Wintering lesser scaup spatial distribution and behavioral energetics in the Chesapeake Bay
Date
2024
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Publisher
University of Delaware
Abstract
Over the past two decades, Lesser Scaup (Aythya affinis) populations have been declining, bringing focus to understanding scaup non-breeding and wintering requirements. The Chesapeake Bay is an important wintering area that provides ample food resources and a constant source of open water habitat. Continuous landscape changes around the Chesapeake Bay may have altered the type, quantity, and distribution of food resources available thus impacting their habitat use and populations. Past research on scaup foraging ecology in this region has been restricted to diet analyses from hunter-harvested birds and behavioral data collected from observational scan sampling. I sought to expand our knowledge of the foraging ecology of scaup by monitoring the movements and behaviors of 29 Lesser Scaup marked with GPS/GSM transmitters wintering in the Chesapeake Bay between the winters of 2021–2023. I calculated monthly home ranges using autocorrelated kernel density estimates and performed a GLMM to compare home range sizes to year and month, and individual sex and age. I found that home range sizes were not significantly different between any of the predictor variables. Coupling location and behavior data collected from tri-axial accelerometer (ACC) data from the GPS/GSM transmitters, I found the top-ranking model for foraging locations indicated that scaup selected for locations that were closer to shore but away from anthropogenic surfaces in the water, higher tide levels, and used sandy and biogenetic hard bottom substrates. Using diurnal instantaneous scan sampling and ACC behavior data I calculated a 24-hr daily energy expenditure estimate of wintering Lesser Scaup and found that using the diurnal scanning observations produced a significantly lower estimate than the estimate calculated by the 24-hr ACC data. I compared the behavior proportions from the ACC data of the two most energetically demanding behaviors (feeding and flying) between diurnal and nocturnal time periods. Both a Wilcoxon rank-sums test and a binomial GLMM showed that feeding occurred 42% more during the day than the night and flight occurred 23% more in the night than the day. A binomial GLMM also revealed that there was significantly more feeding and less flight of birds in the ACC data than in the visual scanning data.
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Keywords
Aythya affinis, Accelerometer, Chesapeake Bay, Behavioral energetics