Adaptive Harvest Management Research Articles

Rapid population response to a hunting ban in a previously overharvested, threatened landbird

AbstractEmpirical data are essential to assess the outcomes of management decisions in the context of adaptive management. We used flyway‐level population indices of a declining game bird to assess population changes after introducing hunting management measures as part of the European Union (EU)‐wide Adaptive Harvest Management mechanism (AHMM). In one flyway, a full hunting ban led to the start of population recovery; numbers increased by 25% in 2 years and the 10‐year population trend improved from “moderate decline” to “stable.” In the other flyway, harvest was only reduced (allegedly by 60% although statistics from key countries were incomplete), and numbers continued to fall (−15% decline). Our study shows positive results of the leading AHMM for a landbird in Europe and provides empirical evidence of the speed of population response and the timeframe needed for change to occur and to be detected. It showcases the successful application of policy mechanisms underpinned by science.

Habitat management carried out by hunters in the European turtle dove western flyway: Opportunities and pitfalls for linking with sustainable hunting

As described in many farmland birds of Europe, habitat loss is one of the main factors explaining the decline of the European turtle dove (Streptopelia turtur), a migratory columbid which breeds in the Western Palaearctic and winters in Africa. In the countries belonging to the western flyway (which host around 40–50% of the European breeding population), the species was hunted before the implementation of a moratorium in recent years, and it is known that habitat management is conducted to favour game and wildlife. Through a questionnaire we investigated the habitat management conducted in hunting grounds of France, Portugal and Spain (931 respondents), and the measures that may favour turtle doves. The vast majority of respondents were totally or partially in charge of game management (98%), but less than 50% were responsible for decisions regarding farming or forestry. The most frequent measures were supplementary food (73% of respondents), water provision (68%), forest management (50%) and agricultural management (47%). Land interventions were conducted in a high proportion of grounds, but at limited scale (<50 ha/hunting ground). In most cases, the management was self-funded by hunters and game managers. Habitat management measures were rarely targeted exclusively to the turtle dove; interventions were, in contrast, frequently part of management targeting various species simultaneously. Grounds with a tradition of higher number of hunted doves were those more likely to target the species in their management. The likelihood of implementing management tools was mainly linked to variations in hunting pressure rather than to perceptions of turtle dove population trends. As the turtle dove is favoured by the ecotone between woodland and farmland, it is crucial to promote and reward measures beyond food and water provision, involving agricultural and forest management, ideally accompanied by species’ monitoring in hunting grounds. As the current Adaptive Harvest Management Framework promoted by the European Union aims to link hunting opportunities with habitat enhancements, hunting grounds could be crucial to improve turtle dove habitats at large scale and help reversing current population trends.

Movement dynamics influence population monitoring and adaptive harvest management strategies in migratory birds

Informed population monitoring efforts are essential for sound management of harvested species, and adaptive strategies that provide detailed information to monitoring efforts often require data inputs from complimentary sources. Movement ecology information is seldom directly incorporated into population monitoring or adaptive harvest management strategies, yet can provide valuable information on species distributions, emigration and immigration rates, and aid in determining optimal population monitoring timing. The Rocky Mountain Population (RMP) of Sandhill Cranes is a harvested population subject to a stringent adaptive harvest management framework and an annual aerial survey to estimate population abundance, but movements of Sandhill Cranes during survey windows, and subsequent changes to harvest quotas based on their movement and distribution have not been investigated. We used seven years of GPS tracking data to estimate state-specific emigration and immigration rates, using a Bayesian multi-state capture-recapture model, among states within the RMP distribution to understand how seasonal crane movements may influence optimal aerial survey timing. We then leveraged these transition probabilities in conjunction with aerial survey count data to model how changes in aerial survey timing and movement-informed crane distribution would influence the current RMP Sandhill Crane adaptive harvest management model resulting in estimated changes to harvest allocation among states based on Sandhill Crane movement. We found that Sandhill Crane emigration from northern states began to increase the week of the aerial survey in late September, and continued to increase as autumn migration progressed into October. As expected, immigration to southern states began as emigration from northern states increased. Importantly, little movement among states occurred prior to the current aerial survey design timing. Overall, we found that current survey timing and shortly thereafter (∼1 week) did not greatly influence estimates of Sandhill Crane distribution, and did not greatly influence the harvest reallocation to each state until mid to late October (range of −42–+52 tag allocation change), much later than the current survey design would allow. Using GPS locations, we found that optimal population monitoring efforts could be improved to account for both detection and seasonal movements, while minimally influencing current adaptive harvest management strategies to stakeholders. Linking movement ecology with population monitoring efforts and subsequently adaptive harvest management strategies yields insightful information that can be beneficial for conservation planning, decision-making, and optimal species management of a migratory bird.

