Test of a Critical Density Index Assumption: A Case Study with Gray Partridge

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Abstract
Gray partridge (Perdix perdix) call counts and density estimates were obtained simultaneously to evaluate a population index. We obtained calling data from 3,288 4-minute listening station surveys and density estimates from 1,115 km of line transect sampling during 1983-85. The number of calling groups during morning surveys in summer 1983, spring 1984, summer 1984, and spring 1985 was positively correlated (r=0.955, P=0.023) with population density. Number of calling groups during morning surveys and density both declined (P < 0.05) from summer 1983 to spring 1984 and from summer 1984 to spring 1985. Neither changed (P > 0.05) from spring 1984 to summer 1984. Our data indicate that it is appropriate to utilize morning counts of calling groups during spring or summer as an index to gray partridge density. Calling frequency during summer evenings was not directly related to population density, demonstrating the danger of using an untested index. This may be the 1st avian study to test the commonly assumed relationship between an index and density.

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