Effect of Radiotransmitters on Northern Bobwhite Annual Survival

Abstract: Radiotelemetry has been widely used in northern bobwhite (Colinus virginianus) research to estimate survival rates and other demographic parameters. Biologists have used this knowledge to study bobwhite ecology, develop management theory, and base management actions. We tested the assumption that radiotransmitters do not bias survival rates of bobwhites by comparing survival rates of banded bobwhites with and without radiotransmitters on Tall Timbers Research Station (TTRS) from 1999 to 2004. We used Burnham's model in Program MARK and model-selection procedures to determine relative importance of year, gender, and radiotagged status on annual survival rates and recovery processes. Three plausible models (relative quasi-likelihood Akaike's Information Criterion [ΔQAIC_c] < 3) included year dependence in survival and an additive effect of gender but no radiotransmitter effect. Models including a radiotransmitter effect in survival were >8 ΔQAIC_c from the top models, had low Akaike model weights (w_i < 0.007), and low importance weight (S̀w_i(radio) = 0.01). We also compared band—recapture survival estimates from the QAIC_c minimizing model to staggered entry Kaplan—Meier (KM) survival estimates from 2000 to 2003. Annual KM survival estimates of male and female bobwhites were within the 95% confidence interval of band—recapture estimates in 7 of 8 comparisons. We conclude that radiotelemetry is a reliable technique for determining bobwhite survival. Managers should view information from properly conducted telemetry research as reliable and useful for management.     

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.     

Home range, movement, and site fidelity of translocated northern bobwhite (Colinus virginianus) in southwest Georgia, USA

During 1997 and 1998, we compared home range, movement, and site fidelity characteristics of translocated wild northern bobwhite (Colinus virginianus) to resident birds using radiotelemetry. We captured wild bobwhites (n=74) in southwest Georgia, USA just before the breeding season and relocated them (>1.6 km from capture sites) to sites nearby where previous density estimates revealed that populations were low compared to surrounding areas. Translocated birds were equipped with radiotransmitters and released in groups of 8 to 12. Resident birds (n=166) were also captured and simultaneously monitored via radiotelemetry. We found no difference in home range size (F ₁=0.08, P=0.78), mean daily movements (F ₁=0.04, P=0.84), or distance moved from trap or release sites to arithmetic centers of home ranges (F ₁=1.58, P=0.21) between translocated and resident bobwhites. These results suggest that translocating wild bobwhites over relatively short distances into suitable habitat does not negatively influence bobwhite movement and renders site fidelity as reasonable. Therefore, translocation of wild bobwhites before breeding season can result in enhanced numbers of adult breeders in a target location and potentially augments fall populations via reproductive yield.     

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     

Population Ecology of the Eastern Box Turtle in a Fragmented Landscape

Abstract: In the mid-Atlantic region, urban sprawl and development have resulted in habitat alterations and fragmentation; however, the effects on eastern box turtle (Terrapene carolina carolina) populations are unclear. To investigate the status of eastern box turtle populations in a fragmented landscape, we used mark—recapture and radiotelemetry to estimate population density, sex ratio, age structure, and survival on 4 study areas with differing degrees of isolation and human disturbance in northern New Castle County, Delaware, USA. We estimated adult population densities ranging from 0.81 turtles/ha to 3.62 turtles/ha among our 4 study areas. Sex ratios were male-biased at 2 study areas and balanced at 2 study areas. Proportion of juveniles ranged from 0% to 31%. Estimated annual survival rate ranged from 0.813 to 0.977. Mortality of radiotagged and marked turtles was primarily due to natural causes, but mowing was the primary cause of human-induced mortality. We found evidence of population decline at one study area due to low survival and recruitment. Human disturbances, isolation, and habitat composition appear to have the greatest influence on the box turtle populations we studied. To minimize mortality from human disturbance, we suggest planting crops adjacent to forest habitat that require no mowing or mowing at a height ≥15 cm. (JOURNAL OF WILDLIFE MANAGEMENT 72(3):745–753; 2008)     

