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Accuracy of home-range estimates in animals is influenced by a variety of factors, such as method of analysis and number of locations, but animal space use is less often considered and frequently over-generalized through simulations. Our objective was to assess effect of an ad hoc (h_ad hoc) smoothing parameter in kernel analysis from two species that were predicted to have different patterns of utilization distributions across a range of sample sizes. We evaluated variation in home-range estimates with location data collected from GPS collars on two species: mule deer Odocoileus hemionus and coyotes Canis latrans. We calculated home ranges using 95% and 50% kernel contours using reference (h_ref and h ad hoc smoothing parameters. To evaluate the influence of sample size, we calculated home ranges using both smoothing parameters for random subsamples of 5, 10, 25 and 50% of GPS locations and compared area estimates to estimates for 100% of GPS locations. On mule deer, we also conducted visual relocations using conventional radiotelemetry, which resulted in fewer locations than GPS collars. Area was overestimated at smaller sample sizes, but an interesting pattern was noted with higher relative bias at 60–100 locations than at sample sizes < 50 locations. Relative bias was most likely due to increased smoothing of outer data points. Subsampling allowed us to examine relative bias across a range of samples sizes for the two smoothing parameters. Minimum number of points to obtain a consistent home range estimates varied by smoothing method, species, study duration, and volume contour (95% or 50%). While h_ad hoc performed consistently better over most sample sizes, there may not be a universal recommendation for all studies and species. Behavioral traits resulting in concentrated or disparate space use complicates comparisons among and between species. We suggest researchers examine their point distribution, justify their choice of smoothing parameter, and report their choices for home-range analysis based on their study objectives.
The current reestablishment and growth of beaver Castor fiber populations throughout Eurasia has created a need for methods to control population size. While lethal-trapping has been the most common harvest and control method for beaver world-wide for centuries, in recent decades spring hunting has developed as the main lethal method in Norway, Sweden and Finland. An experimental hunt where hunters annually removed 22–26% (mean = 24%) of the estimated spring population of beavers on 242 km2 in southeast Norway led to an unanticipated 46% decline in colony number after only three years. We monitored the population response in colony number throughout the ensuing four years of no hunting during which time the number of colonies rebounded by 93%. The rapid increase in colony number suggested a high rate of dispersal to vacated colony sites by animals from unexploited colonies within the study area (approximately half were unexploited each year) and from bordering townships where harvest was light at the time. Increased fecundity usually follows in the wake of a significant reduction in the density of mammal populations and most likely contributed to the rapid rebound in colony number observed. We conclude that spring hunting can be employed to significantly reduce population size when desired and that over-exploited populations may rebound quickly after hunting stops when dispersing individuals are in adequate supply from colonies both within and outside the harvested area.
Traditional methods for estimating white-tailed deer population size and density are affected by behavioral biases, poor detection in densely forested areas, and invalid techniques for estimating effective trapping area. We evaluated a noninvasive method of capture—recapture for white-tailed deer Odocoileus virginianus density estimation using DNA extracted from fecal pellets as an individual marker and for gender determination, coupled with a spatial detection function to estimate density (spatially explicit capture—recapture, SECR). We collected pellet groups from 11 to 22 January 2010 at randomly selected sites within a 1-km2 area located on Arnold Air Force Base in Coffee and Franklin counties, Tennessee. We searched 703 10-m radius plots and collected 352 pellet-group samples from 197 plots over five two-day sampling intervals. Using only the freshest pellets we recorded 140 captures of 33 different animals (15M:18F). Male and female densities were 1.9 (SE = 0.8) and 3.8 (SE = 1.3) deer km-2, or a total density of 5.8 deer km-2 (14.9 deer mile-2). Population size was 20.8 (SE = 7.6) over a 360-ha area, and sex ratio was 1.0 M: 2.0 F (SE = 0.71). We found DNA sampling from pellet groups improved deer abundance, density and sex ratio estimates in contiguous landscapes which could be used to track responses to harvest or other management actions.
The estimation of large carnivore populations presents major logistical challenges. We examined trends in the wolf Canis lupus population in Finland using two independent methods. We compared track indices from an annual wildlife winter census based on a constant, nationwide network of transect lines (wildlife triangles) with the number of reproductions confirmed to occur in the same year during 1996 to 2009. Nationwide, and in the eastern management zone, which is the core area of Finnish wolves, the frequency of wolf tracks in wildlife triangles (% of all triangles counted in a given year having wolf tracks) predicted quite well the log transformed number of reproductions taken place in these areas (adjusted R2-values for linear regression models 0.59 and 0.68, respectively), while not for the western management zone (R2 = 0.38). However, although mean wolf densities were low (< 1 wolf/1000 km2 nationwide and <3 wolves/1000 km2 in the eastern zone), track indices could detect the major trends in Finland's wolf population. A clear reason for this was the substantial changes in population size during the study period.
