Determining food use and time/energy budgets of wintering and staging Atlantic brant

Graduate Research Assistants: Zach Ladin (M.S. Wildlife Ecology)

Collaborators: Paul Castelli (New Jersey Division of Fish and Wildlife), Atlantic Flyway Council Migratory Gamebird Technical Section, University of Delaware College of Agriculture and Natural Resources, New Jersey Division of Fish and Wildlife, U.S. Fish and Wildlife Service, Forsythe and Cape May National Wildlife Refuges.

Atlantic brant (Branta bernicla hrota) populations and preferred foods (e.g. Submerged Aquatic Vegetation [SAV]) have experienced long-term variability or decline. The current 2-year study was initiated in 2006 to build a bioenergetics model for use in evaluating habitat nutritional supply and demand across their winter range. A bioenergetics approach is valuable as a planning tool to identify the amount of foraging habitat required to meet the North American Waterfowl Management Plan’s population objectives and help identify areas for priority action. As a first step to building a bioenergetics model, we began an effort to quantify winter time/energy budgets for brant across a variety of meso-scale and macro-scale sites. Specifically our goals are: 1) Determine the amount of time brant dedicate to different behavioral states to estimate hourly energy expenditure. In addition, we must know how the percentage of time spent in those behaviors varies with habitat type, weather, disturbance, and time of year. 2) Determine the feeding rate and foods ingested in different habitat types and time of year. This will help determine how much ingestion of the plants is required for metabolic function of different behavioral states. 3) Collect the contents of the upper gastrointestinal tracts of brant through temporally and spatially explicit carcass collections to determine which plants are selected by brant and how these vary with habitat type and time of year. We will also determine caloric content of GI tract contents. 4) Collect brant foods to determine the caloric availability in a variety of habitat types throughout the winter. 5) Determine seasonal dietary trends through stable isotope analysis of food items, foregut contents and leg and liver tissues. To meet the objectives of this research we conducted our first year field work in ten 225km2 study areas (macroplots) distributed throughout their wintering range (1 plot in Rhode Island, 2 plots in Connecticut, 2 plots on Long Island, New York, 3 plots in New Jersey, 1 plot in Maryland, and 1 plot in Virginia). All sites had a mixture of upland habitat, salt marsh, and estuarine habitat composed of SAV (Ulva, eelgrass etc.). One study area in Delaware was added for the 2007-08 field season.

Photo credit: Zach Ladin