Northern Bobwhite Populations Research Articles

Effects of management practices on Northern Bobwhite Colinus virginianus density in privately owned working forests across the Southeastern United States

Abstract Obtaining rigorous baseline density estimates of species of conservation interest is key when assisting landowners to achieve management goals on private lands. Northern bobwhite (Colinus virginianus) populations are declining throughout their range and despite being the focus of numerous private land conservation initiatives, baseline density estimates in privately owned pine forests are lacking. We sought to address this knowledge gap across the Southeastern United States by sampling 105 privately owned pine stands throughout 2018 to 2020 using observer point count and autonomous recording unit (ARU) sampling data. Using Bayesian hierarchical models, we investigated the influence of stand management (brush management or applied fire) on bobwhite density, as well as four landscape‐scale environmental variables. These included percentage cover of forest, herbaceous, agricultural or burnt land area across six different spatial scales ranging from 500‐m to 10‐km around each pine stand. Baseline density on sites with no management was estimated to be 2.24 coveys per 100 ha (1.00–5.03, 95% BCI), with little impact of applying brush management, but a trend for a positive effect of fire management (0.19, −0.01 to 0.38 95% BCI). This impact of fire was seen at both the stand‐scale, correlated with an increase in acreage of applied prescribed burn management, and across the greater landscape area, correlated with cover of burnt area within a 2‐km buffer around each site. There were also strong positive influences of herbaceous vegetation and a strong negative influence of forest cover on bobwhite density. Practical implication: our sampling efforts fill an important information gap regarding densities throughout private lands in the Southeastern United States. Our study also highlights the necessity of landscape scale planning for Northern Bobwhite conservation initiatives because the efficacy of conservation practices (i.e. prescribed fire and brush management) could be altered by the landscape surrounding the treated forest stand.

EXPLORING A PLANT-DIVERSITY HYPOTHESIS TO EXPLAIN HELMINTH PREVALENCE IN NORTHERN BOBWHITE (COLINUS VIRGINIANUS) IN TEXAS, USA.

Helminths, in particular eyeworms (Oxyspirura petrowi) and cecal worms (Aulonocephalus pennula), may be a factor influencing northern bobwhite (Colinus virginianus) populations in Texas. Previous research has shown a discrepancy in helminth infections between the Rolling Plains and Rio Grande Plains of Texas, US, potentially caused by differences in intermediate host distribution and abundance. We explored an alternative hypothesis centered on plant diversity, given that many plants possess phytochemicals with anthelmintic properties. We predicted that plant diversity would be greater and bobwhite diet more diverse in the Rio Grande Plains than the Rolling Plains, which in turn would potentially expose bobwhites to more plants with anthelmintic properties and therefore result in lower parasite prevalence and intensity. We conducted a literature review of plant diversity, anthelmintic plants, and bobwhite diet in Texas to explore this hypothesis. We also quantified the relationship between helminth prevalence in bobwhites and latitude. We documented trends for higher plant species richness, greater number of anthelmintic plants, and more diverse bobwhite diet in the Rio Grande Plains compared to the Rolling Plains. In addition, we documented a trend for increasing helminth prevalence with latitude for eyeworms but not cecal worms. Our study provides circumstantial evidence supporting the plant-diversity hypothesis and warrants experimental testing.

Evaluation of seasonal site-level demography and management for northern bobwhite using integrated population models

Understanding the effects of landscape management on northern bobwhite (Colinus virginianus) population growth requires information on seasonal- and stage-specific demographic parameters linked across the full annual cycle. We evaluated site-level seasonal dynamics and population growth of bobwhites in southwest Missouri and compared differences between three extensively and two intensively managed sites from 2016 to 2019. Extensively managed sites were continuous tracts of native prairie. Intensively managed sites were composed of smaller native and non-native grassland units interspersed with strip crops, food plots, and woody field borders. We radio-marked adults and broods to estimate survival and productivity, conducted spring whistle counts to estimate abundance and developed a two-season, two-stage, two-sex integrated population model to estimate population dynamics. The number of young hatched per female-incubated nest was greater on the three extensively managed sites compared to the two intensively managed sites. Six-month period survival of adults during the breeding season was also greater on the three extensively managed sites compared to the two intensively managed sites. One hundred-day juvenile breeding season survival varied among sites and was highest on Talbot, compared to juvenile breeding season survival on the other four study sites. Six-month, non-breeding season period survival was lowest on the two smallest extensively managed sites, Stony Point Prairie and Shelton Conservation Area compared to non-breeding season survival on the other three study sites. Annual changes in bobwhite abundance were weakly correlated with female fecundity, though this positive relationship was stronger on extensively managed sites. Intensively managed sites exhibited low mean fecundity and breeding season adult survival relative to those that resulted in a stable population. Populations across sites declined from 2016 to 2019 and estimates of annual population growth rates overlapped across sites. Differences between observed changes in bobwhite abundance and estimates of observed demographic rates at some sites suggest unmeasured processes such as movement or bias associated with data and model assumptions influenced estimated vital rates. Overall, our integrated population model was an effective tool for understanding site-level seasonal dynamics and population growth of bobwhites. Based on comparisons of demography between extensively and intensively managed sites, we suggest increased native grassland cover managed with prescribed fire, low intensity grazing, and high mowing may increase bobwhite nesting success and breeding season adult survival, however, achieving stable or increasing rates of population growth may also require increased juvenile breeding season and non-breeding season survival.

