Spectacled eiders were listed as Threatened under the ESA in 1993 primarily due to a 96% population decline on the Yukon-Kuskokwim Delta in Alaska (YKD), one of three breeding areas worldwide. The Spectacled Eider Recovery Plan ties recovery criteria to numbers of breeding pairs in each of the three nesting areas (YKD, North Slope, Arctic Russia). Lewis et al. (2019) compared ground-based nest abundance estimates to aerially estimated indicated breeding pairs to provide a means to assess recovery status from detection corrected aerial surveys. He reported that aerial crews detect 30-70% of nesting eider pairs, depending on nesting density; however, nest population estimates used in that study were derived from a nest detection model developed nearly 30 years ago that do not reflect the detection functions of annual ground-based crews. In the current study we will use distance sampling to estimate nest detection. This method can be implemented each year and will yield population estimates corrected for year-specific observers and environmental conditions; thus, leading to more precise and potentially less biased population estimates. The application of nest density estimates for measuring aerial detection rate extends beyond spectacled eiders to other waterfowl species of conservation concern including minima cackling geese, emperor geese, and Pacific brant. The objectives of this project are to estimate the population of spectacled eider, common eider, and goose nests, in the YKD ‘core nesting area’; estimate a detection function for each species; determine effort (number of transects) required to obtain a given estimate of precision.
