Line-transect sampling for estimating ptarmigan (Lagopus spp) density

Current methods of estimating ptarmigan density require total counts, and hardly apply to areas exceeding 1 km(2). We evaluated the applicability, accuracy, and efficiency of line-transect sampling as an alternative method for estimating breeding density of male ptarmigan. We compared Hayne's and generalized Hayne's estimators with line transect estimators based on perpendicular distance. We surveyed 6 subalpine areas in Kluane, Yukon, with 231 km of transects in 1995 and 1996, in addition to a 77-ha grid where we also conducted total counts. Estimates of perpendicular distance were accurate (bias = -3 to -7%). Their efficiency resides mainly in detecting changes in density over 2-year periods in highly or moderately fluctuating populations. Performance of Hayne's estimator was close to that of perpendicular distance (coefficient of correlation, r = 0.95), even if in many cases the average sighting angle was not 32.7 degrees. The generalized Hayne's estimator was not robust; biases were up to -90%. The results of this survey, with densities ranging between 0 and 65 males/km(2) for similar and adjoining subalpine areas, dispute the principle that the ''health'' of a population can be assessed by censusing only a small area.