Aspects of northern bobwhite ecology on south Florida US pastureland

During 2004 and 2005, we monitored breeding season survival, home range, habitat use, density, and reproduction of northern bobwhite (Colinus virginianus) in the peninsular region of Florida, USA. We radio-tagged 81 birds across a 20-km² cattle ranch consisting predominately of rotationally grazed pastureland. Birds were radio-tracked three to five times per week until mortality or the transition to nonbreeding season. We found no difference in home range size among the sexes, ages, or their interaction. Mean home range size pooled for years, sexes, and age class was 56.28 ha (±7.87 SE). Home ranges of bobwhites were not distributed among habitats randomly (second order: Λ?=?0.10; 7, 35 df; P?=?0.002). In addition, bobwhites did not use the habitats within their home range at random (third order: Λ?=?0.14, 5, 35 df; P?=?0.02). Estimated seasonal survival was 0.28 (±0.12 SE) and was best explained by the time-dependent model. Reproductive metrics indicated adequate reproduction and values consistent with the bobwhite literature. Bobwhite density (birds per hectare) in 2004 was 0.52 (±0.54 95 % confidence interval [CI]) and 0.75 (±0.51 95 % CI) for 2005. These results suggest that pastureland landscapes managed with rotational grazing can support bobwhite populations, albeit at low densities. More conservation attention should be directed towards improving these systems for bobwhite restoration.     

Quail and rain in semiarid rangelands: Does management matter?

Rainfall is a strong driver of quail populations on southwestern rangelands and can account for a large portion (~70–95%) of the variability in regional quail production and abundance. Landowners have attempted to moderate these boom-and-bust fluctuations via management; however, presently it is unknown whether management can increase or stabilize quail populations in semiarid environments or whether rainfall remains as influential at small spatial extents. Our objectives were to evaluate the efficacy of management at mitigating the effects of rainfall on northern bobwhite (Colinus virginianus) populations on semiarid rangelands and to quantify the influence of rainfall on bobwhite density at smaller spatial extents. We conducted a study to evaluate these objectives during 2014–2020 in the Rio Grande Plains (n = 11 sites; 1,100‒6,500 ha) and Rolling Plains (n = 4 sites; 1,900‒4,000 ha) of Texas, USA. We estimated bobwhite density during late autumn (Dec‒Jan) on all sites using helicopter surveys within a distance-sampling framework. We also obtained site-level seasonal rainfall (Apr‒Aug) and quantified management intensity via landowner surveys and a scoring rubric to categorize sites into 3 classes (low, medium, and high management intensity). Bobwhite populations during this study experienced a boom-bust cycle in both the Rio Grande Plains and Rolling Plains, with mean bobwhite density fluctuating considerably (0.57‒2.96 bobwhites/ha and 0.02‒2.88 bobwhites/ha, respectively). In the Rio Grande Plains, mean bobwhite density significantly increased from low to high management intensity in 2015 (1.12 ± 0.17 bobwhites/ha vs. 2.87 ± 0.39 bobwhites/ha, respectively), 2016 (1.06 ± 0.20 bobwhites/ha vs. 2.96 ± 0.36 bobwhites/ha, respectively), 2017 (0.73 ± 0.16 bobwhites/ha vs. 1.91 ± 0.32 bobwhites/ha, respectively), and 2019 (0.42 ± 0.14 bobwhites/ha vs. 1.01 ± 0.26 bobwhites/ha, respectively; P < 0.05). In addition, rainfall at the site level accounted for a low amount of the variation in bobwhite density (r² = 0.09; P < 0.01). Similarly, in the Rolling Plains, mean bobwhite density significantly increased from low to high management intensity in 2015 (1.30 ± 0.27 bobwhites/ha vs. 2.20 ± 0.29 bobwhites/ha, respectively) and 2016 (1.26 ± 0.26 bobwhites/ha vs. 2.88 ± 0.34 bobwhites/ha, respectively; P < 0.05). Rainfall at the site level also accounted for a low amount of the variation in bobwhite density (r² < 0.02; P = 0.82). Our findings suggest that management can increase bobwhite density beyond that of less-managed properties but does not completely eliminate inter-annual fluctuations in semiarid environments. In addition, rainfall appears to exert less of an influence on bobwhite density at a site level (e.g., 2,000 ha) than has been documented at a regional level (e.g., ≥8 million ha).     