Hunters' preferences for different harvest principles and harvest regulations such as season length and harvest quotas provide important knowledge for wildlife management. We report results from a survey of 2788 willow ptarmigan hunters regarding commonly used harvest-principles and -regulations. A harvest quota strategy was the most preferred principle. Hunters were in general more positive to an annual bag, than daily quotas. Age was a particularly strong predictor of the ‘no winter hunt’ (after 23 December) regulation, and also a fairly strong predictor for the per annum and per day quota strategies respectively. This study has shown that ptarmigan hunters prefer annual quotas, rather than shortened hunting season or reduced number of hunters. We also emphasize the importance of social—ecological systems thinking when adaptive management strategies are developed and that management strategy evaluation models should be used to evaluate these strategies.
It is often challenging to use invasive methods of individual animal identification for population estimation, demographic analyses, and other ecological and behavioral analyses focused on individual-level processes. Recent improvements in camera traps make it possible to collect many photographic samples yet most investigators either leap from photographic sampling to assignment of individual identity without considering identification errors, or else to avoid those errors they develop computerized methods that produce accurate data with the unintended cost of excluding participation by local citizens. To assess human ability to visually identify Andean bears Tremarctos ornatus from their pelage markings we used surveys and experimental testing of 381 observers viewing photographs of 70 Andean bears of known identity. Neither observer experience nor confidence predicted their initial success rate at identifying individuals. However, after gaining experience observers were able to achieve an average success at identifying adult bears of 73.2%, and brief simple training further improved the ability of observers such that 24.8% of them achieved 100% success. Interestingly, observers who were initially more likely to falsely identify two photos of the same bear as two different bears than vice versa were likely to continue making errors and their bias became stronger, not weaker. Such biases would lead to inaccurate population estimates, invalid assessments of the bears involved in conflict situations, and underestimates of bear movements. We thus illustrate that in some systems accurate data on individual identity can be generated without the use of computerized algorithms, allowing for community engagement and citizen science. In addition, we show that when using observers to collect data on animal identity it is important to consider not only the overall frequency of observer error, but also observer biases and error types, which are rarely reported in field studies.
The Cantabrian brown bear Ursus arctos population can be seen as a paradigm in conservation biology due to its endangerment status and genetic uniqueness. Therefore, the need to obtain basic demographic data to inform management actions for conservation is imperative. Despite this, empirical data on the size and trends of the Cantabrian bear population are scarce. Here we present the first estimates of population size (Nc) and effective population size (Ne) of the whole Cantabrian brown bear population. We genotyped 270 non-invasive samples collected during 2006 throughout the entire range of the population and subsequently identified 130 individuals. Different model estimators of Nc based on capture—markrecapture (CMR) procedures were compared. The average for the best three models (Mh Chao, Mh Darroch and CAPWIRE TIRM) yielded a total estimate of Nc = 223 individuals (CI95% = 183–278) and Ne 50 (CI95% = 36–75) providing an Ne / Nc ratio of 0.22. Estimates for the two subpopulations commonly recognized in the Cantabrian range were Nc = 203 (CI95% = 168–260) and Ne = 47 (CI95% = 36–70) for the western subpopulation and Nc = 19 (CI95% = 12–40) and Ne= 9 (CI95% = 8–12) for the eastern subpopulation. These data suggest that the Cantabrian brown bear population has increased recently, mainly in the western subpopulation, after a long period of decline and isolation which lead to the split of the population at the beginning of the 20th century. Population sizes in the early 1990s were thought to be only 60 individuals for the western subpopulation and 14 individuals in the eastern one. The efforts to improve conservation policies made since then have probably contributed, to some extent, to the population increase during the last couple of decades.
Oil and gas development is widespread in west—central Alberta, yet little is known about the potential impacts of oil and gas activities on grizzly bear habitat use. Focusing on the impacts of one component of energy development, we studied the selection patterns of radio-collared grizzly bears in relation to oil and gas wellsites in the Kakwa region of west—central Alberta. For each grizzly bear foraging season (spring, summer, and fall), we calculated a population level resource selection function (RSF) to assess the probability that bears would select for wellsites versus non-wellsite habitat. We used mixed-effects logistic regression and model selection to examine factors that could influence the probability of wellsite use, including: grizzly bear reproductive status, wellsite age, wellsite operational status, surrounding road and wellsite densities, adjacent forest canopy cover, and adjacent habitat. Bear reproductive status, surrounding road and wellsite densities, and adjacent canopy cover had the most influence on the probability of wellsite use. Females used wellsites more than expected in all seasons, and males selected for wellsites in summer and fall. Males used wellsites less than females, and females with young used wellsites more than both single females and males. Bears were more likely to use wellsites that had lower densities of disturbance (roads and wellsites) in the surrounding area. In the fall, older wellsites were also more likely to be used by bears. In areas with human access, grizzly bears attracted to anthropogenic features are at a higher risk of human-caused mortality; therefore, their use of wellsites could have negative results for this threatened population.