Long-Term Population Analysis of Gray Partridge in Eastern Washington

Abstract

Recent studies reported that gray partridge (Perdix perdix) populations have declined throughout Europe and Asia. Gray partridge on the Palouse Prairie of Washington also have been reported to be in decline. Therefore, we analyzed densities of gray partridge on the Palouse Prairie of Washington to determine long-term population trends (1940-92). We also tested for density dependence in recruitment and fall-and-winter mortality rates and attempted to relate annual variation in recruitment and mortality to weather and habitat variables. Spring and/or fall estimates of density were available for 33 of 53 years and varied from 1.3 to 23.2 birds/km 2 in the spring and from 0.1 to 28.6 birds/km 2 in the fall. The population's return point from 1940 to 1954 was 3.45 birds/km 2 versus 6.72 birds/km 2 from 1982 to 1992, indicating that density was higher in the more recent period. Surprisingly, this result contrasts with a series of reports that indicated that the population was in serious decline. We detected density-dependent effects on recruitment rate, fall-and-winter mortality rate, and annual change in population size. Density dependence had the strongest effects on recruitment rate. Recruitment rate averaged 1.55 (SE = 0.27) but ranged widely (0.38-3.38). Fall-and-winter mortality averaged 0.29 (SE = 0.06). We were not able to explain variation in population-growth rate or fall-and-winter mortality rate using habitat and/or weather variables (P > 0.11). Under current habitat conditions, density typically will be 6.7 birds/km 2 in the spring and 10.4 birds/km 2 in the fall and can be expected to vary markedly independent of density. By combining available datasets, we developed a lengthy time series adequate for investigating long-term population dynamics. Such an approach may be possible and informative for other populations.