Predicting grizzly bear density in western North America.

Conservation of grizzly bears (Ursus arctos) is often controversial and the disagreement often is focused on the estimates of density used to calculate allowable kill. Many recent estimates of grizzly bear density are now available but field-based estimates will never be available for more than a small portion of hunted populations. Current methods of predicting density in areas of management interest are subjective and untested. Objective methods have been proposed, but these statistical models are so dependent on results from individual study areas that the models do not generalize well. We built regression models to relate grizzly bear density to ultimate measures of ecosystem productivity and mortality for interior and coastal ecosystems in North America. We used 90 measures of grizzly bear density in interior ecosystems, of which 14 were currently known to be unoccupied by grizzly bears. In coastal areas, we used 17 measures of density including 2 unoccupied areas. Our best model for coastal areas included a negative relationship with tree cover and positive relationships with the proportion of salmon in the diet and topographic ruggedness, which was correlated with precipitation. Our best interior model included 3 variables that indexed terrestrial productivity, 1 describing vegetation cover, 2 indices of human use of the landscape and, an index of topographic ruggedness. We used our models to predict current population sizes across Canada and present these as alternatives to current population estimates. Our models predict fewer grizzly bears in British Columbia but more bears in Canada than in the latest status review. These predictions can be used to assess population status, set limits for total human-caused mortality, and for conservation planning, but because our predictions are static, they cannot be used to assess population trend.

Winter habitat associations of American martens Martes americana in interior wet-belt forests

Abstract I systematically sampled American marten Martes americana presence in two large study areas in the Selkirk and Purcell Mountains of southwest Canada using hair removal traps and tracks in snow. Both study areas were mostly forested and contained a broad cross-section of stand ages including abundant early seral and mature forest. I extracted measures of forest structure and dominant tree species, climax ecosystem types and human use from digital resource databases and used multiple logistic regression to model habitat selection of martens. I summarized data in windows of 100 m to 10 km in radius around each sample location to investigate the effect of varying data resolution on habitat selection. Marten detection at hair sites was positively related to temperature and trap duration and negatively related to snowfall while the trap was set. Martens were detected in all habitats sampled including recently logged areas, regenerating stands, dry Douglas-fir Pseudosuga menziesii forest and subalpine parkland. Overall selection was mildly greater using mean habitat values in 100 m and 2 km radius windows for both study areas. Martens selected for greater crown closure and older stands at the finer resolution; no selection for forest structure was detected at the larger resolution except that martens selected against increased overstory heterogeneity as measured by the standard deviation of crown closure (within the window). Martens preferred coniferous stands over deciduous dominated stands and were more abundant in wetter than in dryer ecosystems. Selection for ecosystems and stand types was stronger in the larger window size. At the intensity sampled in this study, neither road density nor logging appeared to affect marten habitat selection when I accounted for variation in ecosystems and stand structure. This study examined habitat selection at relatively coarse scales; stronger associations with forest structure may be expected at finer scales. In addition, roads or logging may influence habitat selection below the scale of my analysis.