A maximum entropy and GIS approach to predict potential habitat for northern bobwhites in the Black Belt prairie physiographic region of Alabama

Northern bobwhite (Colinus virginianus) populations have sustained precipitous declines throughout their range. The North American Breeding Bird Survey for Alabama indicates a rate of decline of over 6% per year since 1966. Declining bobwhite populations have been associated with large-scale habitat loss and a reduction in habitat quality due to advances in ecological succession, intensive monoculture agriculture, and intensive timber management practices. Once a very diverse region, modern land-use practices throughout the Black Belt Prairie physiographic region have created a simplified landscape that have left few places where bobwhites can live and thrive. Despite extensive research on bobwhites, there is insufficient knowledge on the spatial distribution of bobwhite habitat on a regional scale, including the Black Belt Prairie physiographic region. Knowing the spatial distribution of suitable bobwhite habitat will allow conservation planners to prioritize efforts and direct limited resources to achieve conservation goals for the region. The goals of this study were to 1) evaluate the maximum entropy modeling approach for predicting northern bobwhite habitat in the Black Belt Prairie physiographic region, and 2) develop a northern bobwhite habitat suitability map for the Black Belt Prairie physiographic region. The results showed that deciduous 1.8 km (1.8 km is the dispersal distance of bobwhites) neighborhood was the most important habitat variable, followed by water 1.8 km neighborhood. Developed 1.8 km neighborhood was the most important anthropogenic variable, ranking third in overall importance. The resultant model denotes potential habitat in the region and forms the basis for using the maximum entropy and geographic information system approach to predict suitable habitat and prioritize areas for conservation.

Quail and rain in semiarid rangelands: Does management matter?

AbstractRainfall 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).

A Simulation Model of Sustained-Yield Harvest for Northern Bobwhite in South Texas

Recommended sustainable harvest rates for northern bobwhite (Colinus virginianus) vary greatly and range from 25% to 70% of the prehunt population. Because northern bobwhite populations have declined across their geographic range, determining sustainable harvest levels is critical for effective management. Our objectives were to use simulation modeling to identify sustainable rates of bobwhite harvest, probability of population persistence, and minimum viable population estimates. We also conducted a sensitivity analysis to evaluate the impacts of harvest on northern bobwhite populations in Texas, USA. We constructed a simulation model using Program STELLA 9.0 for a hypothetical northern bobwhite population on 800 ha in the South Texas Plains USA and modeled population dynamics to 100 years over a range of harvest rates (0–40%). A 20% harvest rate produced the greatest average yields (mean ± standard error = 231 ± 10 bobwhites harvested/year). Given a quasi-extinction criterion of ≤40 bobwhites (≤0.05 bobwhite/ha), a 30% harvest rate resulted in a high probability of quasi-extinction (PE = 0.75) within 47.8 ± 2.3 years. A 40% harvest rate was not sustainable (PE = 1.0), with quasi-extinction occurring within 15.5 ± 2.6 years. Harvesting northern bobwhite populations in the South Texas Plains at rates of 20−25% of the prehunt population should maximize long-term harvest while minimizing the probability of population extinction. Spring densities of 0.60−0.80 bobwhite/ha may represent minimum viable spring densities for northern bobwhite populations in the South Texas Plains as these are the densities associated with sustainable 20-25% harvest rates. Harvest rates >30% are likely to be excessive with respect to long-term population persistence for northern bobwhite populations in the South Texas Plains.

