IDENTIFYING PREDATORS AT NORTHERN BOBWHITE NESTS

Abstract: We identified nest predators of northern bobwhites (Colinus virginianus) on private lands in northern Florida and southern Georgia, USA, using continuous infrared micro-video cameras, 1999–2001, and compared these results to predictions based on diagnostic sign at nests. Mammals (59%), snakes (29%), and ants (12%) accounted for known bobwhite nest depredations. Mammalian predators, in order of importance, were the raccoon (Procyon lotor), nine-banded armadillo (Dasypus novemcinctus), Virginia opossum (Didelphis virginiana), bobcat (Lynx rufus), hispid cotton rat (Sigmodon hispidus), and coyote (Canis latrans). Using diagnostic sign, technicians correctly classified 30% of mammalian depredations to species and overestimated nest depredations by snakes. A classification tree model correctly classified 75% of the test sample (n = 33) into “mammal” or “snake” categories, but still overestimated depredations by snakes. We documented a broader predator community upon bobwhite eggs than previously known for northern Florida and southern Georgia and confirmed that snakes were significant nest predators in some years. We conclude that diagnostic sign at depredated nests was unreliable for identifying nest predators of northern bobwhites.     

Nest success of northern bobwhite on managed and unmanaged landscapes in southeast Iowa

Range-wide declines in northern bobwhite populations (Colinus virginianus) have been attributed to concomitant loss of breeding habitat. Bobwhite management efforts to restore this habitat resource can be informed by empirical studies of associations between breeding success and multi-scale habitat attributes. We compared bobwhite nest success in 2 southern Iowa landscapes as a function of microhabitat and landscape composition. Lake Sugema Fish and Wildlife Area (LSWA) was managed to promote bobwhite recruitment, and Harrisburg Township (HT) was an adjacent landscape dominated by private agricultural production. Survival rate modeling based on telemetry data provided evidence for age-specific daily nest survival rate. Daily survival rates decreased as nest age increased, but the decline was more severe at HT. Nest survival at LSWA (S = 0.495, SE = 0.103) was nearly twice that on HT (S = 0.277, SE = 0.072). We found no evidence that habitat composition or spatial attributes within 210 m of a nest site significantly influenced nest success. Forb canopy at the nest site had a positive influence on nest success at HT but not at LSWA. We suggest nesting habitat with greater forb canopy cover will increase the opportunity for nesting success in landscapes with limited nesting habitat. © 2010 The Wildlife Society.     

Economics of Northern Bobwhite and Timber Management in the Southeastern United States

ABSTRACT Populations of northern bobwhite (Colinus virginianus) have declined significantly over the past 50 years, and the primary factor contributing to this decline has been the loss of habitat. Forest landowners who are concerned with providing bobwhite habitat as well as generating revenue from timber should balance the silvicultural requirements of timber production with the biological needs of the bobwhite. The goal of this study was to determine the economic tradeoffs between bobwhite and timber management and how to minimize loss or maximize profit when managing for bobwhite and timber simultaneously. I performed discounted cash flow analyses, calculated land expectation value, and determined the financially optimal rotation age and optimal timing and intensity of thinnings for loblolly pine (Pinus taeda) plantations under specific management objectives. My results show that the annual per-hectare economic gains of managing for both bobwhite and timber ranged from US$19.27 to $41.37 on site index 50 land, and ranged from $32.63 to $50.02 on site index 90 land. My analysis indicates that bobwhite management provides an investment opportunity to landowners whose low-productivity sites would be unprofitable if timber is the only product. My study provides an example of integrating multiple uses of goods and services in a way that maximizes economic returns and aids land managers in producing better habitat for bobwhite.     