Assessing the value of monitoring to biological inference and expected management performance for a European goose population

Abstract Informed conservation and management of wildlife require sufficient monitoring to understand population dynamics and to direct conservation actions. Because resources available for monitoring are limited, conservation practitioners must strive to make monitoring as cost‐effective as possible. Our focus was on assessing the value of monitoring to the adaptive harvest management (AHM) programme for pink‐footed geese Anser brachyrhynchus. We conducted a retrospective analysis to assess the costs and benefits of a capture–mark–resight (CMR) programme, a productivity survey and biannual population censuses. Using all available data, we fit an integrated population model (IPM) and assumed that inference derived from it represented the benchmark against which reduced monitoring was to be judged. We then fit IPMs to reduced sets of monitoring data and compared their estimates of demographic parameters and expected management performance against the benchmark IPM. Costs and the precision and accuracy of key demographic parameters decreased with the elimination of monitoring data. Eliminating the CMR programme, while maintaining other monitoring instruments, resulted in the greatest cost savings, usually with small effects on inferential reliability. Productivity surveys were also expensive and some reduction in survey effort may be warranted. The biannual censuses were inexpensive and generally increased inferential reliability. The expected performance of AHM strategies was surprisingly robust to a loss of monitoring data. We attribute this result to explicit consideration of parametric uncertainty in harvest‐strategy optimization and the fact that a broad range of population sizes is acceptable to stakeholders. Synthesis and applications. Our study suggests that existing or potential monitoring instruments for wildlife populations should be scrutinized as to their cost‐effectiveness for improving biological inference and management performance. Using Svalbard pink‐footed geese as a case study, we show that the loss of some existing monitoring instruments may not be as adverse as commonly assumed if data are jointly analysed in an IPM. Finally, regardless of the monitoring data available, we suggest that conservation strategies that explicitly account for uncertainty in demography are more likely to be successful than those that do not.

Winter Survival of Female Ring‐Necked Ducks in the Southern Atlantic Flyway

ABSTRACTNorth American waterfowl harvest regulations are largely guided by the status of breeding populations. Nonetheless, understanding the demographics of wintering waterfowl populations can elucidate the effects of hunting pressure on population dynamics. The ring‐necked duck (Aythya collaris) breeds and winters in all North American administrative flyways and is one of the most abundant and most harvested diving ducks in the Atlantic Flyway. But few studies have investigated the winter ecology of ring‐necked ducks. We used a known‐fate analysis to estimate period survival probability using data from 87 female ring‐necked ducks marked with satellite transmitters in 2 regions of the southern Atlantic Flyway during winters of 2017–2018 and 2018–2019. Winter (128‐day) survival probability was higher for individuals in the Red Hills region of southern Georgia and northern Florida (0.875, 95% CI = 0.691–0.952) than individuals in central South Carolina (0.288, 95% CI = 0.082–0.514). We attribute the regional disparity in winter survival probabilities to differences in hunting pressure, which are reflected in the number of harvests we observed in each region. Our findings warrant further investigation into regional variation in winter survival of southern Atlantic Flyway ring‐necked ducks, and, specifically, the relationship between variable harvest pressure and winter survival and its influence on ring‐necked duck population dynamics and adaptive harvest management decisions. © 2020 The Wildlife Society.

A systematic review of adaptive wildlife management for the control of invasive, non‐native mammals, and other human–wildlife conflicts

