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

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Abstract
Line transect sampling was used to estimate density of P. perdix on a 160 km2 study area in eastern South Dakota [USA] using newly developed estimation techniques. Transects (272) were made during surveys in fall, mid-winter and early spring 1979-1980. Density estimates were 48 birds/km2 (SE = 10.3) in late fall, 21/km2 (SE = 5.0) in mid-winter and 29/km2 (SF = 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. This technique is more reliable than an index of abundance based on numbers observed per unit of distance traveled for appearing population fluctuations. Assuming a closed population and based on fall and mid-winter density estimates, early winter mortality was 56% (SE = 14). The data indicate that estimates of gray partridge mortality based on reduction in average covey size can be severely biased by covey mixing.

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