Line Transect Estimates of Density and the Winter Mortality of Gray Partridge

Line transect sampling was used to estimate density of gray partridge (Perdix perdix) on a 160- km2 study area in eastern South Dakota using newly developed estimation techniques. We traversed 272 transects during surveys in fall, mid-winter, and early spring 1979-80. Density estimates were 48 birds/km2 (SE = 10.3) in late fall, 21/km2 (SE = 5.0) in mid-winter, and 29/km2 (SE = 5.9) in early spring, but only fall to mid-winter estimates were different (P < 0.05). Partridge were behaviorally compatible with the assumptions of line transect sampling. We illustrate that this technique is more reliable than an index of abundance based on numbers observed per unit of distance traveled for appraising population fluctuations. Assuming a closed population and based on fall and mid-winter density estimates, early winter mortality was 56% (SE = 14). Our data indicate that estimates of gray partridge mortality based on reduction in