Abstract We are entering an era where species declines are occurring at their fastest ever rate, and the increased spread of non‐native species is among the top causes. High uncertainty in biological processes makes the accurate prediction of the outcomes of management interventions very challenging. Adaptive management (AM) offers solutions to reduce uncertainty and improve predictability so that the outcomes of interventions can continuously improve. We quantitatively assess the extent to which AM is used for managing vertebrates, with a focus on invasive non‐native species (INNS). Using the Web of Science, we evaluated 3992 articles returned by the search terms ‘adaptive management’ or ‘adaptive harvest management’ against seven recommended elements of AM (engagement with stakeholders, defining objectives, forecasting and estimating uncertainty, implementing management, monitoring populations, adjusting management in response to monitoring, and improving forecasting and reducing uncertainty in response to monitoring populations). The use of AM for vertebrates was reported in 56 (1%) of the evaluated studies; including four for managing INNS. Of these, ten studies excluding INNS and no studies of INNS management implemented all seven recommended elements of AM. Those elements infrequently implemented were as follows: the use of analysis or models to forecast and represent uncertainty (44%) and the feedback of monitoring data to improve forecasting and reduce uncertainty (25%). Complete active AM has rarely been implemented and reported for managing INNS, despite the significant advantages it offers. Among studies purporting to have implemented AM, most did not use analyses or models to forecast and represent uncertainty, while most defined objectives, implemented management, and monitored populations. Improvements to ongoing control programmes and much broader adoption of the AM approach are required to increase the efficiency and success of INNS management campaigns and reduce their negative impacts on native species.

Where to go goose hunting? Using pattern-oriented modeling to better understand human decision processes

ABSTRACTTo predict hunting pressure at a regional level for the adaptive harvest management of a European goose population, we created a predictive model within an existing agent-based model framework. In this paper, we outline the inputs, outputs, and learning from developing this model, using pattern-oriented modeling (POM), to predict the regional distribution of goose hunting locations. Our results showed that social aspects (e.g., crowding, how far hunters are prepared to travel) may influence hunter decisions when choosing hunting locations. However, access to multiple hunting locations and knowledge of goose behavior and likely foraging areas were more important decision drivers. A crucial model outcome was the secondary prediction of the size of the potential pool of goose hunters. We believe that POM is a beneficial framework for those wishing to define, test, and ultimately develop better predictive models of human decision-making and subsequent behaviors and feedbacks.

Hunter opinions on the management of migratory geese: a case of stakeholder involvement in adaptive harvest management

ABSTRACTKnowledge of hunter attitudes toward goose management is essential for the involvement of hunters in adaptive harvest management. Our study provides insight into processes of stakeholder involvement in adaptive harvest management, as demonstrated by the case of implementing the International Species Management Plan for the Svalbard-breeding pink-footed goose (Anser brachyrhynchus). We conducted an online survey among goose hunters in Norway in the main autumn staging area of this species, Nord-Trøndelag, which is also the area in which most geese are harvested nationally. Our results demonstrated that a majority of these hunters see themselves as active participants in management. These hunters expressed a willingness to support management objectives through the delivery of daily harvest reports and by complying with regulations, as defined by national wildlife authorities and the international management plan.

Impact of hunting along the migration corridor of pink‐footed geeseAnser brachyrhynchus– implications for sustainable harvest management

SummaryHunting can potentially affect population size, age composition, sex‐ratio, behaviour and distribution of natural populations, and understanding its impacts is a prerequisite to manage quarry species sustainably. Harvest management relies strongly on the existence of both strictly regulated hunting efforts and efficient monitoring of populations, their demography and harvest. These conditions are rarely met in practice.For the Svalbard‐breeding population of the pink‐footed gooseAnser brachyrhynchus, an internationally coordinated adaptive harvest management framework enables a flyway‐based assessment of harvest impact. Based on 25 years of population assessment and harvest data, we evaluate the differential impact of harvest along the migration corridor of the population.The analysis reveals that (i) total harvest and harvest rate (proportion of the population killed by hunting) have increased substantially in recent years, (ii) compared to adult geese, juveniles were overrepresented in the hunting bag by a factor of 3·7, (iii) the proportion of juveniles in the hunting bag differed between the two countries (Norway and Denmark) with an open season, and was more than twice as high in the former compared to the latter, and (iv) the increase in harvest rate seemed to be driven by increased hunting mortality of juvenile birds, with no clear impact on the growth rate of the population. However, this may partly relate to the transient dynamics and population inertia commonly seen in long‐lived species such as geese, and a 3‐year consecutive decline towards the end of our study period might be the first signs of an impending decline.Synthesis and applications. Our findings highlight that the impact of harvest varies along the migration corridor and between age classes of a single species and suggest that allocation of hunting effort in time and space is important to optimise harvest. Our example demonstrates the need for internationally coordinated, detailed population and harvest data which are essential for sustainable harvest management.