Evaluating Release Strategy for Translocated Northern Bobwhites in Cross Timbers Ecoregion of Texas: A Pilot Study

Northern bobwhite (Colinus virginianus) population decline is largely driven by the loss, fragmentation, and degradation of grassland habitats. Translocation is used to reintroduce or augment populations in fragmented landscapes where natural dispersal is inhibited. Northern bobwhites have been successfully translocated in the southeastern portion of their range, but outcomes of translocations in western ranges have been mixed. Our objective was to conduct a pilot study to test the feasibility of translocating northern bobwhites to a restored, but isolated, habitat in the Cross Timbers ecoregion of Texas, USA and to evaluate the influence of release strategy for improving northern bobwhite site fidelity and survival post-release. The release property was restored through brush management, native species seeding, and proper grazing management. We trapped and translocated 84 northern bobwhites from source populations in the Rolling Plains and Edwards Plateau ecoregions during March 2015. Coveys were assigned to either delayed or immediate release treatment. We radio-collared all hens (n = 40; 11 adults; 29 juveniles) and evenly divided the sample between delayed and immediate releases. Delayed release coveys were held on the release site for 4 weeks in a Surrogator® (Wildlife Management Technologies, LLC). We trapped and radio-collared resident hens (n = 15) in March and monitored all hens through breeding season (March–August; 180 days). We implemented a 2-state (alive or dead) multistate model in Program MARK to analyze survival as a function of the release treatment, resident status, and age. We found no evidence that survival differed between translocated and resident hens (β = 0.48, standard error [SE] = 0.38), release treatments (β = 0.10, SE = 0.40), or age (β = -0.16, SE = 0.54). Daily survival for all hens was 0.99 (SE = 0.009) and breeding season survival was 0.19 (SE = 0.08). Four (20%) immediate, 2 (10%) delayed release, and 0 resident hens dispersed off-property. Translocated and resident hens survived at similar rates, indicating that translocation may be a feasible management strategy for augmenting a northern bobwhite population on restored habitats in the Cross Timbers ecoregion although overall survival was low. We did not find evidence that delayed release improved daily survival post-release, but our small sample size may have prevented us from detecting a difference. However, delayed release birds were effectively sheltered from predation during peak raptor migration. Additional research is needed to fully understand population dynamics and implications of release strategy for translocated northern bobwhite.

Adaptive Management Facilitates Increase in Northern Bobwhite Populations

Adaptive resource management (ARM) is an approach to managing that allows decision makers to learn about a system and subsequently change management actions based on new information about system processes (i.e., adapt) to better meet fundamental objectives. This is not to be confused with changing management actions when the state of the system changes. For example, changing a harvest regulation when populations decline is not ARM. This dynamic decision making may be fortuitously optimal, but if the effect of harvest is uncertain then changing regulations may be suboptimal—for example, weather may have caused the decline. Adaptive resource management can be implemented along a spectrum of passive to active to reduce system uncertainty. Active ARM is when explicit hypotheses are posited then implemented to test them, and monitoring occurs to elucidate whether the effect of the management action achieved a given result. Passive ARM uses current management practices, natural variation in the system, and monitoring to reduce uncertainty. Even though northern bobwhite (Colinus virginianus) have been studied for a century, uncertainty regarding optimal management strategies still exists. The Albany Quail Project (AQP) has used both modes of ARM to learn about northern bobwhite populations to better meet the hunting objectives of stakeholders. Between 1992 and 2019 the AQP radio-tagged 5,182 unique individuals and banded an additional 5,008 birds on the primary study area near Albany, Georgia, USA. Additionally, 1,724 nests have been monitored and population surveys conducted in the spring and autumn. Active ARM occurred with tests of supplemental feeding, hardwood cleanup, and predator control whereas passive ARM was used to learn about prescribed fire regimes, brood habitat preferences, small mammal cycles, and raptor migrations. We built an integrated population model (IPM) that combined known-fate survival data, nesting records, dead recoveries from harvest, and population surveys to model the system. The preliminary results of the IPM demonstrated that populations have increased during the project. The 5 most abundant autumn populations have occurred in the most recent 10 years of the project when bobwhite populations throughout their range have continued to decline. Unlike typical ARM applications, the AQP has not had an explicit model to predict consequences of future management actions; nonetheless, the essence of ARM has been followed. Since its inception uncertainty has been reduced, management actions have been changed, and bobwhite populations have responded. Improvements to AQP and similar projects could include explicit hypotheses and predictive models about the system

Effects of Climate Change on Northern Bobwhite Nesting Chronology and Clutch Size

