Shorebirds: Winging Between Hemispheres

Q What is a shorebird?

A Shorebirds are a diverse avian group that include sandpipers, plovers, stilts, avocets, snipes, oystercatchers, turnstones, and phalaropes. These groups form the 49 species of shorebirds that are common in North America. They generally have small bodies, long, thin legs and no webbing on their feet. One of the interesting facts about shorebirds is their amazing variety of bill shapes and sizes. Differences in bill length and shape allow the many species of shorebirds to forage for food on dry soil or in shallow water. Shorebirds range in size from a few ounces to a pound or more and come in a variety of colors. Shorebirds migrate over incredible distances. The migratory paths used by shorebirds are influenced by geography and wind. Shorebirds are thought to have an internal compass for directional orientation which may be influenced by the sun, moon, position of stars, polarized light, magnetism, wind, photoperiod, or even olfactory cues (Kerlinger, 1995). Shorebirds are closely associated with wetland areas but do not swim. They are found in intertidal mudflats, salt marshes, and estuaries. Though many species can be found on ocean shores, a great many also use interior fresh water wetland areas of North America along their migratory routes and in breeding areas.

Q How many shorebirds are there?

Photo by Nancy McGihon

A Because shorebirds cover so much of the globe during their lifetime it is difficult to obtain accurate population numbers. Estimates put the numbers of some species, such as the Semipalmated Sandpiper, in the millions, while it is believed that the numbers of other species, such as the endangered Piping Plover, may only be a few thousand. .The best efforts to census shorebirds are made at known staging areas during migration. Censuses of several staging areas in recent years showed the following numbers for these species: At Delaware Bay; 600,000 shorebirds consisting mostly of Red Knots, Ruddy Turnstones, and Semipalmated Sandpipers; San Francisco Bay, California- 930,000 shorebirds of multiple species; Great Salt Lake, Utah- 600,000 Wilson’s Phalaropes and 300,000 Red-necked Phalaropes; Bay of Fundy, Canada- 1,000,000 shorebirds with Semipalmated Sandpipers numbering in the 100,000's. At sites in South America 500,000 Wilson’s Phalaropes and 20,000 Golden Plovers were counted in Mar Chiquita Cordoba, Argentina, 1,000,000 Semipalmated Sandpipers were recorded at Bigi Pan, Suriname, 2,000,000 Semipalmated Sandpipers and 50,000 Short-billed Dowitchers at Wia Wia, Suriname, and 750,000 Semipalmated Sandpipers, and 50,000 Lesser Yellowlegs at Coppename Rivermouth, Suriname. Though some of these numbers are high, studies indicate that the populations of many species of shorebirds are in decline.

Q Where do shorebirds live?

A Shorebirds cover vast amounts of territory during their life time. Most species breed in the arctic and sub arctic then migrate to wintering grounds in the Caribbean, Mexico, Central and South America, and in a few cases, to southern portions of the United States. During spring, summer and fall migration shorebirds visit specific stopover locations to rest and to replenish fat supplies which helps them to accomplish their long journeys. Many thousands of birds congregate in these staging areas where prey availability historically coincides with the migration period of the birds. One such area is Delaware Bay where the arrival of shorebirds parallels massive egg production by horseshoe crabs, a valuable food item for the birds. Other vital staging areas include the Copper River Delta in Alaska, Bay of Fundy, Canada, Cheyenne Bottoms, Kansas, The Great Salt Lake, Utah, and San Francisco Bay , California, as well as others in North America. Important Central and South American sites include Marisma Nacionales, Mexico, Paracas, Peru, Mar Chiquita Cordoba, Argentina, Lagoa de Peixe Rio Grande do Sul, Brazil, and the Suriname reserves of Wia Wia, Bigi Pan, and Coppename, among others.

Q What kinds of habitats do they need?