Regulation of the hunting season as a tool for adaptive harvest management — first results for pink‐footed geeseAnser brachyrhynchus

Adjustment of hunting season length is often used to regulate harvest of waterbirds but the effects are disputed. We describe the first results of season length extension on the harvest of the pink‐footed goose, which has been selected as the first test case of adaptive harvest management of waterbirds in Europe. In Denmark, the season (previously 1 September to 31 December) was extended to include January in 2014–2015 with the aim to increase the harvest and, in the longer term, reduce the population size. The total harvest in Denmark increased by 52% compared to previous years, and almost 50% of the Danish harvest was taken in the January extension. In the course of the hunting season, the proportion of adults in the bag increased. In this case, the outcomes from the first extension of season suggest that season length adjustment can be an effective tool to regulate harvest, though dependent on winter weather conditions and hunters' motivation for shooting geese.

Multilevel Learning in the Adaptive Management of Waterfowl Harvests: 20 Years and Counting

ABSTRACTIn 1995, the U.S. Fish and Wildlife Service implemented an adaptive harvest management program (AHM) for the sport harvest of midcontinent mallards (Anas platyrhynchos). The program has been successful in reducing long‐standing contentiousness in the regulatory process, while integrating science and policy in a coherent, rigorous, and transparent fashion. After 20 years, much has been learned about the relationship among waterfowl populations, their environment, and hunting regulations, with each increment of learning contributing to better management decisions. At the same time, however, much has been changing in the social, institutional, and environmental arenas that provide context for the AHM process. Declines in hunter numbers, competition from more pressing conservation issues, and global‐change processes are increasingly challenging waterfowl managers to faithfully reflect the needs and desires of stakeholders, to account for an increasing number of institutional constraints, and to (probabilistically) predict the consequences of regulatory policy in a changing environment. We review the lessons learned from the AHM process so far, and describe emerging challenges and ways in which they may be addressed. We conclude that the practice of AHM has greatly increased an awareness of the roles of social values, trade‐offs, and attitudes toward risk in regulatory decision‐making. Nevertheless, going forward the waterfowl management community will need to focus not only on the relationships among habitat, harvest, and waterfowl populations, but on the ways in which society values waterfowl and how those values can change over time. © 2015 The Authors. Wildlife Society Bulletin published by The Wildlife Society.

Exploring fall migratory patterns of American black ducks using eight decades of band-recovery data

As regions of habitat used by migratory waterfowl are subjected to rising anthropogenic pressures, establishing patterns of landscape use during migratory cycles is becoming increasingly important for managing and maintaining populations. Although data collection strategies such as global positioning system (GPS) telemetry promise high-resolution insight on geographic use of contemporary populations, decades of available band recovery records on many species can provide a low-cost, multi-generational alternative for defining broad, historically informed patterns of landscape use. We used nearly a century of band-recovery data to reconstruct patterns of fall migratory landscape use for American black ducks in the Mississippi and Atlantic flyways. We partitioned band recovery positions by month from September to February and spatially analyzed positions using kernel density estimates (KDEs) to delineate geographic regions used by American black ducks and track changes in landscape use during migration. Additionally, we considered the appropriateness of current management strategies, which treat American black ducks as a single population, by testing for differences in month-specific landscape use between ducks banded in the Mississippi and Atlantic flyways, and between international management units (ducks banded in Canada or the U.S.). We found that geographic distributions during peak migration faithfully recovered regions previously hypothesized as migratory corridors. Furthermore, regardless of banding origin, we found highly similar distributions and strong flyway fidelity in Atlantic flyway American black ducks. Conversely, American black ducks banded in the Mississippi flyway displayed differences in landscape use between Canadian and U.S. populations, with Canadian ducks significantly more likely to winter in areas within the Atlantic flyway (i.e., migrate between flyways). Flyway- and population-specific patterns of black duck landscape use indicate populations behave more independently than currently treated by management models (including the Adaptive Harvest Management plan), and that population maintenance may be advanced by managing stocks separately. © 2014 The Wildlife Society.

