An Evaluation of Survey Methods for Estimating Northern Bobwhite Abundance in Southern Texas

Abstract

Distance sampling has been identified as a reliable and well‐suited method for estimating northern bobwhite (Colinus virginianus) density. However, distance sampling using walked transects requires intense sampling to obtain precise estimates, thus making the technique impractical for large acreages. Researchers have addressed this limitation by either resorting to the use of indices (e.g., morning covey‐call surveys) or incorporating the use of aerial surveys with distance sampling. Both approaches remain relatively untested. Our objectives were to 1) compare density estimates among morning covey‐call surveys, helicopter transects, and walked transects; 2) test a critical assumption of distance sampling pertinent to helicopter surveys (i.e., all objects on line are detected); and 3) evaluate the underlying premise of morning covey‐call surveys (i.e., that the no. of calling coveys correlates with bobwhite density). Our study was conducted on 3 study sites in Brooks County, Texas, USA, during October to December, 2001 to 2005. Comparisons between walked transects and morning covey‐call surveys involved the entire 5‐year data set, whereas helicopter transects involved only the latter 2 years. Density estimates obtained from helicopter transects were similar to walked transect estimates for both years. We documented a detection probability on the helicopter transect line of 70 ± 10.2% (% ± SE; n = 20 coveys). Morning covey‐call surveys yielded similar density estimates to walked transect estimates during only 2 of 5 years, when walked transect estimates were the least accurate and precise. We detected a positive relationship (R2 = 0.51; 95% CI for slope: 29.5–53.1; n = 63 observations) between covey density and number of coveys heard calling. We conclude that helicopter transects appear to be a viable alternative to walked transects for estimating density of bobwhites. Morning covey‐call surveys appear to be a poor method to estimate absolute abundance and to depict general population trajectories.

Computer-automated bird detection and counts in high-resolution aerial images: a review

“…Waterbirds, including waterfowl, seabirds, shorebirds, and wading birds, are the most frequent subjects of aerial surveys (Chabot and Bird ), although upland game birds (Rusk et al. , Butler et al. ) and raptors (Good et al.…”

Efficiency of Fixed-Width Transect and Line-Transect-based Distance Sampling to Survey Red Junglefowl (Gallus gallus spadiceus) in Peninsular Malaysia

“…The scope of ecology covers distribution of organism and its abundance (Buckland, 1993;2001). And estimating the abundance has been a challenge in wildlife science because many previous surveys used indices to estimate relative abundance (Rusk, 2007). The managers and biologists have to consider the most cost-effective way to survey a population and later come out with very reliable estimates in order to apply them in the management.…”

An electronic system to collect distance‐sampling data during helicopter surveys of northern bobwhite

“…Other more efficient modes of traversing transects, such as aircraft, have been used as a possible solution. Aircraft have been used to survey for a wide variety of wildlife including white‐tailed deer ( Odocoileus virginianus ; DeYoung 1985), mule deer ( Odocoileus hemionus ; White et al 1989), elk ( Cervus elaphus ; Noyes et al 2000), northern bobwhite ( Colinus virginianus ; Shupe et al 1987, Rusk et al 2007), and waterfowl (Cordts et al 2002). However, data‐collection issues can arise when using aerial modes of transportation and distance sampling.…”

“…However, data‐collection issues can arise when using aerial modes of transportation and distance sampling. These issues include maintaining a predetermined centerline and obtaining accurate perpendicular distances and survey‐line length (Shupe et al 1987, Buckland et al 2001, Marques et al 2006, Rusk et al 2007).…”