Line transect estimates of mountain quail density

We estimated the density of 4 populations of mountain quail (Oreortyx pictus) in northern California during the breeding season (May-Jun) 1983. Estimates of density (D) were obtained from Fourier series analyses of perpendicular distance data. D values ranged from 9 to 30 quail/100 ha, with associated coefficients of variation (CV) <20%. Percent relative density values calculated from the estimates of D compared favorably with percent relative number of quail detected/km of transect. In general, mountain quail were behaviorally compatible with line transect sampling. J. WILDL. MANAGE. 50(3):373-377 The reclusive nature of the mountain quail has made it difficult for managers to estimate the population densities of this common game bird. Previous estimates of mountain quail density were based on strip censuses and summarized in abstracts of Pittman-Robertson projects more than 30 years ago (E. V. Miller, unpubl. reps., Calif. Dep. Fish and Game, Sacramento, 1950, 1951). Miller (1950:136) stated that the density estimates from his research were of "doubtful accuracy" and furthermore claimed that "accurate censusing of mountain quail is often impossible" (Miller 1951:9). Miller was unable to obtain accurate estimates of mountain quail density because the strip census method relies on the strict assumption that all objects of interest within the strip(s) will be detected. This assumption is almost assuredly violated when a secretive species such as the mountain quail is censused. If objects are missed during a strip census, then the resulting density estimate must be adjusted for this bias. The information needed to adjust for bias that results from objects not being detected during a strip census is not always available, however. Because the strip census technique is a special type of line transect sampling (Burnham and Anderson 1984, Burnham et al. 1985) it is possible to circumvent the problem of being unable to obtain a complete count within a given area by collecting perpendicular distance measures from each detected object to the transect line. The perpendicular distance data then are used to derive a probability density function and hence density for a given population (cf. Burnham et al. [1980], Buckland [1985]). Thus, the use of an appropriate line transect density estimator allows a manager to estimate the density of a biological population from a sample count rather than a complete census. The objectives of this paper are to: (1) demns rate that mountain quail population densities can be estimated during the breeding season with the line transect methods developed by Burnham et al. (1980), (2) compare the estimates of density with relative measures of abundance, and (3) examine the extent to which our estimates of mountain quail density meet the major assumptions of line transect density estimators. R. J. Gutibrrez reviewed earlier drafts of this paper and provided many helpful suggestions. Th s tudy benefitted greatly from discussions with B. R. Noon. J. Brown and D. Spain drew the figures. Financial support was provided in part by the Int. Quail Found. and the Calif. Dep. For. -For. Resour. Assessment Program. Computer resources were provided by the Humboldt State Univ. Comput. Cent.