Conservation of wildlife populations: demography, genetics, and management

List of boxes. List of symbols. Preface. Acknowledgments. PART I: Background to applied population biology. 1. The Big Picture: Human population dynamics meets applied population biology. Introduction. Population ecology of humans. Extinction rates of other species. Humans and sustainable harvest. The big picture. Further reading. 2. Designing studies and interpreting population biology data: how do we know what we know?. Introduction. Obtaining reliable facts through sampling. Linking observed facts to ideasmind leads to understanding. Ethics and the wildlife population biologist. Summary. Further reading. 3. Genetic concepts and tools to support wildlife population biology. Introduction. What is genetic variation?. Genetic markers used in wildlife population biology. Insights into wildlife population biology using genetic tools. Summary. Further reading. 4. Estimating population vital rates. Estimating abundance and density. Survival estimation. Estimation of reproduction. Sex ratio. Summary. Further reading. PART II: POPULATION PROCESSES: THE BASIS FOR MANAGEMENT. 5. The simplest way to describe and project population growth: exponential and geometric change. Introduction. Fundamentals of geometric or exponential growth. Causes and consequences of variation in population growth. Quantifying population growth in a stochastic environment. Summary. Further reading. 6. Density dependent population change. Introduction. Negative density dependence. Positive density dependence. The logistic: one simple model of negative density-dependent population growth. Some counterintuitive dynamics: limit cycles and chaos. Summary. Further reading. 7. Accounting for age and sex-specific differences: population projection models. Introduction. Anatomy of a population-projection matrix. How timing of sampling affects the matrix. Projecting a matrix through time. Adding stochasticity to a matrix model. Sensitivity analysis. Case studies. Summary. Further reading. 8. Predation and wildlife populations. Does predation affect prey numbers?. Factors affecting how predation impacts prey numbers. Summary. Further reading. 9. Genetic Variation and Fitness of Wildlife Populations. Introduction. Long-term benefits of genetic variation. What determines levels of genetic variation in populations?. Quantifying the loss of heterozygosity: the inbreeding coefficient. When does inbreeding lead to inbreeding depression?. What to do when faced with inbreeding depression?. General Rules. Summary. Further reading. 10. Dynamics of Multiple Populations. Introduction. Connectivity among populations. Measuring connectivity among wildlife populations. Multiple populations are not all equal. Options for restoring connectivity. Summary. Further reading. PART III: APPLYING KNOWLEDGE OF POPULATION PROCESSES TO PROBLEMS OF DECLINING, SMALL, OR HARVESTABLE POPULATIONS. 11. Human Perturbations: Deterministic Factors Leading to Population Decline. Introduction. General effects of deterministic stressors on populations. Habitat loss and fragmentation. Introduced and invasive species. Pollution. Overharvest. Global climate change. Synergistic effects among deterministic stressors. Summary. Further reading. 12. Predicting the dynamics of small and declining populations. Introduction. Ecological characteristics predicting risk. The extinction vortex. Predicting risks in small populations. Population viability analysis: quantitative methods of assessing viability. Other approaches to assessing viability. Some closing thoughts about assessing viability. Summary. Further reading. 13. Bridging applied population and ecosystem ecology with focal species concepts. Introduction. Flagship species. Umbrella species. Indicator species. Keystone species and strong interactors. Summary. Further reading. 14. Population biology of harvested populations. Introduction. Effects of hunting on population dynamics. Long term effects: hunting as a selective force. Models to guide sustainable harvests. Waterfowl harvest and adaptive harvest management. Management of overabundant and pest populations. Summary. Further reading. Epilogue. References. Species lists. Subject index.

Band reporting probabilities for mallards recovered in the United States and Canada

Reliable estimates of annual harvest rates are required for the implementation of mallard (Anas platyrhynchos) adaptive harvest management decision frameworks. Because not all standard bands recovered during the hunting season are reported, band reporting probabilities are needed to estimate mallard harvest rates. Information from birds recovered with bands that notify finders of a reward (i.e., reward bands) can be used to estimate band reporting rates. We analyzed reward banding data for 3 stocks of mallards to estimate reporting probabilities that can be used to estimate harvest rates for birds recovered with toll-free or web-address bands. Specifically, we explored spatial variability in reporting probabilities, and assessed whether reporting probabilities varied among years. Our analysis indicated that reporting probabilities varied among the 4 Flyways, eastern Canada, and western Canada and Alaska. We had difficulty interpreting temporal fluctuations and found little evidence for any meaningful trends in reporting rates between 2002 and 2010. We recommend that reporting probabilities of 0.67 in the Atlantic Flyway, 0.81 in the Mississippi Flyway, 0.70 in the Central Flyway, 0.76 in the Pacific Flyway, 0.50 in eastern Canada, and 0.57 in western Canada and Alaska be used to estimate harvest probabilities for birds recovered in these regions. © 2013 The Wildlife Society.