Widespread changes to breeding bird phenology in response to climate change have been apparent in North America for several decades. While the impact of an earlier breeding season may be minimal by itself, changes in community-level interactions can be greatly influenced because of varying responses to climate change in different trophic levels. Climate change has been shown to alter the onset of breeding season and chick survival, and lead to population declines for game birds in high latitudes, at high elevations, and on the periphery of their range. The topic of climate change in relation to northern bobwhite (Colinus virginianus; hereafter, bobwhite) populations has attracted interest in the past 2 decades. Some researchers have hypothesized that climate change has the potential to cause the breeding season to initiate sooner and have a shorter duration. Using a 29-year dataset (1992–2020) with 1,171 individual bobwhites, we analyzed how temperatures prior to the breeding season affected the timing of nest initiation and clutch size, and how the length of the breeding season varied over time. We determined that the average minimum daily temperatures 30 days prior to the breeding season warmed by 0.07° C/year from 1992–2020. For any given year, we found that nest initiation could occur 1.12 days earlier for every 1° C increase in temperature. Overall, we determined that the timing of the nesting season had not changed from 1992–2020. The overall average breeding season length (135 days) or last average initiation date (27 Aug) did not change over the course of our study. We did not find that clutch sizes have changed over time and they were not correlated to pre-laying temperature. We attribute the lack of significant change in nesting chronology to plasticity of populations within the core of the range and the intensity of bobwhite management on the landscape.

Northern Bobwhite Demographics and Resource Selection Are Explained by Prescribed Fire with Grazing and Woody Cover in Southwest Missouri

Understanding the effects of landscape management on northern bobwhite (Colinus virginianus; hereafter, bobwhite) population growth requires information about seasonal- and stage-specific demographic parameters linked across the annual cycle. We review results to date from 3 years (2016–2018) of an intensive field study evaluating drivers of bobwhite population dynamics and resource selection during the breeding and non-breeding season in southwest Missouri, USA using data from adult and juvenile bobwhite fitted with radio-transmitters. Land cover of our study sites ranged from large blocks of native grasslands maintained with prescribed fire and grazing to more traditional management resulting in small patches of grasslands interspersed with food plots, disked idle areas, and woody cover. During the breeding season, relative probability of selection by broods increased in relation to proportion of native grass managed by grazing and burning and proportion of cropland. Brood survival was also greatest on native grasslands burned and grazed within the past 2 growing seasons. During the fall and winter, relative probability of selection by adults increased as woody edge density increased. Fall and winter survival increased as distance from trees increased and decreased as distance to shrubs increased. Our integrated population model indicated that the number of young hatched per female and adult breeding season survival were greatest on sites with the most native grassland managed by prescribed fire with grazing. However, non-breeding season survival was greater on sites with more agriculture or food plots and woody cover. Abundance declined across all sites from 2016 to 2019. Our work suggests that native grasslands managed by prescribed fire with grazing can provide quail habitat superior to traditional management that strived for a mixture of agriculture, woody cover, and grassland. The combination of conservation grazing and fire in native grasslands interspersed with shrubs may provide the greatest chance for bobwhite populations to persist in southwest Missouri and similar landscapes.

Exploring a Plant-Diversity Hypothesis to Explain Helminth Prevalence in Northern Bobwhite in Texas

Helminths, in particular eyeworms (Oxyspirura petrowi), may be a factor influencing northern bobwhite (Colinus virginianus; hereafter, bobwhite) populations in Texas, USA. Mean eyeworm prevalence in Texas appears to be greater in the Rolling Plains (55.1%) than the Rio Grande Plains (16.4%), a pattern generally attributed to possible differences in the occurrence of insects, the intermediate hosts of eyeworms. We explored an alternative hypothesis centered on plant diversity. Many plants possess phytochemicals with anthelmintic properties. Because wild animals suffering from parasitic infestations are capable of self-medicating via diet selection, organisms foraging in diverse communities may be expected to possess lower parasite levels. We predicted that plant diversity would be greater and bobwhite diet more diverse in the Rio Grande Plains than the Rolling Plains, which in turn would potentially expose bobwhites to more plants with anthelmintic properties and therefore result in lower parasite prevalence. We conducted a literature review of plant diversity, anthelmintic plants, and bobwhite diet in Texas to explore this hypothesis. Our results indicated that 1) plant diversity was higher (24–96%), 2) the number of anthelmintic plants greater (33%), and 3) bobwhite diet more diverse (120%) in the Rio Grande Plains compared to the Rolling Plains. We documented a mean (± standard error) eyeworm prevalence of 16.4 ± 7.27% in the Rio Grande Plains (n = 4 sites) and 55.05 ± 2.93% in the Rolling Plains (n = 20 sites). The mean cecal-worm prevalence was documented at 74.8 ± 18.21% in the Rio Grande Plains (n = 5 sites) and 79.79 ± 2.12% in the Rolling Plains (n = 19 sites). Regarding plant diversity, the Rio Grande Plains contained more potential anthelmintic plants (n = 96 species) than the Rolling Plains (n = 72 species). In cross-referencing these plants with the bobwhite diet, we found that 23 plants with possible anthelmintic properties had been documented in the bobwhite diet in the Rio Grande Plains, whereas only 17 such plants were documented in the bobwhite diet in the Rolling Plains. Our study provides circumstantial evidence for the plant-diversity hypothesis and warrants experimental testing.