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.     

Transmitter Effects on Growth and Survival of Forster's Tern Chicks

Radio-telemetry is a commonly used scientific technique that allows researchers to collect detailed movement, habitat use, and survival data of animals; however, evidence indicates that using telemetry can affect behavior and survival. Using multiple breeding colonies and years, we investigated the effects of attached radio-transmitters on growth and survival of Forster's tern (Sterna forsteri) chicks in San Francisco Bay, California, USA, 2010–2011. We tested these potential effects at isolated islands that allowed for high re-capture rates (typically >85%) in radio-marked and banded-only chicks. Modeled Gompertz growth curves suggested that transmitters had a small negative effect on some of the asymptotic growth parameters of tern chicks; tarsus (−1.5 ± 0.7% [SE]), culmen (−1.7 ± 1.2%), and wing (−4.9 ± 2.0%) lengths were shorter for radio-marked chicks compared to banded-only chicks. In contrast, there was no difference in asymptotic mass between radio-marked chicks and banded-only chicks. Survival from hatching to fledging was lower for radio-marked chicks than banded-only chicks during 2010 (banded-only = 0.313 ± 0.162 vs. radio-marked = 0.250 ± 0.165) and 2011 (0.193 ± 0.030 vs. 0.123 ± 0.027). Most of the transmitter effect occurred within the first week after hatching, rather than in older chicks. Notably, the effect of transmitters on chick survival was primarily additive, indicating that the effect of transmitters on radio-marked chicks was not influenced by other ecological covariates. Given the effect radio-transmitters had on survival did not change across temporal or ecological gradients, transmitters can still be used to evaluate ecological factors affecting survival and timing of mortality and radio-marked birds can be used to make inferences to the general population. Published 2020. This article is a U.S. Government work and is in the public domain in the USA.     

Effects of fire management on northern bobwhite brood ecology

Northern Bobwhite Colinus virginianus chicks require ample invertebrates for growth and feather development. Early successional or resprouting vegetation provides invertebrates for chicks but may not provide other resources such as roosting and loafing cover that is typically provided by later successional stages. Thus, management for bobwhites provides multiple seral stages in close proximity but the effects of landscape interspersion have not been tested for bobwhite broods. During a 2-year study, we explored the effects of landscape complementation and food availability on growth and survival of bobwhite chicks. We found growth of chicks to be negatively related to home range size which was negatively correlated to the amount of area burned. We also found survival of chicks to be positively related to the amount of burned area (i.e., foraging area) within brood home ranges. To maximize the growth and survival of bobwhite chicks, it would be necessary to increase access to foraging areas while decreasing the size of brood home ranges. Access to foraging areas can be created through frequent prescribed fire at small spatial scales.     

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.     

Management Implications of Cover Selection Data: Northern Bobwhite Example

Abstract: We derived a method of estimating the direction and magnitude of cover changes for potentially maximizing wildlife abundance on an area. We illustrate the method with data on cover selection by northern bobwhites (Colinus virginianus) collected in the Texas Panhandle from 2000 to 2003. We used radiotelemetry to determine use of cover associations, Geographic Information System analysis to determine their availability, and logic related to use-availability analysis to collapse 95% kernel home ranges to usable space. Bobwhites selected mixed-shrub cover consisting of sand plum (Prunus angustifolia) and fragrant sumac (Rhus aromatica), and they avoided or neutrally used 8 other cover associations. However, grass upland and sand sagebrush (Artemisia filifolia) associations occurred in ≥86% of home ranges (n = 96 bobwhites with ≥30 radiolocations). Usable space averaged 54.2% ± 1.72 SE of kernel home ranges. The data indicated that adding about 226 ha of mixed-shrub cover or a structural homologue while simultaneously reducing the quantity of most other cover associations would maximize bobwhite abundance. An area with 30–60% mixed-shrub cover, with the balance in grass upland and sand sagebrush, and with cover dispersed such that no point was >30 m from mixed-shrub cover was hypothetically optimal for bobwhites in our region. Within certain constraints (e.g., financial, social, edaphic), managers can apply this method by manipulating cover types through relevant management practices (e.g., planting, prescribed burning, mechanical removal of vegetation). This method, with minor modification, could also be used to decrease usable space on an area, and thus decrease wildlife densities, should that be the manager's objective.     

