Productivity Estimates From Upland Bird Harvests: Estimating Variance and Necessary Sample Sizes

Abstract: Harvest of upland game birds in concert with sampling of age ratios from wings can yield important biological information about populations. Although estimates of productivity are commonly produced, they are often not accompanied by a measure of variance. Thus, we developed standard error estimates for sample productivity ratios, compared 4 methods for creating confidence intervals for population productivity ratios, and developed a test and the corresponding sample size requirements for comparing 2 population productivity ratios. We applied these techniques to greater sage-grouse (Centrocercus urophasianus) wing-data collected in Oregon, USA (1993–2005). Computer simulations indicated that backtransforming the Wilson's score interval on the proportion of immatures in the sample results in the most reliable confidence intervals among the methods considered. We recommend to managers measuring conservation action outcomes with productivity ratios to consider the appropriate sample sizes for the spatial and temporal scale of their monitoring programs.