干旱区生态环境知识资源中心

We evaluated the strengths, weaknesses, relative effort, and cost of four survey techniques for indexing black-tailed jackrabbit (Lepus californicus) and desert cottontail (Sylvilagus audubonii) abundance in arid scrub habitats in the San Joaquin Valley of California in April 2004. The four survey techniques were aerial, spotlight, track station, and visual encounters along foot transects. Rabbit abundance indices in areas with and without shrubs were 5.79/km and 0.04/km for aerial surveys, 0.5/km and 2.94/km for spotlight surveys, 1.53/ km and 0.27/km for visual encounter surveys, and 52% and 40% visitation rates for track station surveys. Visual encounter, spotlight, and aerial surveys all provided species-specific counts of individuals that can be used to estimate an index of abundance (e.g., number/km) or density using distance methods. Track stations provided a visitation rate but the number of individuals and species could not always be determined. Visual encounter and aerial surveys measured diurnal habitat use, spotlight surveys measured nocturnal habitat use, and track stations measured both. For visual encounter and spotlight surveys, rabbit observability was reduced in areas with shrubs compared to areas without shrubs resulting in a habitat bias. Road availability can limit access for visual encounter, spotlight, and track station survey’s but not aerial surveys. For two biologists working two 8-hour days, estimated number of sampling units and costs (labor, materials, travel) for each technique were 24 track stations ($27.05/ station), 40 km of visual encounter transects ($16.36/km), 140 km of aerial transects ($16.00/km), and 100 km of spotlight transects ($6.80/km). Project objectives, study site attributes, and budgets will determine which survey technique might yield the best results and be most cost-effective for a given project.