Population Irruptions of Northern Bobwhite: Testing an Age-Specific Reproduction Hypothesis

Abstract: Age-specific reproduction has been suggested for northern bobwhite (Colinus virginianus) and has been hypothesized as a factor contributing to population irruptions. However, little research has been conducted on the subject. We conducted a laboratory and field study to determine if age-specific reproduction occurred in northern bobwhites. Our objectives were to compare 7 reproductive measures (% F nesting, date of first incubated nest, egg-laying rate, nesting rate, clutch size, egg mass, and egg hatchability) between first- and second-year breeders and determine if differential reproduction was impacted by diet quality. The laboratory study consisted of a 2 × 2 factorial experiment with age and diet quality (low protein [12%] and high protein [24%]) as the factors. Data for the field study represented a 6-year data set of bobwhite reproduction (May-Sep 2000-2005) obtained from an ongoing radiotelemetry study in southern Texas, USA. We documented similar productivity (i.e., % F laying, egg-laying rate, and egg mass) and timing of laying (i.e., date of first egg) between juvenile (n = 33) and adult bobwhites (n = 27) in our laboratory study. However, females on the high-protein diet exhibited a greater egg-laying rate than females on the low-protein diet. Under field conditions, we also documented no difference in productivity (% F nesting, nesting rate, clutch size, egg hatchability) and timing of nesting (date of first incubated nest) between age classes (n = 59 juv and 32 ad). Our findings do not support early suppositions of age-specific reproduction in quail. Quail irruptions should not be influenced by population age structure as it relates to age-specific reproduction.     

MICROCLIMATE VERSUS PREDATION RISK IN ROOST AND COVERT SELECTION BY BOBWHITES

Abstract: Knowledge of factors that influence habitat selection by wildlife leads to better understanding of habitat ecology and management. Therefore, we compared microclimate and predation risk as factors influencing the selection of stopping points (mid-day coverts, nocturnal roosts) by northern bobwhites (Colinus virginianus). Stopping points were located using radiomarked bobwhites in the Texas Panhandle, USA, during 2002–2003. We obtained blackbody temperatures of microclimates and assessed predation risk (angles of obstruction for aerial predators, vegetation profiles for terrestrial predators) at stopping points and paired random points. Summer coverts showed fewer degree-minutes of hyperthermic exposure (blackbody temperatures >39°C; x̄ = 655.0, SE = 4.1 for coverts, x̄ = 2,255.5, SE = 4.9 for random; 1200–1600 hr) and a lower risk to predators (e.g., 95% confidence intervals [CIs] of angles of obstruction = 87.8–90.8° for coverts, 55.9–70.6° for random). Summer roost temperatures were similar to paired random sites (x̄ = −13.9°C, SE = 0.6 for roost, x̄ = 13.9°C, SE = 0.7 for random) as were winter roost temperatures (x̄ = −1.3°C, SE = 0.7 for roosts, x̄ = −1.4°C, SE = 0.8 for random). There were minor issues of habitat selection of winter or summer roosts based on predation risk (e.g., 95% CIs of vegetation profiles of summer roosts and random sites did not overlap at lower strata). We concluded other selection factors likely exist for winter roosts because microclimate and predation risk assessments between winter roosts and random sites showed no difference. Similarly, other selection factors may exist for summer roosts, as they showed only a weak difference in terrestrial predation risk and no difference in microclimate in comparison to random sites. We concluded microclimate was the primary selection factor for coverts because prevention of hyperthermia necessitated that bobwhites select cooler microclimates within the study area.     

Effects of nestboxes on the breeding biology of Southern House Wrens Troglodytes aedon bonariae in the southern temperate zone

Nestboxes are known to increase clutch size, enhance breeding success and affect the social mating system of several cavity nesters. Although in recent years various cavity nesters have been studied in nestboxes in South America, the effects of boxes on the biology of the study species are unknown. We evaluated the effects of nestboxes on the breeding biology and social mating system of Southern House Wrens Troglodytes aedon bonariae by comparing birds breeding in nestboxes and tree cavities in two cattle ranches in Buenos Aires Province, Argentina. Southern House Wrens nesting in boxes had higher breeding success but, contrary to studies on the temperate zone, we did not find differences in clutch size between Wrens breeding in nestboxes and tree cavities. The main causes of nest failure in tree cavities were nest predation and flooding of the cavity (70 and 23% of the failures, respectively) while in nestboxes predation and desertion were the most important causes of failure (38 and 34% of the failures, respectively). The social mating system of Southern House Wrens is monogamy with biparental care, and neither was affected by the boxes. Males did not attract secondary females to additional nestboxes; however, nestboxes are safer breeding sites than tree cavities, and females seemed to prefer males with nestboxes on their territory. These results suggest that nest quality alone might be not enough for secondary females to accept polygyny.     