Translocating Wild California Valley Quail to Texas: An Evaluation of Survival, Dispersal, Tracking Efficacy, and Roost Preference

Quail translocations are becoming increasingly popular in regions of suitable habitat where local quail populations have declined. In northeastern Texas, USA, northern bobwhite (Colinus virginianus) populations have drastically declined for over a century and have reached undetectable levels in many areas. As a result, the number of quail hunters and quail conservation funding have also declined. California valley quail (Callipepla californica; hereafter, valley quail) have increased across their range and have been translocated to many states and countries. Thus, the goal of this study was to determine whether translocating wild valley quail to Texas was feasible, and evaluate their survival, dispersal, roost location preference, and potential predator impacts. We translocated 748 wild valley quail from Idaho, USA to northeastern Texas in 2019 and 2020. We collected quail location data from very high frequency (VHF) and digital transmitters. Motion-triggered cameras, scent stations, simulated nests, and raptor transects were used to record predator presence and potential predator impacts. Survival of birds with tracking devices was 63% (VHF) in 2019, and 38.8% (VHF) and 92.5% (digital tag) in 2020. Survival was greater for quail with digital transmitters. Median dispersal distance was 633.5 m in 2019 and 246.6 m in 2020 for valley quail with VHF transmitters, and 310.4 m for quail with digital transmitters. Minimum convex polygon area medians were 4.3 ha in 2019 and 3.1 ha in 2020 for quail with VHF transmitters, and 16.1 ha in 2020 for quail with digital transmitters. Roost sites were primarily in young stands of oak trees. Median simulated nest survival was 2 days (minimum [min] = 1, interquartile range [IQR] = 2–5.4, maximum [max] = 23) in 2019, and 7.5 days (min = 2, IQR = 4.5–15.2, max = 23) in 2020. The most frequent mammalian predators observed were raccoons (Procyon lotor), feral hogs (Sus scrofa), and white-tailed deer (Odocoileus virginianus). Red-tailed hawks (Buteo jamaicensis) were the most frequent aerial predator. We completed the first documented translocation of wild California valley quail to Texas, demonstrating it is feasible. Future translocation may benefit from translocating more birds over a longer period of time, with more consistent methodology. The establishment of a sustainable population may require ≥7 years of translocation at a rate of 500 birds per year with >2,000 ha of suitable habitat.

Survival, Movement, and Habitat Use of Translocated Northern Bobwhite in Texas

For decades there has been a noticeable decline in northern bobwhite (Colinus virginianus; hereafter, bobwhite) populations. Few studies have assessed the survival of translocated bobwhite. We evaluated the effectiveness of reintroduction of bobwhite into the Texas (USA) Parks and Wildlife Department’s Gus Engeling Wildlife Management Area (GEWMA), where they had been extirpated but now have suitable habitat. Before reintroduction, GEWMA was surveyed (spring call counts) to make sure no bobwhite were present. Forty-six bobwhite were trapped from March–April 2019 in South Texas, banded, bled, radio-tagged, transported to GEWMA, and released. In addition, 17 bobwhite were trapped banded, bled, radio-tagged, and released back into the source population as a control for comparison of movements, reproduction, and survival estimate differences between the source and released bobwhite populations. During July 2019, 3 broods (24 bobwhite) were trapped and translocated from a South Texas ranch to the GEWMA. Survival for bobwhite released at GEWMA was 37.0% through 1 July 2019 and 70.6% for bobwhite left on the ranch in South Texas. Three nests were found at GEWMA while none were found on the ranch in South Texas. Movement distances between daily locations for males and females did not differ at GEWMA or at the ranch in South Texas; however, there was a significant (P ≤ 0.001) difference in daily movement for bobwhite at GEWMA and the South Texas ranch. Female bobwhite at GEWMA moved 5.4 times the distance of female bobwhite in South Texas and male bobwhite at GEWMA moved 5.9 times the distance of male bobwhite in South Texas. Bobwhite at GEWMA were located in woody cover only 24.2% of the time, whereas bobwhite in South Texas were located in woody cover 76.1% of the time. The greater daily movement and less use of woody cover for bobwhite at GEWMA probably contributed to their lower survival.