Harvest and dynamics of duck populations

AbstractThe role of harvest in the dynamics of waterfowl populations continues to be debated among scientists and managers. Our perception is that interested members of the public and some managers believe that harvest influences North American duck populations based on calls for more conservative harvest regulations. A recent review of harvest and population dynamics of North American mallard (Anas platyrhynchos) populations (Pöysä et al. 2004) reached similar conclusions. Because of the importance of this issue, we reviewed the evidence for an impact of harvest on duck populations. Our understanding of the effects of harvest is limited because harvest effects are typically confounded with those of population density; regulations are typically most liberal when populations are greatest. This problem also exists in the current Adaptive Harvest Management Program (Conn and Kendall 2004). Consequently, even where harvest appears additive to other mortality, this may be an artifact of ignoring effects of population density. Overall, we found no compelling evidence for strong additive effects of harvest on survival in duck populations that could not be explained by other factors. © 2012 The Wildlife Society.

Distribution and derivation of white‐winged dove harvests in Texas

AbstractBand recoveries provide requisite data for evaluating the spatial distribution of harvest relative to the distribution of breeding stocks for a wide variety of migratory species. We used direct and indirect band‐recovery data to evaluate the distribution and derivation of harvest of white‐winged doves (Zenaida asiatica) banded before hunting season in 3 distinct strata in Texas, USA, during 2007–2010. We banded 60,742 white‐winged doves during 2007–2010, and based on 2,458 harvest recoveries, the majority (&gt;95%) of white‐winged dove harvest occurred during the first 2 months of the hunting season (Sep–Oct). Juvenile white‐winged doves represented a greater percentage of the direct recoveries than adults across all strata (north = 80%, central = 69%, south = 82%) and the majority of direct band recoveries (north = 75%, central = 90%, south = 78%) occurred within the original banding strata. Age‐specific weighting factors and harvest derivation indicated that both juvenile and adult harvest were highest within the strata of original banding. Harvest distribution data corrected for band‐reporting rates indicated high fidelity of white‐winged doves to specific geographic strata, with little interplay between strata. Our results suggest that population vital‐rate estimates for survival and harvest for use in future Adaptive Harvest Management should focus on stock‐specific levels. © 2012 The Wildlife Society.

Spinning‐wing decoy use and reported duck harvest in Illinois: Implications for adaptive harvest management

AbstractUse of battery‐powered spinning‐wing decoys (SWDs) by duck hunters has generated questions as to the effect these decoys may have on duck harvests. I used data from the annual Illinois Waterfowl Hunter Survey for duck hunting seasons 1999 through 2003 to compare mallard (Anas platyrhynchos) and total duck harvest, reported days afield, and duck crippling rates between hunters using and not using SWDs. For the each of the 5 years reported, mean mallard harvest was greater among hunters using SWDs than among hunters not using the decoys and effect size was substantial (1999: F = 355.01, P &lt; 0.001; 2000: F = 567.92, P &lt; 0.001; 2001: F = 333.25, P &lt; 0.001; 2002: F = 321.58, P &lt; 0.001; 2003: F = 299.00, P &lt; 0.001). Mean reported total ducks harvested was greater for decoy users than non‐users, and I found effect sizes to be substantial for all years (1999: F = 301.80, P &lt; 0.001; 2000: F = 607.76, P &lt; 0.001; 2001: F = 369.49, P &lt; 0.001; 2002: F = 321.59, P &lt; 0.001; 2003: F = 335.82, P &lt; 0.001). Decoy users reported hunting more days than non‐users (1999: F = 71.00, P &lt; 0.001; 2000: F = 716.50, P &lt; 0.001; 2001: F = 486.75, P &lt; 0.001; 2002: F = 410.72, P &lt; 0.001; 2003: F = 466.09, P &lt; 0.001). I observed substantial effect size for days hunted by decoy use for each year except for 1999–2000, for which effect size was typical. Hunters using SWDs reported greater crippled ducks than for hunters not using the decoys, with typical effect sizes observed for each year I examined (1999: F = 168.42, P &lt; 0.001; 2000: F = 361.34, P &lt; 0.001; 2001: F = 163.05, P &lt; 0.001; 2002: F = 153.29, P &lt; 0.001; 2003: F = 169.18, P &lt; 0.001). I did not observe significant relationships between years of hunting experience and decoy use (R2 range = 0.051–0.071). My findings support claims that SWDs lead to increased duck harvests. Recent actions by some state wildlife management agencies have resulted in a mixed approach toward regulating use of SWDs, ranging from prohibiting their use to removing all restrictions. This study seeks to provide managers with greater understanding of potential impacts of SWD use on waterfowl harvests. © 2011 The Wildlife Society.

