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.

Woody cover, when expressed at the scale of the 207 km 2 Cusenbary Draw basin, remained unchanged (~23%) from 1955 to 1990. When expressed at the scale of range sites, woody cover declined on sites with relatively high production potential and increased on sites with relatively low production potential. Change in woody cover distribution at sub-range site scales, increased low and high woody covers and decreased intermediate woody cover, would be expected to lead to increased water yield at the basin scale because there was an apparent threshold woody cover (~20%) above which simulated evapotranspiration (ET) changed little with increasing woody cover. This potential increase, however, was more than offset by the decreased water yield due to increased ET loss associated with compositional changes of woody vegetation from oak to juniper. A set of woody cover-ET regression curves was developed for different range sites based on simulation studies using the SPUR-91 hydrologic model. Based on these woody cover-ET regression curves and GIS analysis, no brush management would result in a 35% decrease in water yield, while a hypothetical brush management cost-share program would increase water yield by 43% over the 1990 level. Benefits in water yield and forage production from brush management differ in different range sites. A brush management cost-share program that preferentially allocated brush management to sites with deep soil and the highest forage production potential increased water yield by 50%, compared to a 100% increase if brush management were preferentially allocated on sites with shallow soil and highest water yield potential. These model results illustrate that the spatial scale of assessment and spatial distribution of brush management among range sites should be important concerns associated with developing and evaluating brush management policies.

Distance sampling during aerial surveys has been used extensively to estimate the density of many wildlife species. However, practical issues arise when using distance sampling during aerial surveys, such as obtaining accurate perpendicular distances. We assembled a computerized, electronic system to collect distance‐sampling data (e.g., transect length, detection location, and perpendicular distance) during aerial surveys. We tested the accuracy of the system in a controlled trial and a mock survey. We also evaluated the electronic system during field surveys of northern bobwhite (Colinus virginianus) conducted in the Rio Grande Plains and Rolling Plains ecoregions of Texas, USA, during December 2007–2008. For comparison, we evaluated the accuracy of visual estimation of distance during a mock survey. A strong linear relationship existed between estimated and actual distances for the controlled trial (r2 = 0.99) and mock survey (r2 = 0.98) using the electronic system. Perpendicular‐distance error (i.e., absolute difference between estimated distance and actual distance) for the electronic system was low during the controlled trial (1.4 ± 0.4 m; ${\bar {x}}$ ± SE) and mock survey (3.0 ± 0.5 m) but not during the visual estimation of distance (10 ± 1.5 m). Estimates of bobwhite density obtained using the electronic system exhibited reasonable precision for each ecoregion during both years (CV < 20%). Perpendicular‐distance error slightly increased with target distance (0.7‐m increase in error for every 10‐m increase in target distance). Overall, the electronic system appears to be a promising technique to estimate density of northern bobwhite and possibly other terrestrial species for which aerial‐based distance sampling is appropriate. © The Wildlife Society, 2012

Quail hunting consists of a complex set of behaviors that involve humans, pointing dogs, and wild birds. The recent development of models known as Hunter-Covey Interface (HCI) theory provides an opportunity to analyze how we perceive, understand, and manage quail hunting. There are 2 groups of HCI models: static and dynamic. The static HCI model predicts daily hunting mortality based on the velocity of the hunt and area covered during a hunt. The dynamic HCI models estimate the probability of flushing a covey given a set of circumstances that revolve around the potential rate of which quail learn to avoid hunters. We quantified the variables required to test whether the static and dynamic models of HCI theory provide meaningful results. We used spatial data on hunting velocity and area covered during >100 quail hunts, along with estimates of quail population density, mortality, and movements from 2 areas in south Texas, to evaluate output from HCI models. The static model predicted average daily harvest rates that ranged from 5 to 50 birds. This average is within the range of average daily bag of south Texas quail hunters in groups of 2-4. Output from the dynamic models suggested that quail populations on our study areas were subjected to relatively low hunting intensities with a corresponding low avoidance behavior and learning rate, which is a scenario that matched 1 of 4 predictions by Guthery (2002). We found it difficult to meet basic assumptions of HCI theory. For example, hunting pressure was potentially redundant, coveys were not always randomly distributed in space, and the extent to which quail are naive at the beginning of a hunting season was unknown. However, both the static and dynamic HCI models appeared robust to violation of these assumptions. Application of HCI theory may provide meaningful results that can be used to manage quail hunting pressure, optimize harvest, and sustain populations. JOURNAL OF WILDLIFE MANAGEMENT 69(2):498-514; 2005

Ground-penetrating radar (GPR) is an innovative and non-invasive method that uses radar to penetrate the ground and develop three-dimensional digital images of the top several meters of the earth. Ground-penetrating radar has been used extensively in the fields of engineering, military science, forensic science, archaeology, and environmental remediation, but has received little attention by wildlife professionals. We demonstrated a possible application of GPR for wildlife studies for mapping burrow systems using maritime pocket gophers (Geomys personatus maritimus), a subspecies of concern as listed by the U.S. Fish and Wildlife Service. Ground-penetrating radar surveys were conducted at Naval Air Station-Corpus Christi on five 15-m  15-m areas with >200 above-ground gopher mounds/ha during July 2007. Survey areas were scanned with a Geophysical Survey Systems Inc. SIR-3000, GPR digital control unit and a 900-MHz ground-coupled antenna. Within the 5 areas, we located 8 gophers and mapped 267 m of tunnels that had an average depth of 0.6 m. We were able to differentiate deteriorating or abandoned tunnels from active tunnels, detect an underground pipeline, and distinguish changes in soil texture using GPR. Ground-penetrating radar is a non-destructive and non-invasive method to gain knowledge of fossorial animal movements and potential destabilization of soil integrity. Ó 2013 The Wildlife Society.

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