An evaluation of population indices for northern bobwhite

Abstract

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.

Optimizing detection of the bobwhite reproduction call using passive acoustic monitoring

“…Covey counts using human observers generally assume a detection radius of approximately 500 m (DeMaso et al 1992, Wellendorf and Palmer 2005). Commonly applied radii of detection for whistle counts with human observers vary from 400–800 m (Stoddard 1931, Rollins et al 2005, Terhune et al 2009, Reyna et al 2012, Kubečka et al 2019). For the covey call, others detected 31.5% of manually detected calls through automated detection in Kaleidoscope, with the farthest detection being 241 m (Wilhite et al 2020).…”

Using drones equipped with thermal cameras to locate and count quail individuals and coveys: A case study using Northern Bobwhite Colinus virginianus in Mississippi, USA

“…Weather variables, such as wind speed and changes in barometric pressure, have also been shown to affect covey calling frequency and probability of detection (Seiler et al, 2002;Wellendorf et al, 2004). As such, many researchers have questioned the reliability of these indices, as they often lead to challenges in obtaining accurate or precise population counts (Kubečka et al, 2019;Rusk et al, 2007Rusk et al, , 2009. Alternate methods for improving capture and estimating accurate population sizes of bobwhite could be useful (Elmore et al, 2023;Martin, 2020).…”