Identifying Predators and Nest Fates of Bobwhites in Southern Texas

Abstract: Predation is the primary cause of nest failure for northern bobwhites (Colinus virginianus). There are few reliable data documenting the species diversity and relative importance of bobwhite nest predators in southern Texas, USA. We used infrared video-monitoring systems to document nest fates of 127 bobwhite nests over 4 nesting seasons from 2002 to 2005 in southern Texas. A majority of depredation events (83%) were caused by 4 species: coyote (Canis latrans), striped skunk (Mephitis mephitis), southern fire ant (Solenopsis xyloni), and badger (Taxidea taxus). Observed bobwhite nest fates for the study period were 0.50 successful, 0.34 depredated, and 0.16 abandoned or undetermined. A universal approach to mitigating nest predation is not likely to be applicable in regions similar to southern Texas, with high nest-predator diversity (e.g., fire ants, rodents, and mammalian carnivores). We believe that infrared video surveillance is a valuable tool for documenting baseline information on predator context and nest fate for many avian species, considering the limitations of past methods (e.g., postfate evidence).     

An improved multi-scale approach to modeling habitat occupancy of northern bobwhite

Predicting species presence requires knowledge of detection of individuals, scale of model variables, model selection uncertainty, and spatial autocorrelation. Our objective was to incorporate recent modeling advances to predict potential habitat occupancy of northern bobwhite (Colinus virginianus). From 15 May–15 August 2008 and 2009, we conducted repeat-visit surveys at 360 sites within Delaware to sample presence of bobwhite. We randomly selected half the data to model scale-dependent relationships of bobwhite presence with metrics of landscape- and site-scale habitat composition and configuration. The final averaged habitat-occupancy model fit the remainder testing dataset with an area under the receiver operating characteristic curve value of 0.62. At the site scale, bobwhite presence was negatively related to interspersion and juxtaposition of early successional habitat (ESH; grassland and shrubland), ESH to forest edge density, and agriculture to forest edge density, though relative effect sizes were weak to moderate after accounting for model selection uncertainty. At the landscape scale, bobwhite presence was negatively related to patch cohesion of human development within 2.5 km and positively related to patch cohesion of ESH within 2.0 km, with both variables exerting strong effects. Bobwhite presence was also weakly and positively related to percentage of shrubland habitat within 1.0 km of the sampling point. We applied our habitat occupancy model to map the predicted presence of breeding bobwhite within the Delmarva Peninsula, USA. The modeling results and distribution map will provide guidance to State and Federal private land management programs in the Mid-Atlantic to identify where habitat management efforts will be most effective. Our methodology can also serve as a basis for future habitat modeling of bobwhite and other grassland–shrubland species across their range. © 2011 The Wildlife Society.     

Effects of Tissue Collection Methods on Morphometrics and Survival of Captive Neonatal Northern Bobwhite

ABSTRACT We assessed effects of tissue collection methods (i.e., patagial microbiopsy and down feathers) and chick age at sampling on morphometrics and 21-day survival of 600 captive neonatal northern bobwhite (Colinus virginianus). We observed minimal effects on morphometrics and no difference in survival among patagial microbiopsy (x̄ = 0.96 ± 0.03), down feathers (x̄ = 0.92 ± 0.04), and control (x̄ = 0.86 ± 0.05) methods. DNA analysis from patagial microbiopsy, down feather, and egg tooth samples showed greater concentrations of DNA from patagial microbiopsy (x̄ = 10.28 ± 1.74 μg/ml) than either down feather (x̄ = 4.10 ± 1.74 μg/ml) or egg teeth (x̄ = 2.35 ± 1.74 μg/ml).     

