Assessing indirect measures of abundance and distribution with remote cameras: Simplifying indices of activity at pygmy rabbit burrows

Estimating abundance or distribution of species that are scarce or difficult to detect is challenging for wildlife biologists. Pygmy rabbits (Brachylagus idahoensis) are secretive, sagebrush (Artemisia spp.) obligates of conservation concern that occupy the Intermountain West, USA. These unique leporids are difficult to monitor; however using remote cameras in conjunction with ranking of burrow activity may help refine sampling techniques for these mammals. We classified and deployed remote cameras at 405 burrows of pygmy rabbits between 2006 and 2010 in six study areas across Utah, USA. We ranked burrows based on the appearance of fecal pellets, as well as the condition of burrow entrances. We also documented the presence of pygmy rabbits and potential competitors and predators of pygmy rabbits at burrows using remote cameras. We used mixed-effects, zero-inflated negative binomial models and AIC model selection to evaluate the relative influences of burrow activity ranking, season, and rate of photographs for potential competitors and predators of pygmy rabbits on photo rates of pygmy rabbits. The top 2 models supported a simplified (active or inactive) burrow classification system and accounted for 45% of AIC weight. Rates of pygmy rabbit photographs were further influenced by meters from habitat edge (β=0.0008±0.0004, 95% CI=7.07E-05–0.002), photo rate of cottontail rabbits (β=0.31±0.11, 95% CI=0.08–0.53), and were higher during summer than other times of the year (β=0.38±0.19, 95% CI=0.01–0.74). Mean number of days to detection of pygmy rabbits at burrow complexes classified as active was four (SE=0.61), and a two-week sampling period was needed to capture 81% of first detections. Our results refine commonly used ranking criteria of burrow complexes to a 2-level scale (active and inactive), and also emphasize the use of remote cameras as an effective technique for quantifying activity of pygmy rabbits at burrow complexes. Such information can help researchers and land managers more effectively survey this species for conservation and management efforts.