To facilitate decisions to classify species according to risk of extinction, we used Bayesian methods to analyze trend data for the Spectacled Eider, an arctic sea duck. Trend data from three independent surveys of the Yukon‐Kuskokwim Delta were analyzed individually and in combination to yield posterior distributions for population growth rates. We used classification criteria developed by the recovery team for Spectacled Eiders that seek to equalize errors of under‐ or overprotecting the species. We conducted both a Bayesian decision analysis and a frequentist (classical statistical inference) decision analysis. Bayesian decision analyses are computationally easier, yield basically the same results, and yield results that are easier to explain to nonscientists. With the exception of the aerial survey analysis of the 10 most recent years, both Bayesian and frequentist methods indicated that an endangered classification is warranted. The discrepancy between surveys warrants further research. Although the trend data are abundance indices, we used a preliminary estimate of absolute abundance to demonstrate how to calculate extinction distributions using the joint probability distributions for population growth rate and variance in growth rate generated by the Bayesian analysis. Recent apparent increases in abundance highlight the need for models that apply to declining and then recovering species.
Severe declines of waterfowl populations on the Yukon–Kuskokwim Delta (YKD), Alaska, from the 1960s through the mid-1980s, prompted the initiation in 1985 of standardized surveys of the region’s breeding birds. These entailed coordinated annual aerial and ground-based surveys, tiered by area and intensity of coverage, which have provided data for this area critical to waterfowl production. Aerial surveys were used to provide broad-scale indices of breeding pairs and the total bird population along the YKD’s entire coast, while ground surveys provided finer-scale estimates of breeding chronology, egg production, nesting effort, habitat use, and predation within core breeding habitats. The extensive coverage of the aerial surveys also provided objective data for expansion of the ground-based sampling, while the nest surveys contributed to a better understanding of aerial survey data, including indices of detection rates. Here we describe patterns of long-term population growth of the Cackling Goose (Branta hutchinsii minima), Greater White-fronted Goose (Anser albifrons frontalis), and Emperor Goose (Chen canagica) relative to population objectives for the Pacific Flyway. We also describe significant growth in the western Alaska population of the Spectacled Eider (Somateria fischeri) following the species’ listing as threatened under the Endangered Species Act in 1993. Growth rates of population indices were positive for the four species from 1985 to 2014, but rates varied within this interval. We found no evidence that dates of nest initiation and hatching advanced significantly between 1985 and 2014. The proportion of waterfowl recorded as pairs by aerial survey crews was correlated with the surveys’ start date for geese but not for the Spectacled Eider. The ratio of nests to aerially observed pairs was 4.8 for Cackling Geese, 5.2 for Greater White-fronted Geese, 5.4 for Emperor Geese, and 2.4 for Spectacled Eiders. The nest-to-pair ratio is one tool by which indices based on aerial surveys can be converted to an estimate of the number of breeding pairs. Together these aerial and ground-based surveys provide the information needed to implement waterfowl management and recovery plans, assess waterfowl distribution across the YKD, measure nesting chronology relative to changes in climate, develop indices to detection rate in aerial surveys, and assess waterfowl vulnerability.
Spectacled eider (Somareria jischeri) populations in western Alaska are now less than 4% of the numbers estimated in the early 1970s. In 1992, an estimated 1721 nesting pairs remained on the Yukon-Kuskokwim Delta. Causes of this rapid and continuing decline of-14% per year are undocumented. Many aspects of spectacled eider biology remain unknown, including their marine foraging habitats, food items, migratory movements, and population ecology. A review of some biological characteristics and possible threats to the species suggests the importance of quantifying potential impacts from parasites and disease, subsistence harvest, predation during brood rearing, and alteration of Bering Sea food resources. Factors causing the population decline of spectacled eiders must be determined and appropriate actions taken to reverse the trend.
Rapid physical changes that are occurring in the Arctic are primary drivers of landscape change and thus may drive population dynamics of Arctic-breeding birds. Despite the importance of this region to breeding and molting waterbirds, lack of a comprehensive analysis of historic data has hindered quantifying avian population change. We estimated distribution, abundance, and spatially explicit population trend of 20 breeding waterbird species using 25 years (1992-2016) of aerial survey data collected on the Arctic Coastal Plain (ACP), Alaska. The ACP is an extensive wetland complex on Alaska's North Slope that supports millions of breeding waterbirds and includes portions of the National Petroleum Reserve-Alaska and the Arctic National Wildlife Refuge. We summarized annual counts into approximately 6-km by 6-km grid cells and analyzed data with generalized linear mixed models that accounted for survey timing and spatio-temporal autocorrelation. Geese and swans were most abundant along the coast between Admiralty Bay and Prudhoe Bay. Sea ducks, generalist predators (i.e., jaeger, gulls, terns), and loons were most abundant between Utqiaġvik and Point Lay, Alaska. Important areas for most species included the coastal fringe near Teshekpuk Lake, the Colville River Delta, and Admiralty Bay. The National Petroleum Reserve-Alaska was an important area for all species examined. Conversely, density on the coastal plain of the Arctic National Wildlife Refuge was greater than average for 20% of species. Annual population growth rates over the 25-year survey period were variable: 13 increased (range: 1.4%-13.8%), one decreased (-3.4%), and six were stable. However, even species with no overall population trend had areas of changing population size, suggesting localized conditions affected waterbird distributions on the ACP. Our results can be used to better inform land use decisions, improve monitoring of waterbird populations, and increase understanding of avian response to ecological change in the Arctic. Changements spatio-temporels chez des populations d'oiseaux aquatiques nichant dans la Plaine côtière arctique de l'Alaska RÉSUMÉ. Les changements physiques rapides qui se produisent dans l'Arctique figurent parmi les premiers facteurs responsables des changements qui surviennent dans le paysage, et pourraient donc déterminer la dynamique des populations d'oiseaux nichant dans l'Arctique. Malgré l'importance de cette région pour la nidification et la mue des oiseaux aquatiques, l'absence d'une analyse complète des données historiques a freiné la quantification des changements advenus dans les populations d'oiseaux. Nous avons estimé la répartition, l'abondance et la tendance des populations de façon explicite spatialement chez 20 espèces d'oiseaux aquatiques au moyen de 25 années (1992-2016) de données issues de relevés aériens menés sur la Plaine côtière arctique (PCA), en Alaska. La PCA est un vaste complexe de milieux humides dans la région de North Slope en Alaska et supporte des millions d'oiseaux aquatiques nicheurs...
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