A Shorebirds use a variety of predominantly wetland habitats both on the coast and in interior regions. The type of habitat used depends on the activities of the birds such as feeding and breeding. In coastal regions shorebirds forage on intertidal mudflats, estuaries, and beaches (Meyers and Meyers, 1979). In interior areas of North America they frequent fresh water wetlands, mudflats, and saturated agricultural areas that are sparsely vegetated (Skagen and Knopf, 1994). The majority of shorebirds nest on the open tundra areas of the arctic and subarctic. Birds that breed in coastal areas do so on sandy beaches, gravelly areas, or as in the case of Willets, in vegetated marsh areas. Birds nesting in interior regions will generally breed in or near wetlands in sites with sand or gravel substrates (surfaces). Some will also choose vegetated areas in which to nest.

Q When do shorebirds migrate?

A Shorebird migration occurs during the spring, summer, and fall months. The majority of shorebirds migrate to the arctic circle in the spring and must get there quickly to take advantage of abundant food resources and to make the most of the short arctic summer (Burger,1984). A few species such as the Piping Plover do not journey as far north and instead reproduce in the coastal and interior regions of the United States. Once breeding is complete shorebirds begin their return journey southward. Some shorebirds leave the arctic as early as July. The return to wintering grounds is more leisurely and continues throughout the fall months. Most shorebirds spend the winter in the warmth of the tropics and subtropics.

Q How far do they migrate?

A Many shorebirds are capable of flying great distances making migratory journeys from the furthest tip of South America to the high arctic of Canada and the U.S. Though they stop at specific staging areas to refuel along their migratory routes, birds such as the Bristle- thighed Curlew are capable of flying 1,200 to 3,000 mile segments of their journey nonstop. During their trip southward in the fall, Semipalmated Sandpipers often fly from the North Atlantic coast to the refuges of Suriname in South America without stopping; a journey of about 2,000 miles (O’Reilly and Wingfield, 1995). Migratory routes and stopover points occur on both coasts and the interior of North America taking birds from the arctic to as far south as Tierra del Fuego, South America.

The Red Knot can fly extraordinary distances, migrating from the Arctic Circle to as far as Tierra del Fuego, South America.

Q Where do shorebirds breed?

A The majority of shorebird species breed on the tundra of the arctic and sub arctic regions. Some do breed in or near wetland areas in the temperate zones of coastal and interior North America. Of these, shorebirds such as Willets can nest in vegetated marsh areas, American Oystercatchers and Piping Plovers on sandy beaches, and Common Snipes in upland/ wet meadow areas. Killdeer nest on gravel type substrates in open areas with little vegetation, and nesting locations can range from pastures to roadsides. The Woodcock, a more upland bird, breeds in young forests with very low vegetation and many clearings. Moist slopes and fields are usually nearby (Johnsgard, 1981).

Q What are their breeding habits like?

A Many shorebird species are monogamous with one male and one female bird paired to nest and raise offspring. Incubation of the young is often shared by both sexes but in some cases such as the Spotted Sandpiper, mates are chosen by the female and nesting and raising of the young is performed by the male. This system is known as polyandry. For many species, males arrive first at northern breeding areas to stake out a territory. When mate selection is complete nesting begins. Most species of shorebirds lay no more than 4 eggs. Small birds such as Western and Least Sandpipers incubate their eggs from 19 to 22 days. Medium- sized birds such as the Red Knot incubate their eggs from 23 to 25 days, and large shorebirds such as Curlews from 26 to 32 days. Shorebird young are precocial, having the ability to feed themselves very soon after hatching (Erckmann, 1983). Shorebird chick mortality is often high due to starvation, exposure to the elements, and predation by gulls, foxes and other mammals. Most chicks are sufficiently grown and able to fly after about a month at which point the parents leave them. Adults fly south before juveniles. Females usually leave first followed by males. Juveniles continue to feed, following the adults south as much as a month later (Morris, 1996).

Q What do shorebirds eat?

