Date of Award
Master of Science in Biological and Environmental Sciences (MSBES)
Scott R. McWilliams
Young forests and the wildlife that are dependent upon them are uncommon and declining within the Northeastern U.S. As such, forest management plans have been implemented to create and maintain young forest for wildlife, including migratory birds such as the American Woodcock (Scolopax minor) that use young forest to meet their life history needs. Given that most Northeastern woodcock migrate between more northerly breeding areas and southern wintering areas, information about how post-breeding habitat quality and body composition carry over to influence fall migration strategies and residency is important for their management but currently unknown. I investigated how habitat quality prior to fall migration influenced the timing of departure, departure body composition and subsequent migratory phenology of the American Woodcock. First, I validated the non-destructive deuterium dilution method for estimating body composition of woodcock prior to departure in fall and used these models to estimate the rate of fattening for free-living fall-staging woodcock in Rhode Island (Chapter 1). Second, I assessed the influence of post-breeding habitat quality on departure body composition and fall migration patterns in a southern New England breeding population of American Woodcock (Chapter 2).
In Chapter 1, I report the first validation of the deuterium-dilution method for estimating the body composition of a fall staging shorebird. I captured male (n = 35) and female (n = 13) woodcock in the fall of 2018 and 2019 (September – November), directly measured the body composition of 20 woodcock and used predictive models to estimate the body composition of fall-staging 28 woodcock which were released to continue on fall migration. I directly measured for each wild-caught woodcock (n = 20) their total body water, age, body mass, and fat score, and then used multiple regression and measured whole-body water and body composition to estimate the whole-body lean mass and fat mass of woodcock with relative errors of 1.37% and 11.26 % for the wet lean mass and fat mass, respectively. Estimates of body composition using only morphometrics such as fat score were poor predictors of body composition. I used the estimated fat at capture to assess the rate of fattening in freeliving fall staging woodcock (n = 28) in southern New England. On average, woodcock initiated fat deposition on September 22, and deposited fat at a rate of 0.42 ± 0.09 g fat per day-1. Our results suggest that the deuterium dilution method offers a reliable, accurate and non-destructive method to estimate the body composition of woodcock during the fall. This information can be used by managers as an effective tool to assess how habitat management affects body composition dynamics at staging and stopover sites used by woodcock.
In a complimentary study (Chapter 2), I used VHF and satellite telemetry to track woodcock prior to and during fall migration and quantified the pre-migratory habitat quality and departure body composition for fall migrating woodcock. Woodcock that overwintered within Rhode Island had lower fat upon capture, as well as used lower quality habitat during the fall than woodcock that migrated. Woodcock migrated after reaching a threshold of 27 g of fat. Woodcock that departed earlier were long-distance migrants that had inhabited higher quality landscapes prior to migration, stored less fat upon departure, migrated faster, used more stopovers during migration, and migrated to more southern wintering areas. In contrast, woodcock that departed later were short-distance migrants that had inhabited lower quality landscapes prior to migration yet stored more fat upon departure, used fewer stopovers during migration, and migrated to more northerly wintering areas. During migration, woodcock used on average 1.07 ± 0.26 stopovers in Virginia, North Carolina, Maryland, Delaware, New Jersey, Connecticut, New York, South Carolina and Georgia, and migrated 1149.18 ± 105.57 km along the Atlantic Coastal Plain to wintering grounds distributed from Maryland to Alabama. I found that woodcock that breed in southern New England are obligate partial migrants that include residents, and shorter- and longer-distance migrants. Given the anticipated effects of climate change and urbanization on partial migration strategies, the proportion of residents overwintering in Rhode Island or using short-distance migratory strategies may increase, and as such these overwintering areas deserve conservation and management attention.
Graham, Clayton Lee, "THE INFLUENCE OF PRE-MIGRATORY BODY COMPOSITION AND HABITAT QUALITY ON FALL MIGRATION IN THE AMERICAN WOODCOCK (SCOLOPAX MINOR)" (2020). Open Access Master's Theses. Paper 1882.