Evaluation of three methods to estimate density and detectability from roadside point counts

Roadside point counts are often used to estimate trends of bird populations. The use of aural counts of birds without adjustment for detection probability, however, can lead to incorrect population trend estimates. We compared precision of estimates of density and detectability of whistling northern bobwhites (Colinus virginianus) using distance sampling, independent double-observer, and removal methods from roadside surveys. Two observers independently recorded each whistling bird heard, distance from the observer, and time of first detection at 362 call-count stops in Ohio. We examined models that included covariates for year and observer effects for each method and distance from observer effects for the double-observer and removal methods using Akaike's Information Criterion (AIC). The best model of detectability from distance sampling included observer and year effects. The best models from the removal and double-observer techniques included observer and distance effects. All 3 methods provided precise estimates of detection probability (CV = 2.4–4.4%) with a range of detectability of 0.44–0.95 for a 6-min survey. Density estimates from double-observer surveys had the lowest coefficient of variation (2005 = 3.2%, 2006 = 1.7%), but the removal method also provided precise estimates of density (2005 CV = 3.4%, 2006 CV = 4.8%), and density estimates from distance sampling were less precise (2005 CV = 9.6%, 2006 CV = 7.9%). Assumptions of distance sampling were violated in our study because probability of detecting bobwhites near the observer was <1 or the roadside survey points were not randomly distributed with respect to the birds. Distances also were not consistently recorded by individual members of observer pairs. Although double-observer surveys provided more precise estimates, we recommend using the removal method to estimate detectability and abundance of bobwhites. The removal method provided precise estimates of density and detection probability and requires half the personnel time as double-observer surveys. Furthermore, the likelihood of meeting model assumptions is higher for the removal survey than with independent double-observers. © 2011 The Wildlife Society.     

Demographic Sensitivity of Population Change in Northern Bobwhite

Abstract: The northern bobwhite (Colinus virginianus) is an economically important gamebird that is currently undergoing widespread population declines. Despite considerable research on the population ecology of bobwhites, there have been few attempts to model population dynamics of bobwhites to determine the contributions of different demographic parameters to variance of the finite rate of population change (Λ). We conducted a literature review and compiled 405 estimates of 9 demographic parameters from 49 field studies of bobwhites. To identify demographic parameters that might be important for management, we used life-stage simulation analyses (LSA) to examine sensitivity of Λ to simulated variation in 9 demographic parameters for female bobwhites. In a baseline LSA based on uniform distributions bounded by the range of estimates for each demographic parameter, bobwhite populations were predicted to decline (Λ = 0.56) and winter survival of adults made the greatest contribution to variance of Λ (r² = 0.453), followed by summer survival of adults (r² = 0.163), and survival of chicks (r² = 0.120). Population change was not sensitive to total clutch laid, nest survival, egg hatchability, or 3 parameters associated with the number of nesting attempts (r²<0.06). Our conclusions were robust to alternative simulation scenarios, and parameter rankings changed only if we adjusted the lower bounds of winter survival upwards. Bobwhite populations were not viable with survival rates reported from most field studies. Survival rates may be depressed below sustainable levels by environmental conditions or possibly by impacts of capture and telemetry methods. Overall, our simulation results indicate that management practices that improve seasonal survival rates will have the greatest potential benefit for recovery of declining populations of bobwhites.     

