Synthesis of U.S. Geological Survey Science for the Chesapeake Bay Ecosystem and Implications for Environmental Management

Chapter 14: Changes in Food and Habitats of Waterbirds
By Matthew C. Perry

The Chesapeake Bay is an important area for waterbirds because it is located in the Atlantic Flyway. The Bay winters over one million ducks, geese, and swans annually, provides stopover habitat to thousands of migrating marsh, shore, and wading birds, and maintains substantial breeding populations of colonial waterbird species. While migratory bird protection is not one of the goals in Chesapeake 2000, the DOI has the responsibility to restore populations under the North American Waterfowl Management Plan. The USGS supported the DOI management need through studies addressing the factors affecting waterbird populations and their habitats. The synthesis of USGS findings is focused on loss of food sources and alteration of habitat for waterbird populations.

During 2001–06, USGS focused on the factors affecting the declines in sea duck populations, which are a group of ducks not frequently seen by the public due to the fact that they feed in deep water in the Bay. USGS findings indicate that these declines could be from changes in diversity and abundance of shellfish and other benthic foods (Kidwell and Perry, 2005; Perry and others, 2005; Niven and others, 2005). The declines of food sources, such as mussels and other invertebrates, and changes in foodweb and habitat relations (fig. 14.1) have possibly contributed to the declines in sea ducks. The findings imply that the collapse of the once vast native oyster population has possibly had a major impact on sea ducks by removing mussels and other invertebrates associated with the oyster bars. Decline in these communities represents a major loss in foods and foraging habitat available to a variety of waterbirds. The findings imply that if oyster populations and other invertebrates are restored in the Bay, populations of waterbirds that depend on them as a food source could also increase.

Food sources and habitats of waterbirds also are affected by exotic and invasive species. The exotic mute swan has increased its population size in Chesapeake Bay (Maryland and Virginia) to approximately 4,500 since 1962, when five swans were released in the Bay (Perry, 2004). The Bay population of mute swans now represents 30 percent of the total Atlantic Flyway population (12,600), and had a phenomenal increase of 1,200 percent from 1986 to 1999. Unlike the tundra swans that migrate to the Bay for the winter, the mute swan is a year-round resident. There are concerns about their impact on nesting native waterbirds and the consumption of SAV. Although data on the consumption of SAV by nesting mute swans and their offspring during the spring and summer are limited, USGS studies of their food habits show that mute swans rely heavily on SAV during these months (Perry and others, 2004). It has been reported that a mute swan can consume about 8 pounds of SAV per day, raising concerns among resource managers (Perry and others, 2004).

While concern grows over the increasing number of exotic mute swans on the Chesapeake Bay, less attention seems to be given to the highly familiar and native Canada goose, which has developed unprecedented non-migratory, or resident, populations over time. Although nuisance flocks of Canada geese have been well developed at city parks, athletic fields, and golf courses over the past three decades, recent expansion of populations to an estimated one million birds in the Atlantic Flyway, and to over 500,000 in Maryland, carries a threat of broader ecological consequences. USGS findings revealed that herbivory by invasive resident Canada geese has led to a major decline of wild rice in tidal marshes of the Patuxent River and probably in other areas (Haramis and Kearns, 2004). Wild rice is a critical fall resource to a variety of migrating wetland birds, especially sora rails, and rails have declined in abundance with loss of these habitats. Chesapeake Bay historically provided valuable habitat for wintering rails and several species have supported hunting seasons. These findings imply that better understanding of factors affecting food sources and habitat of waterbirds will give managers more reliable information to manage and regulate waterbird populations. Monitoring the effectiveness of management plans of bird populations that are considered invasive or problematic (such as mute swans and resident geese) will be needed to determine if strategies need to be revised.

Figure 14.1. Generalized food web for some of the major waterbirds that frequent the Chesapeake Bay (modified from Perry and others, 2005). Food sources and habitats of waterbirds are affected by multiple factors, including exotic and invasive species. A better understanding of these factors will provide managers with stronger information to manage and regulate populations.

Collection of benthic samples which are used to help determine food sources for sea ducks in Chesapeake Bay. (Photograph courtesy of Matthew Perry, U.S. Geological Survey.)

References

Haramis, G.M., and Kearns, G.D., 2004, Invasive herbivory: Resident Canada geese and the decline of wild rice along the tidal Patuxent River, p. 37–38 in Perry, M.C., ed., Mute swans and their Chesapeake Bay habitats, in Proceedings of a symposium, U.S. Geological Survey Information and Technology Report 2004–0005, 59 p.

Kidwell, D.M., and Perry, M.C., 2005, Delineation of surf scoter habitat in Chesapeake Bay, Maryland: Macrobenthic and sediment composition of surf scoter feeding sites, [abs.] in Perry, M.C., Second North American Sea Duck Conference, November 7–11, 2005, Annapolis, Maryland, Program and Abstracts, USGS Patuxent Wildlife Research Center, Maryland, 123 p. (p. 91).

Niven, D.K., Sauer, J.R., and Butcher, G.S., 2005, Population trends of North American sea ducks based on Christmas bird count and Breeding Bird Survey data, [abs.] in Perry, M.C., 2005, Second North American Sea Duck Conference, November 7–11, 2005, Annapolis, Maryland, Program and Abstracts, USGS Patuxent Wildlife Research Center, Md., 123 p. (p. 101)

Perry, M.C., ed., 2004, Mute swans and their Chesapeake Bay habitats, proceedings of a symposium: U.S. Geological Survey Information and Technology Report 2004–0005, 59 p.

Perry, M.C., Osenton, P.C., and Lohnes, E.J.R., 2004, Food habits of mute swans in Chesapeake Bay, p. 31–36 in Perry, M.C., ed., Mute swans and their Chesapeake Bay habitats, proceedings of a symposium: U.S. Geological Survey Information and Technology Report 2004–0005, 59 p.

Perry, M.C., Osenton, P.C., Wells-Berlin, A.M., and Kidwell, D.M., 2005, Food selection among Atlantic Coast sea ducks in relation to historic food habits, [abs.] in Perry, M.C., Second North American Sea Duck Conference, November 7–11, 2005, Annapolis, Maryland, Program and Abstracts, USGS Patuxent Wildlife Research Center, Maryland, 123 p. (p. 105).

Birds on the water at Blackwater National Wildlife Refuge. Photograph by Heather Lane, IAN Image Library (www.ian.umces.edu/imagelibrary/).