A Shorebirds eat a variety of invertebrate prey. Different species of shorebirds forage in different ways. Plovers have large eyes and locate their food visually by picking it from the surface of saturated soil areas. Sandpipers have eyesight that is less acute and generally find food by touch, probing soft substrates with their bills. Shorebird diets consist of polychaete and oligochaete worms, insect larva, and aquatic insects such as water boatmen. Other food items include amphipods, copepods, crustaceans, and mollusks. Shorebirds of different species can and do forage together. Because bill length and shape varies from species to species, birds can pursue different prey in the same area at the same time without competing with each other. Because of varying bill lengths, each bird species food source is at a different depth in the substrate. Mixed species flocks of shorebirds are a common sight. In coastal areas shorebird feeding schedules are influenced by the cycle of the tides. Changes in tidal cycles expose foraging areas on beaches and in intertidal mudflats and estuaries for a period during the day. At other points during the cycle the water in these same areas becomes too deep for shorebirds to feed effectively. Some shorebirds do forage at night though how long they forage and how successful they are is difficult to determine (Robert and McNeil, 1989).

Q Are shorebirds threatened?

A Some shorebirds such as the Piping Plover, Snowy Plover, and the Eskimo Curlew, are endangered. It is estimated that fewer than 100 Eskimo Curlews remain in Canada, and it is believed that there are only approximately 5,500 breeding adult Piping Plovers left. In addition, the Mountain Plover is in decline in the western U.S. due to degradation of its wintering grounds. While some shorebird populations remain stable, census data in eastern Canada indicates that Least Sandpipers, Semipalmated Sandpipers, Short-billed Dowitchers, Red Knots, and Black- bellied Plovers all show population declines (Morrison, 1994).

Piping Plover

Q What are the reasons for their decline?

A Over hunting of the Eskimo Curlew many years ago is the main reason for its drastic decline and, replacement of crucial native grass habitat with agriculture in central North America sealed its fate. Populations never recovered. Today the greatest reason for the decline of shorebird populations is loss of wetland habitat. More than 50 percent of Willets have been lost nationwide for this reason. Development of coastal and other wetland areas for human use has significantly reduced areas where shorebirds forage and reproduce. In the case of the Piping Plover, which often nests on coastal beaches, reproduction is frequently disrupted by human disturbances (beachgoers, off road vehicles). Many nesting birds that are continually disturbed do not rebuild their nests elsewhere resulting in the production of fewer offspring. Habitat loss in shorebird staging areas has also had an impact. Many areas that have historically supported birds on their flights north and south have reduced in size or the environment and food supply of these areas has been degraded(Pfister, et al, 1992). For example, because horseshoe crab eggs are such an important source of food for shorebirds migrating through the staging area of Delaware Bay, commercial over harvesting of these animals may also be a reason for lower shorebird numbers. These seasonally concentrated areas of shorebird activity can be vulnerable to ecological disasters such as oil spills or the spread of disease as well. Were such an event to occur at a major shorebird staging area it would be possible to wipe out a significant portion of the overall bird population. Changes in sea level due to global warming is also of potential concern. Even a small increase in global temperature could be enough to raise water levels to the point that many coastal wetland areas would be destroyed. Habitat loss in wintering grounds in Central and South America also affects shorebird numbers. Loss of habitat decreases food availability causing birds to have to work harder to survive. Other reasons for lower shorebird numbers include pollution, pesticide use, and the often unpredictable harsh weather conditions during the breeding season in the arctic (Howe, 1989).

Q What is being done to help shorebirds survive?

A Many organizations are now working together to aid shorebird survival and to preserve shorebird habitat. The Manomet Center for Conservation Sciences, a research organization dedicated to preserving our natural resources, organized the International Shorebird Survey (ISS) many years ago to census shorebird populations at migratory stopover points during the spring and fall. Information gathered on the location of these staging areas, bird numbers, and migratory routes has increased knowledge of shorebird population trends. A major contribution to shorebird conservation came with the organization of the Western Hemisphere Shorebird Reserve Network (WHSRN) in 1985. WHSRN consists of wildlife agencies, scientists, private conservation groups, and governments that endeavor to preserve and manage wetland habitat on a hemispheric scale to aid shorebird survival. WHSRN emphasizes the importance of specific staging areas used by large numbers of shorebirds on their migratory flights. A U.S. shorebird conservation plan is presently in development. Scientists, educators, and habitat managers, are developing a plan that will provide short and long term research, population monitoring, and habitat management strategies for shorebirds. Education and public outreach programs are also being designed to increase public awareness for the need to preserve these graceful birds and the habitats that are as important to our health and well being as it is to theirs.