Influence of Radiotransmitters on Fecal Glucocorticoid Levels of Free-Ranging Male American Kestrels

ABSTRACT Although radiotelemetry is considered a valuable technique for ornithological field studies, several assumptions have been made about the impact that transmitters may have on the estimation of behavioral, ecological, and reproductive parameters. To assess the potential effects of backpack radiotransmitters, we captured and assigned 8 male American kestrels (Falco sparverius) into 2 groups: radiotagged (n = 6) and control individuals (leg-banded, n = 2). Thereafter, we collected feces approximately 2 hours after capture (day −1), and subsequently during days 0 (releasing day), 4, 7, 15, 30, 40, and 55. Prior to fecal analysis, we validated the corticosterone enzyme immunoassay using standard procedures (e.g., parallelism, dose-response curve), and we confirmed physiological significance of fecal glucocorticoid metabolites through adrenocorticotropin challenge, which induced an increase of 4-fold (446.10 ± 60.73 ng/g) above baseline (114.27 ± 15.23 ng/g) within 4 hours (P < 0.001). Both groups exhibited a significant increase in fecal glucocorticoids during day 0 (P < 0.001), but concentrations returned to preattachment values within 4 days. Fecal glucocorticoid concentrations did not differ between samples of radiotagged and leg-banded kestrels (P > 0.05). In spite of the small number of monitored subjects, these findings suggested that radiotransmitters did not affect adrenocortical activity in these male American kestrels.     

Effect of Tooth Removal on Recaptures of Raccoons

Abstract: Researchers have extensively used mark—recapture techniques to obtain information on demographic parameters of wildlife populations. However, researchers have recognized that a number of factors can influence capture probabilities of wildlife species, which in turn can bias mark—recapture estimates of demographic parameters. Tooth extraction, which is a commonly used technique in studies of mesopredator species to obtain precise age estimates and to monitor the use of vaccine baits, is an aspect of animal handling that clearly might affect the recapture probability of individuals. However, the effect that tooth removal has on the individual recapture probabilities of wildlife species is unknown. During 2005, we trapped and marked 91 raccoons (Procyon lotor) in northern Indiana, USA, as part of a mark—recapture study designed specifically to determine if tooth extractions have an effect on recapture probabilities of individuals. We performed tooth extractions on 50% of the raccoons at the time of capture, and we attempted to balance tooth extractions with respect to sex and age of raccoons. We used logistic regression to model the effects of sex, age, and tooth removal on recapture probabilities, and we used Mann—Whitney U-tests to examine the effect of tooth removal on the number of times we recaptured individuals. The probability of recapture differed between sexes but did not differ as a function of tooth removal or among age classes. In addition, we failed to detect any difference in the mean number of times that we recaptured raccoons between the tooth removed and non—tooth-removed groups. Our results suggest that managers can use tooth extractions as an effective management tool without biasing population estimates or compromising other management objectives.     

Northern Bobwhite Chick Survival and Effects of Weather

Reliable vital rates for all life stages are necessary to identify limiting factors in wildlife populations and inform sound wildlife management. The difficulty associated with capturing and tagging precocial young, such as northern bobwhite chicks (Colinus virginianus), and linking variation in recruitment to ecological conditions has contributed to significant knowledge gaps in their population ecology. During 1999–2017, we captured and patagial-tagged ≤12-day-old bobwhite chicks (n = 3,576) and estimated their survival from time of capture (Jun–Sep) to fall and winter (Nov and Jan) recapture and winter (Feb) recovery. We used Burnham's model implemented in Program MARK to integrate mark-recapture and dead-recovery (via harvest) data to estimate survival for the 19-year study. By including weather covariates, we also evaluated explicit hypotheses related to temperature and precipitation effects on chick survival. We found inter-annual, intra-annual, and intra-seasonal variation in chick survival with an average annual daily survival estimate of 0.9887 (95% CI = 0.9321, 0.9918). Precipitation amount and number of precipitation (>0.635 cm) events during the first 4 weeks post-tagging decreased the daily survival rate of chicks curvilinearly. Average minimum daily temperature and maximum daily temperature effects on survival were negligible, but an interaction between minimum temperature and cumulative precipitation during the first 14 days post-tagging affected survival. We recommend population modelers incorporate intra- and inter-annual variation in chick survival to improve predictions. Observed variation in chick survival rates portends a significant opportunity to improve population management for bobwhites and other game birds. © 2019 The Wildlife Society     

