James A. Dubovsky

Potential Reproductive Consequences of Winter-Diet Restriction in Mallards

Food restriction during winter may subsequently affect waterfowl reproduction. Therefore, we tested the effects of restricted and ad libitum (control) food availability during winter 1987-88 on reproductive performance of captive wild-strain and game-farm female mallards (Anas platyrhynchos) in Mississippi. Females fed restricted diets weighed less (P 0.05) between females fed restricted diets and those fed ad libitum. Few wild-strain females renested, but clutch sizes of game-farm females declined (P < 0.01) after initial nests. Simulation modeling revealed that recruitment rates (i.e., n F/breeding F) may decrease 3-15% if free-ranging mallards were to experience nesting delays of 1-3 weeks. We hypothesize that poor feeding conditions during winter could negatively affect mallard recruitment primarily through delayed nesting, but replication of our study with wild-strain ducks and other experimental design considerations is recommended. J. WILDL. MANAGE. 58(4):780-786

Modeling Spatial Variation in Waterfowl Band-Recovery Data

Historically, the statistical complexity of modeling spatial relationships in band-recovery data has limited the use of spatial models in the management of waterfowl populations. Consequently, managers have assumed simplified spatial relationships (e.g., by stratification and pooling data over large geographic areas) to obtain spatially explicit estimates of vital rates. As an alternative, we used a binomial random effects approach to modeling spatial variation in band-recovery data. The model accommodates spatial correlation and heterogeneity in recovery rates and facilitates spatially explicit estimation of recovery rates with sparse data and at arbitrary levels of spatial resolution. Although the model is structurally simple, estimation using conventional likelihood techniques is complex. Instead, we rely on a technique known as Markov chain Monte Carlo (MCMC) simulation. We used this model to construct a map of mallard (Anas platyrhynchos) recovery rates on a relatively fine-grained grid and for estimation of recovery rates within predefined geographic strata. The results show a strong gradient in recovery rate, with lower values in the western United States and higher values in the eastern United States. The spatial correlation in the model allows useful stratum-level estimates to be produced for strata with small sample sizes.

Continental Survival and Recovery Rates of Northern Pintails Using Band- Recovery Data

Abstract Unlike other North American prairie-nesting dabbling ducks, northern pintail (Anas acuta) populations have not increased since the early 1990s and remain well below the long-term average for traditional survey areas. Previously reported estimates of annual survival and recovery rates for pintails did not investigate any spatial or temporal factors to explain annual variation of these rates. We used band-recovery data from 1970 to 2003 to test the influence of temporal periods defined by differing harvest regulations and habitat conditions of breeding grounds with spatially delineated regions on survival and recovery rates of northern pintails in North America. We separated regions based on a multiresponse permutation procedure to identify banding blocks with dissimilar recovery distributions based on a cluster analysis. We categorized time by grouping years into temporal periods based on bag limits, season lengths, or overflight versus nonoverflight years. We used the Brownie approach in Program MARK to evaluate 46 a priori models estimating survival and recovery rates. The best approximating model indicated that survival varied with age, sex, and region with additive time and interactive time-by-age and time-by-region effects. Recovery rate was best represented by a fully interactive term comprised of age, sex, region, and year. There were no statistical differences among average annual survival point estimates between age and sex classes within each region, and our estimates were similar to previous unpublished studies. We found the eastern region had decreased survival and increased recovery rates compared to other regions. Trends in pintail survival suggest that variation in annual survival was not the cause of the initial decrease in the northern pintail population and is unlikely the dominant factor preventing the population from increasing. The influence of other population parameters, such as recruitment rate, should be investigated to further evaluate other causes for the population status of northern pintails. Use of the top-ranked model to estimate annual survival and recovery rates for northern pintails in North America, which indicated that annually varying estimates of survival rates were better supported by the data than grouping years into temporal classes (i.e., based on bag limits, season lengths, and overflight yr) can be used by managers and policy makers when considering annual harvest regulations and effects of conservation efforts. Managers should incorporate these estimates into future demographic studies of pintails as well as consider using the top-ranked model for future analyses of band-recovery data.

