Brood-count Power Estimates of Rio Grande Turkey Production in Texas

Wildlife Outstanding Technical Paper

Brood counts are used frequently by state conservation agencies to estimate wild turkey (Meleagris gallopavo) recruitment. We performed power analyses for 25 years of Rio Grande Wild Turkey (M. g. intermedia; RGWT) brood-count data from five ecological regions of Texas in order to determine if these data had sufficient (1-b ?0.80) power to detect inter-annual and long-term changes in turkey production of 10%-20%, which we considered biologically meaningful. We then analyzed the data to determine trends in production. The analyses showed that a minimum annual sample of 200-500 turkey-group observations per region was required to detect an inter-annual change of 10%-20% in the proportion of poults in the hen:poult population. Historic annual sample size averaged 65-306. Existing data were not sufficiently powerful to detect long-term changes of 10%-20% in poult proportions. Brood counts, as currently conducted, appear to be ineffective at detecting biologically meaningful changes in RGWT recruitment in Texas. Further, non-random sampling methodology may render data unreliable. We recommend reevaluation of TPWD's efforts to monitor RGWT populations, as well as investigations into the sensitivity of RGWT populations to changes in recruitment. Our results show that power analysis offers a powerful tool for designing and evaluating population monitoring schemes.

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