Effects of Landscape Composition on Winter Survival of Northern Bobwhites

Abstract: In a manipulative experiment, we tested effects of select elements of landscape structure and composition on winter survival of northern bobwhites (Colinus virginianus) at Ames Plantation, Tennessee, USA. We hypothesized that abundance of closed canopy forested habitats (52% of the landscape) on Ames diminished usable space for bobwhite and provided usable space for a suite of important predators, thereby contributing to low winter survival. To test this hypothesis we divided a 2,217-ha portion of the property into 4 approximately equal areas. We altered landscape structure and composition by converting approximately 33% of the timber to early successional herbaceous plant communities on 2 treatment sites, which reduced percentage of landscape and edge density of closed canopy forest and increased percentage of landscape in early successional herbaceous communities, and left 2 control sites in their former composition. During one pretreatment year (1998–1999) and 3 posttreatment years (1999–2000, 2000–2001, 2001–2002), we estimated winter (15 Oct-10 Apr) survival on treatment and control sites from a radiomarked sample of 920 bobwhites. We used Cox Proportional Hazard models to test for effects of treatment (forest conversion) and covariates describing landscape structure and composition (% closed canopy forest, % early successional herbaceous, wooded edge density) on winter survival at multiple spatial scales. Winter survival on the treatment sites pooled across the 4 winter seasons was 41% compared to 32% for control sites. Additionally, for each 1 m/ha increase in closed canopy woods edge density within winter covey ranges, risk of mortality increased 0.3%. Our results suggest composition at the landscape scale and landscape structure at the local scale influence winter survival of bobwhite. Management strategies that alter composition and structure and increase usable space may be effective in mitigating winter mortality thereby altering population trajectories. Typical bobwhite management plans focus on improving quality of herbaceous vegetation structure within existing herbaceous patches, however, population processes may work at larger spatial scales influencing design and implementation of conservation programs.     

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.     

Home range and habitat selection of northern bobwhite coveys in an agricultural landscape

Northern bobwhites thrive in fine-grained landscapes with a diversity of early succession woodland, grassland, and agriculture-associated habitat types. Bobwhite conservation has proved challenging in the increasingly coarse-grained Midwestern landscape as simplified agricultural cropping systems are implemented at larger spatial scales. Regardless, managing agricultural landscapes on private lands is the primary opportunity to restore bobwhite populations in the Midwestern United States. Although bobwhite habitat requirements are well understood, habitat selection in contemporary Midwestern landscapes is not well understood, especially on private lands where populations are declining. We used compositional analysis to investigate second- (study area) and third- (home range) order habitat selection by radiomarked bobwhite coveys on 4 private land study areas in southwestern Ohio. Mean covey home range size was 26.1 ± 2.2 ha (n = 48). Although home ranges were established in areas with more grassland cover, bobwhites most strongly selected early succession woody habitat (e.g., fencerows and ditches) at all scales, and selection for grassland diminished between the study area and home range scales. Grassland selection varied among sites and was strongest on sites with more row crop area. Woodlots were avoided at the study area scale, but were selected within home ranges. Grassland cover, like that provided by contemporary conservation programs, is an essential component of bobwhite habitat in the Midwest, but our results suggest more emphasis should be placed on early succession woody cover. Woody cover associated with fencerows, ditches, and woodlots adjacent to food sources and breeding habitat will likely improve non-breeding season survival, which is an influential vital rate in northern populations. © 2012 The Wildlife Society.