Northern Bobwhites and Postfire Succession

ABSTRACT Our study evaluated the effects of prescribed fire on northern bobwhites (Colinus virginianus) occupying native rangelands in Rolling Plains of Texas, USA, during 2002 and 2003. Prescribed fires were conducted during February of 1996, 1998, and 2000; pastures with no recent treatment history served as controls. We quantified bobwhite densities from line transects using distance sampling. We used a repeated-measures analysis of variance to test for treatment-year differences in bobwhite densities. We measured postfire herbaceous and woody vegetation attributes and evaluated vegetation relationships to bobwhite density using simple linear regression. We found significant between-year differences in fall bobwhite densities (F = 13.05, df = 3, P = 0.036) but no differences among treatments or controls. Fall bobwhite densities were inversely related to visual obstruction (r² = 0.179, df = 15, P = 0.058) and positively associated with increasing heterogeneity of grass cover (r² = 0.416, df = 15, P = 0.004). Our results suggest prescribed fire at large spatial scales may be a neutral practice for managing bobwhite habitat on semiarid rangelands.     

Simulating density-dependent relationships in south Texas northern bobwhite populations

Density dependence influences northern bobwhite (Colinus virginianus) reproduction and overwinter mortality. However, the functional forms of these density-dependent relationships or the factors that influence them during the annual life cycle events of this bird are not clear. We used a systems analysis approach with a compartment model based on difference equations (Δt = 3 months) for bobwhites in South Texas to simulate population behavior using 16 different functional forms of density-dependent production and overwinter mortality. During the reproductive season, a weak linear density-dependent relationship resulted in the longest population persistence (up to 100.0 yr), whereas a reverse-sigmoid density-dependent relationship had the worst population persistence (2.5–3.5 yr). Regarding overwinter mortality, a sigmoid or weak linear density-dependent relationship and a weak linear or no density-dependent reproduction relationship had the longest population persistence (87.5–100.0 yr). Weak linear density-dependent reproduction with either sigmoid or weak linear overwinter mortality produced stable fall population trends. Our results indicated that density dependence may have a greater influence on overwinter survival of bobwhites than previously thought. Inclusion of density-dependent functional relationships that represent both density-dependent reproduction and overwinter mortality, were critical for our simulation model to function properly. Therefore, integrating density-dependent relationships for both reproductive and overwinter periods of the annual cycle of bobwhite life history events is essential for conducting realistic bobwhite population simulation analyses that can be used to test different management scenarios in an integrated and interdisciplinary manner. © 2012 The Wildlife Society.     

Estimates of Survival from Radiotelemetry: a Response to Guthery and Lusk

Abstract: Radiotelemetry has become an important and frequently used tool in wildlife research. Inferences drawn from radiotelemetry data depend on the assumption that the radiotransmitters are not influencing parameter(s) of interest. An article by Guthery and Lusk (2004) in the Wildlife Society Bulletin questioned the validity of this assumption for estimating survival rates of northern bobwhites (Colinus virginianus) using radiotelemetry data. In this evaluation, we address technical and philosophical flaws in Guthery and Lusk's (2004) critique of northern bobwhite studies utilizing radiotelemetry. They concluded that biologists should be skeptical of radiotelemetry studies and they advised researchers to design studies to address potential biases caused by radiotransmitters using independent data. Although we agree that researchers are responsible for testing key assumptions of their techniques, we believe Guthery and Lusk's (2004) conclusions were not well supported and were based on tenuous assumptions. Guthery and Lusk (2004) calculated the level of productivity (given as a fall age ratio) required to balance a simple population model that contained published estimates of annual survival and assumed an annual finite population growth rate of 1.0. We review their population model and show that the relationship between an annual survival rate and fall age ratio is nonlinear. This nonlinearity can lead to biased estimates of a fall age ratio, especially at lower values of annual survival. We also question the validity of using fall age ratios as an estimator of productivity. Further, we suggest that this assessment of a radiotransmitter effect from a survival rate itself is not appropriate. This rate can be depressed (or elevated) for a variety of reasons not related to the influence of radiotransmitters. In addition, Guthery and Lusk (2004) assumed that daily survival rates (as calculated from both annual and seasonal published estimates) were constant throughout the year; thus, they scaled daily survival rates from seasonal to annual estimates. Further, their meta-analysis was hindered by temporal pseudoreplication and a lack of independence among the observations used in the analysis. We conclude the weight of the evidence presented by Guthery and Lusk (2004) is not as strong as they claim because it fails to meet the test of sufficient causation. While scientists should always be skeptical and critical of assumptions of all methods employed in wildlife research, more rigorous tests are necessary before we discredit a valuable technique without sufficient empirical evidence.     

