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Breeding Ecology of the American Black Duck (Anas rubripes) on Bloodsworth, South Marsh, and Smith Islands, Chesapeake Bay

Michael Haramis, Dennis Jorde, Glenn Olsen, and Dan Stotts – U.S. Geological Survey, Biological Resources Division, Patuxent Wildlife Research Center, Laurel, Maryland 20708–4015

Michael Harrison, Martin National Wildlife Refuge, Smith Island, Ewell, Maryland 21824

Joe Hautzenroder, Navy Facilities Engineering Command, Washington Navy Yard, Washington, D.C. 20374–5018

Abstract:

An initiative by the Department of Defense – Navy to include its 5,400 acre Bloodsworth Island Shore and Bombardment Range under cooperative management by the North American Waterfowl Management Plan has resulted in our participation to conduct research on the breeding ecology of the American black duck (Anas rubripes) in the Bloodsworth archipelago. This series of 3 large, offshore islands remains some of the most valuable wild lands and wildlife habitat in the Chesapeake Bay, and is one of the last remaining strongholds for breeding black ducks in the region.

Because of live ordinance on Bloodsworth Island, comparative study of insular breeding black ducks was conducted in 1995 and 1996 on Martin National Wildlife Refuge, Smith Island. We marked 56 females and 10 male black ducks over the course of the study with 20 gm implant radio transmitters. Individuals were tracked throughout the breeding season to locate nests and to determine nest fate, period survival, and habitat use of broods. A pilot study investigating movements of red foxes (Vulpes vulpes) was initiated in 1996 and GIS mapping of the island was completed through support from the University of Maryland. In addition, a 12–year summary and analysis of black duck and mallard (Anas platyrhynchos) bandings in the region was completed.

Our findings suggest that island saltmarsh habitats present a harsh economy for black ducks. We base this conclusion on an overall weak nesting effort (i.e., low frequency of nesting, poor renesting), and poor hatching success due to excessive predation and vulnerability of nests to storm tides. In addition, the virtual absence of freshwater in an environment where tide water ranges from 12–15 ppt, suggests some cost in growth and survival of ducklings. Finally, the extent and quality of near–shore littoral submerged aquatic vegetation, especially widgeon grass (Ruppia maritima), is a critical food resource to island inhabiting black ducks. Declines in widgeongrass meadows have likely had a far reaching negative effect on black ducks throughout the Chesapeake Bay. As a likely response to escape predation by excessively high gull populations and by red foxes, black ducks are selecting submarginal low needlerush marsh for nesting in lieu of upland sites. Management efforts to mediate these sources of predation will likely have the greatest immediate benefit for island nesting black ducks.

 

Our close association with watermen gave us unique historical and current cultural knowledge of Smith Island.

Smith Island is a complex marsh habitat of tidal guts and ponds composed of nearly 80% needlerush and only a few upland tree hummocks.

Implant radio transmitters (left) were surgically placed in the abdomen of black ducks by veterinarian Dr. Glenn Olsen (right).

Dr. Glenn Olsen inspecting a post–surgery black duck before release.

Radio–marked black ducks were tracked from ground stations shown above, and also from aircraft and boats.

Juxtaposition of tidal ponds and creeks and near–shore littoral of widgeongrass meadows provided the best island habitat for black ducks.

Black ducks selected needlerush marsh almost exclusively for nesting. Such nests were large structures 25 – 30 cm high to avoid flooding from tides.

Few mortalities were recorded. This skeleton was all that remained after our radio–marked black duck fell prey to a peregrine falcon.

Extensive spring and mid–summer trapping bolstered our knowledge of black ducks through band returns and recoveries.

To assist in our ecological study of the islands, GIS methods were used to produce accurate maps of the landscape.