An evaluation of population indices for northern bobwhite.

Northern bobwhite (Colinus virginianus) populations are monitored using 2 general approaches—population indices and abundance estimators. Due to their convenient sampling designs, indices are commonly used by land managers and researchers to predict or estimate hunting‐season populations. We evaluated the efficacy of 4 bobwhite indices (spring cock [adult male] call‐counts, autumn covey call‐counts, roadside surveys, and helicopter surveys) to predict hunting‐season population size by relating them to abundance estimators (minimum known population [no. unique trapped individuals each year], mark–recapture, helicopter‐based distance sampling). Data were collected at the Rolling Plains Quail Research Ranch in Fisher County, Texas, USA, during 2009–2018. Spring cock call‐counts and autumn covey call‐counts were analyzed at 2 spatial scales: ranch scale (1,781 ha) and point scale (i.e., within the presumed radius of audibility of listening points; 600 m or 113 ha). Roadside and helicopter surveys were conducted at the ranch scale along 31‐ and 90‐km transects, respectively. At the ranch scale, mean spring cock call‐counts were a modest predictor of minimum known populations (r2 = 0.54) and good predictor of mark–recapture estimates (r2 = 0.80). At the point scale, the mean number of cocks heard was a poor predictor of densities surrounding points (r2 = 0.0003) as estimated by distance sampling. The mean number of coveys heard during autumn counts was a significant predictor of both minimum known populations (r2 = 0.88) and mark–recapture estimates (r2 = 0.85) at the ranch scale but was a weak predictor of densities immediately surrounding listening points (r2 = 0.22). Helicopter surveys during November (individuals/km) were a significant predictor of minimum known populations (r2 = 0.98) and mark–recapture (r2 = 0.93). Overall, roadside surveys (individuals/km) conducted during September was the best index for predicting minimum known populations (r2 = 0.99) and mark–recapture estimates (r2 = 0.97). Our results suggest the linear relationship between indices and autumn–winter populations for bobwhite are stronger when conducted closer in time to hunting season and at larger scales. © 2019 The Wildlife Society. This study was conducted to evaluate linear relationships between commonly adopted indices and abundance estimators for northern bobwhite (Colinus virginianus) in the Rolling Plains of Texas, USA, for practitioners seeking to predict or estimate autumn hunting populations. We found that indices conducted at larger scales and closer in time to hunting season may be considered more reliable for predicting abundance. [ABSTRACT FROM AUTHOR]