Estimating Northern Bobwhite Density in Privately-Owned Forests Across the Southeast

Rigorous density estimates can inform management, conservation planning, and policy decisions. Northern bobwhite (Colinus virginianus; hereafter, bobwhite) populations are declining throughout their range, including the southeastern United States. Numerous private land conservation initiatives are underway to restore bobwhite populations in these areas, but baseline estimates of density spanning privately owned forests are sparse. This information gap makes it difficult to evaluate the population-level effects of these conservation programs or develop expectations for timelines to reach population targets. We sought to understand baseline densities across privately owned pine forests in the southeastern United States in areas targeted for bobwhite conservation. We sampled 138 pine stands a total of 286 times across Alabama, Florida, Georgia, North Carolina, and South Carolina from 2018 to 2020 using autumn distance sampling point counts. We sampled 110 stands that were either planned or applied U.S. Department of Agriculture, Natural Resources Conservation Service (NRCS) management contracts, specifically Working Lands for Wildlife (WLFW) Northern Bobwhite partnerships or similar Environmental Quality Incentives Program contracts. The WLFW contracts were solely in focal counties identified in the National Bobwhite Conservation Initiative 2.0 plan and by cooperating state wildlife agencies. Contracts were on average 17.4 ha (SD = 27.0). We also sampled 28 areas with extensive (>200 ha) and intensive (e.g., at least every 3 years for the last ~10 years) habitat management for bobwhite. We used a hierarchical distance sampling model to estimate density. Density was lowest in North Carolina and South Carolina. Densities in Alabama were slightly greater, and greatest densities were in Georgia and Florida. However, the majority of observed densities were 2 coveys/40 ha or below, and all were below 4 coveys/40 ha. Large and intensively managed sites on average had 4 times greater density compared to smaller contracts. Specific densities will be reported in the future. Our sampling efforts fill an important information gap regarding densities throughout private lands in the southeastern United States. Our models indicate that bobwhite densities are generally low in pine forests of the Southeast even in counties identified as having the greatest conservation potential. The relatively greater densities at large and intensively managed sites illustrate the need for more intensive landscape-scale planning when implementing private land conservation. Pending research will compare densities at planned and applied NRCS contracts in the context of landscape-scale habitat amount.

Northern Bobwhite Survival and Productivity in Relation to Food Supplementation

Northern bobwhite (Colinus virginianus; hereafter, bobwhite) populations have experienced a 3.4% decline annually nation-wide from 1966 to 2018. Limitations on resources, such as food, can regulate population growth. Supplemental food could alleviate resource limitation by raising carrying capacity, leading to increased survival and breeding productivity. Studies have shown higher survival rates and higher nest production when food is supplemented; however, repeating experiments in different contexts allows for strong inference. Our objectives were to assess how supplemental food influenced survival and breeding productivity of resident and translocated bobwhite during a 2-year study on public lands in Leon County, Florida, USA within the Apalachicola National Forest. In accordance with the food limitation hypothesis, we predicted that provisioning of supplemental food would have a positive influence on survival rates and nest productivity. We split the study site into 4 approximately 400-ha zones and randomly assigned 2 treatment (fed) and 2 control (unfed) replicates. Treatment and control zones were flipped during the second field season. Treatments received approximately 1.75 bushels of milo (Sorghum bicolor)/acre 2 times/month year-round via broadcast spreader. We radio-marked 205 bobwhites (102 treatment, 103 control) from February 2019 through October 2020. Individuals were tracked 3–4 times/week for location and survival via radio-telemetry to estimate the breeding season survival and reproduction rates. We estimated survival rates using the Kaplan-Meier product limit estimator. The survival rate during the breeding seasons was higher on average for treatment zones (x̄ = 0.38, standard error [SE] = 0.040) than for control zones (x̄ = 0.29, SE = 0.045). We also observed that 79% of nests found were located in treatment zones compared to 21% in control zones. Our results suggest that food supplementation can improve survival rates and nest production of bobwhite in a food-limited landscape.