Optimal population prediction of sandhill crane recruitment based on climate‐mediated habitat limitations

1. Prediction is fundamental to scientific enquiry and application; however, ecologists tend to favour explanatory modelling. We discuss a predictive modelling framework to evaluate ecological hypotheses and to explore novel/unobserved environmental scenarios to assist conservation and management decision-makers. We apply this framework to develop an optimal predictive model for juvenile (<1 year old) sandhill crane Grus canadensis recruitment of the Rocky Mountain Population (RMP). We consider spatial climate predictors motivated by hypotheses of how drought across multiple time-scales and spring/summer weather affects recruitment. 2. Our predictive modelling framework focuses on developing a single model that includes all relevant predictor variables, regardless of collinearity. This model is then optimized for prediction by controlling model complexity using a data-driven approach that marginalizes or removes irrelevant predictors from the model. Specifically, we highlight two approaches of statistical regularization, Bayesian least absolute shrinkage and selection operator (LASSO) and ridge regression. 3. Our optimal predictive Bayesian LASSO and ridge regression models were similar and on average 37% superior in predictive accuracy to an explanatory modelling approach. Our predictive models confirmed a priori hypotheses that drought and cold summers negatively affect juvenile recruitment in the RMP. The effects of long-term drought can be alleviated by short-term wet spring-summer months; however, the alleviation of long-term drought has a much greater positive effect on juvenile recruitment. The number of freezing days and snowpack during the summer months can also negatively affect recruitment, while spring snowpack has a positive effect. 4. Breeding habitat, mediated through climate, is a limiting factor on population growth of sandhill cranes in the RMP, which could become more limiting with a changing climate (i.e. increased drought). These effects are likely not unique to cranes. The alteration of hydrological patterns and water levels by drought may impact many migratory, wetland nesting birds in the Rocky Mountains and beyond. 5. Generalizable predictive models (trained by out-of-sample fit and based on ecological hypotheses) are needed by conservation and management decision-makers. Statistical regularization improves predictions and provides a general framework for fitting models with a large number of predictors, even those with collinearity, to simultaneously identify an optimal predictive model while conducting rigorous Bayesian model selection. Our framework is important for understanding population dynamics under a changing climate and has direct applications for making harvest and habitat management decisions.

Replacement Cost Valuation of Northern Pintail (Anas acuta) Subsistence Harvest in Arctic and Sub-Arctic North America

Migratory species provide economically beneficial ecosystem services to people throughout their range, yet often, information is lacking about the magnitude and spatial distribution of these benefits at regional scales. We conducted a case study for Northern Pintails (hereafter pintail) in which we quantified regional and sub-regional economic values of subsistence harvest to indigenous communities in Arctic and sub-Arctic North America. As a first step, we used the replacement cost method to quantify the cost of replacing pintail subsistence harvest with the most similar commercially available protein (chicken). For an estimated annual subsistence harvest of ˜15,000 pintail, our mean estimate of the total replacement cost was ˜

Do economic values and expenditures for viewing waterfowl in the U.S. differ among species

63,000 yr−1 (

Willingness to Pay for Conservation of Transborder Migratory Species: A Case Study of the Mexican Free-Tailed Bat in the United States and Mexico

2010 USD), with sub-regional values ranging from

Ecosystem service flows from a migratory species: Spatial subsidies of the northern pintail.

263 yr−1 to

Uncertainty and the management of mallard harvests

21,930 yr−1. Our results provide an order-of-magnitude, conservative estimate of one component of the regional ecosystem-service values of pintails, providing perspective on how spatially explicit values can inform migratory species conservation.

Conditions and Limitations on Learning in the Adaptive Management of Mallard Harvests

ABSTRACT Many economic studies value birdwatching in general and often do not account for potential differences in viewers’ benefits from observing different species. But, how different are economic values of viewing various bird species? To answer that question, we surveyed Ducks Unlimited (DU) members using an online questionnaire to estimate trip expenditures and consumer surplus per trip for viewing pintail ducks, waterfowl in general, and other species of waterfowl. Expenditures per trip were USD