Effects of harvest and climate on population dynamics of northern bobwhites in south Florida

Context Hunting-related (hereafter harvest) mortality is assumed to be compensatory in many exploited species. However, when harvest mortality is additive, hunting can lead to population declines, especially on public land where hunting pressure can be intense. Recent studies indicate that excessive hunting may have contributed to the decline of a northern bobwhite (Colinus virginianus) population in south Florida. Aims This study aimed to estimate population growth rates to determine potential and actual contribution of vital rates to annual changes in population growth rates, and to evaluate the role of harvest and climatic variables on bobwhite population decline. Methods We used demographic parameters estimated from a six-year study to parameterise population matrix models and conduct prospective and retrospective perturbation analyses. Key results The stochastic population growth rate (λS = 0.144) was proportionally more sensitive to adult winter survival and survival of fledglings, nests and broods from first nesting attempts; the same variables were primarily responsible for annual changes in population growth rate. Demographic parameters associated with second nesting attempts made virtually no contribution to population growth rate. All harvest scenarios consistently revealed a substantial impact of harvest on bobwhite population dynamics. If the lowest harvest level recorded in the study period (i.e. 0.08 birds harvested per day per km2 in 2008) was applied, λS would increase by 32.1%. Winter temperatures and precipitation negatively affected winter survival, and precipitation acted synergistically with harvest in affecting winter survival. Conclusions Our results suggest that reduction in winter survival due to overharvest has been an important cause of the decline in our study population, but that climatic factors might have also played a role. Thus, for management actions to be effective, assessing the contribution of primary (e.g. harvesting) but also secondary factors (e.g. climate) to population decline may be necessary. Implications Reducing hunting pressure would be necessary for the recovery of the bobwhite population at our study site. In addition, an adaptive harvest management strategy that considers weather conditions in setting harvest quota would help reverse the population decline further.

Learning and adaptation in the management of waterfowl harvests

A formal framework for the adaptive management of waterfowl harvests was adopted by the U.S. Fish and Wildlife Service in 1995. The process admits competing models of waterfowl population dynamics and harvest impacts, and relies on model averaging to compute optimal strategies for regulating harvest. Model weights, reflecting the relative ability of the alternative models to predict changes in population size, are used in the model averaging and are updated each year based on a comparison of model predictions and observations of population size. Since its inception the adaptive harvest program has focused principally on mallards ( Anas platyrhynchos), which constitute a large portion of the U.S. waterfowl harvest. Four competing models, derived from a combination of two survival and two reproductive hypotheses, were originally assigned equal weights. In the last year of available information (2007), model weights favored the weakly density-dependent reproductive hypothesis over the strongly density-dependent one, and the additive mortality hypothesis over the compensatory one. The change in model weights led to a more conservative harvesting policy than what was in effect in the early years of the program. Adaptive harvest management has been successful in many ways, but nonetheless has exposed the difficulties in defining management objectives, in predicting and regulating harvests, and in coping with the tradeoffs inherent in managing multiple waterfowl stocks exposed to a common harvest. The key challenge now facing managers is whether adaptive harvest management as an institution can be sufficiently adaptive, and whether the knowledge and experience gained from the process can be reflected in higher-level policy decisions.

Understanding changes in bird populations – the role of bird marking

Studies of marked birds play a central role in research on avian population dynamics and life histories because they are the main means of estimating survival, recruitment and dispersal. Integrated Population Monitoring aims to combine such information from ringing with data on abundance, productivity and the environment in order to develop population models that address applied questions. Diagnosing the demographic and environmental causes of population declines provides a basis for developing management prescriptions for population recovery. We discuss examples of how such studies are contributing to the conservation of European farmland birds and to understanding declines in Afro–Palaearctic migrants. Adaptive harvest management of North American duck populations demonstrates that similar principles apply to the management of quarry species. Over the next two decades we expect significant advances in our understanding of seasonal variation in demographic rates, of density dependence and of the ways in which continental‐scale population dynamics are built up from processes operating at much smaller spatial scales. This will be achieved through analyses of large‐scale data sets, the combination of conventional and new technologies and the widespread application of fully integrated modelling methods. Large‐scale data gathering through national ringing centres will play a key part in this process.