Breeding Season Survival and Reproduction in a High-Density Bobwhite Population: A case study

The demographic behavior of northern bobwhite (Colinus virginianus; hereafter, bobwhite) populations at high densities could provide important insights into why bobwhite populations fluctuate. Therefore, we documented breeding season demographics of bobwhites to understand how prebreeding density influenced reproductive effort and postbreeding density on an intensively managed property in Leon County, Florida, USA, 2002–2006. We estimated prebreeding bobwhite density each April using multi-observer strip-transects and postbreeding densities each November using covey call grid surveys. We radio-tagged 217 bobwhites in March and located bobwhites at least 5 days/week, 15 April–30 September to determine vital rates. Prebreeding density ranged from 1.5–8.6 birds/ha, peaking in 2002, declining through 2005, then increasing in 2006. Breeding season survival was 0.55, 0.17, 0.20, and 0.59, and nesting rate was 0.47, 0.67, 0.80 and 0.89, 2002–2005, respectively. Postbreeding density ranged from 5.2–13.6 birds/ha, also peaking in 2002 and declining through 2004 before increasing beginning in 2005 and 2006. High breeding season survival and nesting success (>0.55) resulted in greater chick production during periods of population growth. Nesting rate was inversely related to prebreeding density. Declines in bobwhite nesting rate at high prebreeding densities appeared to regulate population growth near population peaks. Lower adult survival and nesting success appeared to cause population declines. We suggest density-dependent intraspecific competition limited population growth at high bobwhite densities by reducing nesting rate while predation of adults and nests explained population fluctuations.

Exploring the Relationships between South Texas Northern Bobwhite Populations and Cecal Worms via System Dynamics

Community ecology historically focused on plants and free-living organisms; however, problems such as defining habitat boundaries and obtaining adequate sample sizes arise when evaluating such communities. The unique nature of host-helminth systems allows parasite community ecologists to avoid these problems when testing ecological hypotheses. Unlike free-living communities that have artificially constructed boundaries, parasite communities have well-defined unambiguous boundaries within host individuals. Due to the inherently complex and dynamic nature of ecological systems, traditional experimental methods often require expensive, long-term trials beyond investigators’ time and resource budgets. Conversely, a system dynamics approach facilitates learning about such systems via simulation of ecosystem processes integrated with historical data (both quantitative and qualitative). Relatively few studies focus on parasites in South Texas, USA, although research on avian host-parasite systems has shown that parasites can potentially regulate host populations. The northern bobwhite (Colinus virginianus; hereafter, bobwhite) is a game species of ecological, economic, cultural, and recreational importance in Texas that has been experiencing a long-term, widespread decline. To holistically examine the bobwhite-helminth system in South Texas, we created a system dynamics model capturing the feedback relationships between a South Texas bobwhite population, a grasshopper (family Acrididae) population, and the corresponding cecal worm (Aulonocephalus pennula) populations on a hypothetical 1,000-acre ranch in South Texas. The model structure, constructed in Vensim® PLE 7.2 software (Ventana Systems, Inc.), integrates the hypothesized biotic and abiotic drivers (precipitation, parasite load, insect abundance, and quail density) unique to the host-helminth system over 7 years (2012–2019). Our specific objectives were to 1) develop a working baseline model to replicate the synergistic population dynamics among bobwhite, grasshopper, and cecal worm populations and then 2) test hypotheses about each population’s boom-and-bust cycles resulting from environmental stressors (e.g., drought). Applications of the model can provide landowners and natural resource managers with a better understanding of the complex dynamics occurring among bobwhite, grasshopper, and cecal worm populations in South Texas.

Examining a Habitat-Weather Threshold for Northern Bobwhite Populations in the Southwestern United States