Habitat-Suitability Bounds for Nesting Cover of Northern Bobwhites on Semiarid Rangelands

ABSTRACT Northern bobwhite (Colinus virginianus) is a species for which extensive knowledge exists regarding its ecology, life history, and habitat. Although the qualitative aspects of bobwhite habitat have been described and known for many decades, researchers have neglected to characterize bobwhite habitat quantitatively (i.e., habitat selection). Thus, biologists have been capable of identifying components that compose bobwhite habitat but have only been able to speculate on how much of each component was necessary. We documented selection-avoidance behavior of nesting bobwhites in Brooks County, Texas, USA, during May-August, 2004–2005. We measured 5 vegetation features (i.e., nesting-substrate ht and width, suitable nest clump density, herbaceous canopy coverage, and radius of complete visual obstruction) at nest sites (n = 105) and at random points (n = 204). We used continuous selection functions to assess habitat use and identify bounds of suitability. Selection domains for nesting-substrate height and radius of complete visual obstruction were 16.9–31.2 cm and 1.05-4.35 m, respectively. Across all measurements, bobwhites selected for nest sites with a nesting-substrate width ≥22.4 cm, suitable nest-clump density ≥730 nest clumps/ha, and herbaceous canopy coverage ≥36.7%. This knowledge will provide an important foundation for managers to evaluate current nesting conditions on semiarid rangelands and provide a basis for habitat management aimed at creating suitable nesting habitat for bobwhites.     

Behavior of Walk-Hunters and Pointing Dogs During Northern Bobwhite Hunts

Abstract: Data on the behavior of walk-hunters and pointing dogs aids in understanding and managing quail harvest. We collected Global Positioning System track logs and recorded behaviors of hunters and dogs on northern bobwhite (Colinus virginianus) hunts in Oklahoma (n = 43), Texas (n = 43), and Missouri (n = 7), USA, during the 2005–2006 and 2006–2007 hunting seasons. Hunter velocity averaged 0.8 ± 0.03 (SE) m/second both seasons (n = 85) and pooled (95% CL overlap) velocity of bird dogs was 2.5 ± 0.07 (SE) m/second (n = 154). Hunters spent 60.5 ± 2.4% (SE) of their time walking in 2005–2006 (n = 45) versus 75.2 ± 3.5% (SE) in 2006–2007 (n = 48); respective figures for ranging by dogs were 50.2 ± 2.2% (n = 57) versus 82.0 ± 1.3% (SE; n = 97). Mean duration of a hunt declined from 82.3 ± 8.16 (SE) minutes (n = 45) to 50.2 ± 5.1 (SE) minutes (n = 48) between seasons. Variation in bobwhite abundance was the primary cause of seasonal variation in hunter and dog behaviors because covey-associated activities declined as quail abundance declined. With our results and those of previous workers, managers have first-generation estimates of all variables in hunter-covey interface models for managing bobwhite harvest on discrete areas.     

