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Perspectives on the design and execution of DNA-based inventories for bears using hair sampling

Perspectives on the design and execution of DNA-based inventories for bears using hair sampling

I review 3 decades of experience involving DNA-based sampling for bear (Ursus spp.) inventories and provide some considerations for future users. Some of the less obvious suggestions follow. (1) Do not set baited sites in closed forest; rather, put them in places where wind can move the smell of the bait to a nearby bear. (2) More females and cubs will be detected if you sample later in the year, which will likely improve the accuracy and precision of density or population estimates. (3) Plot a histogram of movement distances to confirm that there are no outliers in the data, which could bias the estimate of range size and generate underestimates of density. (4) Use spatial capture–recapture methods to analyze your data. Spatial methods allow for clustered sampling designs that require less field effort and allow empirical extrapolation to areas that were not sampled, which can inform management decisions at the scale decisions are made. (5) Consider the spatial covariates before the fieldwork to ensure field sampling captures the range of spatial variation in these variables. (6) DNA-based sampling can be a particularly efficient way to monitor population trend because passive rub sites are largely permanent and can be used year after year; rub sites can be established by the user; sampling rub sites can be done with volunteers to reduce field costs; and the sampling intensity for a long-term inventory can be modest and still yield useful inference.