In semiarid portions of the northern bobwhite (Colinus virginianus; hereafter, bobwhite) geographic distribution, weather is a strong driver of interannual abundance. However, the strength of this relationship may depend on habitat amount. Given this habitat–weather dependence, there is likely to be a threshold value for habitat that determines how strongly a bobwhite population responds to weather. Our objective was to evaluate the relationship between habitat amount and the relative influence of weather on bobwhite abundance in Texas and Oklahoma, USA and determine a potential land-cover threshold value. We collected bobwhite abundance and land-cover data from the Breeding Bird Survey and National Land Cover Database, respectively, for 2 time periods which corresponded to historical lows (2012–2013) and highs (2015–2016) of bobwhite abundance within this region. We reclassified land cover into grassland, shrubland, pastureland, cropland, forest, and urban cover, and combined grassland and shrubland categories to represent bobwhite habitat. We used weighted linear regression to model the difference between mean bobwhite abundance between each time period as a function of habitat amount, hypothesizing a positive, linear relationship given the theorized greater influence of weather on populations within higher habitat amounts. To evaluate a potential habitat threshold, we modeled mean bobwhite abundance, for each time period, and all individual land-cover variables using a generalized additive model with a negative binomial distribution. We detected a positive, linear relationship between habitat amount and the difference between high and low bobwhite populations (r2 = 0.30), per our hypothesis. Models of land-cover variables differed between low- and high-abundance time periods. The time period of lower abundance (2012–2013) model included all land-cover variables except cropland and showed significant positive, linear relationships with grass and hay cover, and negative, linear relationships with forest and urban cover. Shrubland cover was the only nonlinear term, increasing to approximately 50–60% cover, then decreasing sharply with increasing cover. Deviance explained for this model was 41.2%. For the period of high abundance (2015–2016) the model explained approximately 25% of the deviance and was reduced to only negative, linear relationships with forest and urban cover. Our results provide some evidence toward the habitat–weather threshold hypothesis. Additionally, while no land-cover values showed a threshold-like relationship with bobwhite abundance, we did document differences in variable selection for each time period. Stressors on bobwhite habitat seem to have a more dramatic impact on bobwhite populations than available habitat, especially in periods of higher abundance, whereas periods of lower

An integrated population model to project viability of a northern bobwhite population in Ohio

AbstractIncreased variation in interannual weather due to climate change can exert a powerful influence on the population dynamics of a species. Understanding the influence of severe weather is important for managing weather‐sensitive species. While best management practices target vital rates that are affected by weather, focusing on a single vital rate may not be sufficient if other vital rates are secondarily limiting. A comprehensive modeling framework to forecast future population dynamics while incorporating weather scenarios and vital rate variation within observed ranges that can be affected by management actions are necessary. A potential approach is to combine an integrated population model (IPM) with a population viability analysis (PVA) to generate novel insights about population dynamics. We used the northern bobwhite (Colinus virginianus), a rapidly declining gamebird sensitive to snowfall along the northern extents of the species' range, to demonstrate the utility of a coupled IPM‐PVA framework for projecting the response of a population to weather, management, and changes in vital rates. We created an IPM using two sources of count data spanning seven years, five years of winter survival data, and two years of breeding season demographics for a declining bobwhite population in southwestern Ohio during 2007–2015. Quasi‐extinction probability at the end of the decadal projection during 2019–2029 was 0.384–0.410 for mild, average, and severe winter weather scenarios. Quasi‐extinction probability declined to 0.326 with 20% improvement in nest success and summer survival rates. A concurrent 20% increase in winter survival further reduced quasi‐extinction probability to 0.263, which is a ˜36% reduction in quasi‐extinction probability compared with the baseline scenario with no changes in vital rates. These results suggest that long‐term viability of this population may depend on extensive management of winter habitat to improve survival but will also require management actions to improve fecundity after severe winters. Our modeling approach demonstrated how IPMs can be used to project population responses to future weather conditions and overcome some of the pitfalls of traditional PVA. The coupled framework presented here can serve as a tool for managers to make climate‐informed management decisions.

Ecological risk assessment of the effects of neonicotinoid insecticides on northern bobwhites (Colinus virginianus) in the South Texas Plains Ecoregion.

Neonicotinoid insecticides are among the latest class of insecticides that can have harmful effects on birds. Approximately 30 000 kg of neonicotinoid insecticides are applied annually to 429 100 ha of row-crop fields within the South Texas Plains Ecoregion, Texas, USA. Various studies have demonstrated that treated seeds can be highly toxic to northern bobwhites, with the consumption of only 20 corn seeds causing a fatality. Similarly, other studies have indicated that neonicotinoid insecticides can reduce arthropod populations-a substantial prey base for northern bobwhites, especially during the breeding season-by approximately 60%. Our objective was to conduct an ecological risk assessment of neonicotinoid insecticides' impact on northern bobwhite (Colinus virginianus) populations in the South Texas Plains Ecoregion. We estimated that juvenile and adult northern bobwhites could intake from 7.32 to 27.0 mg/kg/day and from 10.0 to 37.5 mg/kg/day of neonicotinoid insecticides, respectively, which can cause adverse effects on growth, reproductive output, and long-term survival. Our study determined that the application of 30 000 kg of neonicotinoid insecticides annually in the South Texas Plains Ecoregion harms the region's northern bobwhite that are exposed to neonicotinoids. Integr Environ Assess Manag 2022;18:488-499. © 2021 SETAC.