Impacts of weather on northern bobwhite sex ratios,body mass,and annual production in South Texas

A landscape-scale assessment of how bobwhite productivity varies in relation to weather does not exist for northern bobwhite (Colinus virginianus). We collected age and sex ratio and body mass data from hunter-harvested bobwhites in 16 counties of South Texas (n = 72,797 bobwhites) during 2001–2009 hunting seasons. We evaluated annual bobwhite production (juvenile:adult age ratios) as a function of cumulative April–August rainfall using National Oceanic and Atmospheric Administration (NOAA) weather station data from Falfurrias and Hebbronville, Texas. We observed minimal among-year change in percent males harvested (51.0–54.5% male) and mean mass (156–160 g) of bobwhites across South Texas. We found no relationship between percent male or body mass and weather. We documented a positive, linear relationship between cumulative April–August rainfall and bobwhite age ratios (r² = 0.94); we also documented a negative, linear relationship between summer (Jun–Aug) mean maximum daily temperature and bobwhite age ratios (r² = 0.38). Our results suggest that rainfall is a landscape-scale indicator of annual bobwhite production in South Texas and can thus be used to manage annual expectations of quail hunters prior to the hunting season. © The Wildlife Society, 2012     

Estimating Duration of Short-Term Acute Effects of Capture Handling and Radiomarking

ABSTRACT Radiotelemetry is used extensively in zoographic studies of wildlife species, including northern bobwhite (Colinus virginianus). These studies assume that radiomarking does not affect survival of marked individuals. However, most researchers implicitly acknowledge that capture, handling, and radiomarking may have short-term deleterious effects on individuals and, therefore, include in analyses only animals that survive an adjustment period of arbitrary length (often 7 days) following capture and marking. Length of adjustment period is rarely empirically based and may potentially bias survival estimates. We outline an analytical approach to determine an appropriate adjustment period and illustrate this approach by examining effects of time-since-marking on survival of 410 northern bobwhite captured during winter from 1997 to 2001, in Mississippi, USA. We modeled daily survival rates using time-since-marking as a covariate in the nest-survival model of Program MARK. Although survival varied among and within years, we found no evidence to suggest that standard adjustment periods of 7–14 days were appropriate for our sample. If adjustment periods are used in radiotelemetry studies, those that are empirically based may be more appropriate than arbitrarily set periods.     

A population model to simulate northern bobwhite population dynamics in southern Texas

Models are important tools that can help managers and researchers understand the population dynamics of a species and how different habitat or population management scenarios impact that species. We used radio-telemetry data from northern bobwhites (Colinus virginianus) in southern Texas from 2000 to 2005 to develop a stochastic simulation model for bobwhite populations. Our model is based on difference equations, with stochastic variables drawn from normal and Weibull distributions. We simulated bobwhite populations to 100 yr and evaluated our model by comparing results with independent estimates of 4 population parameters (spring and fall density, finite rate of increase in the fall population [λ], and winter juv:ad age ratios). Using a quasi-extinction criterion of ≤40 birds (density = ≤0.05 birds/ha), probability of persistence to 100 yr was 88.3% (106 of 120 simulations) for the spring population and 96.7% (116 of 120 simulations) for the fall population. Using a less restrictive quasi-extinction criteria (≤14 birds), probability of persistence was 93.3% (112 of 120 simulations) for the spring population and 98.3% (118 of 120 simulations) for the fall population. Simulated population parameters were similar to independent estimates for 4 of 4 population parameters. Winter age ratios differed between our model ( juv:ad, n = 120, SE = 0.32) and empirical age ratios from harvested bobwhites on our study area ( juv:ad, n = 25, SE = 0.24). However, when we corrected harvest age ratios for bias in juvenile harvest ( juv:ad, n = 25, SE = 0.32) simulated and empirical estimates were similar. Our model appears to be a reliable predictor of bobwhite populations in the southern Texas. Our simulation results indicate that bobwhite hunters and managers can expect excellent bobwhite hunting (fall populations ≥2.2 birds per ha) in about one of 10 yr. © 2011 The Wildlife Society