Q What can I do to help conserve shorebirds?

A One good way to help conserve shorebirds is to support the Federal Duck Stamp Program. Revenues from these stamps provide funds for the purchase of wetlands that are added to the National Wildlife Refuge System. It is also important to be well informed about shorebird issues. Visit your nearest National Wildlife Refuge or other protected area to view shorebirds and to learn more about their habits. You can also visit the Shorebird Sister Schools Program web site, an educational program designed to teach about the migration of shorebirds from their southern wintering grounds to their nesting sites in the arctic.

Literature Cited

Botton, M.L, Loveland, R.E., and Jacobsen, T.R. 1994. Site Selection of Migratory Shorebirds in Delaware Bay and its Relationship to Beach Characteristics and Abundance of Horse shoe Crab (Limulus polyphemus) eggs. Auk. 111 (3).

Burger, J. 1984. Abiotic factors Affecting Migrant Shorebirds. In: Shorebirds, Migration and Foraging Behavior (J. Burger and B. Olla, eds.). Plenum Press, New York.

Howe, M.A., P.H Geissler, and B.A. Harrington. 1989. Population Trends of North American Shorebirds Based on the International Shorebird Survey. Biological Conservation. 49

Erckmann, W.J. 1983. The Evolution of Polyandry in Shorebirds: An Evaluation of Hypotheses. In: Social Behavior of Female Vertebrates. (Wasser, S.K, ed.). New York Academic Press, N.Y

pp. 113-168.

Helmers,D.L. 1992. Shorebird Management Manual. Western Hemisphere Shorebird Reserve Network, Manomet, Ma. 58 pp.

: 185-199.

Johnsgard, P., 1981. The Plovers, Sandpipers, and Snipes of the World. University of Nebraska Press, Lincoln, NE.

Kerlinger, P., 1995. How Birds Migrate. Stackpole Books, Mechanicsburg, PA.

Meyers, J.P. and L.P. Meyers, 1979. Shorebirds of Coastal Buenos Aires Province, Argentina. Ibis. 121: 186-200.

Morris, A., 1996. Shorebirds: Beautiful Beachcombers. North Woods Press, Inc. Minocqua, WI.

Morrison, R.I., 1994. Shorebird Population Status and Trends in Canada. In: Bird Trends. A Report on Results of National and Regional Ornithological Surveys in Canada. Environment Canada. 3: 1-20.

O’Reilly, K. and Wingfield, J.C., 1995. Spring and Autumn Migration in Arctic Shorebirds: Same Distance, Different Strategies. American Zoologist. 35 (3)

Page, G.W and R.E. Gill, 1994. Shorebirds in Western North America: Late 1800's to Late 1900's. Studies in Avian Biology. 15: 147-160.

Pfister, C.,B.A. Harrington, and M. Lavine, 1992. The Impact of Human Disturbance on Shorebirds at a Migration Staging Area. Biological Conservation. 60: 115-126.

Robert, M and R. McNeil, 1989. Comparative Day and Night Feeding Strategies of Shorebird Species in a Tropical Environment. Ibis. 131: 69-79.

Skagen, S.K. and Knopf, 1994. Migrating Shorebirds and Habitat Dynamics at a Prairie Wetland Complex. Wilson Bulletin. 106 (1): 91-105.

Shorebird Migrations: Fundamentals for Land Managers in the United States.1999. Ducks Unlimited with the USDA Forest Service.

Transcripts from the Western Hemisphere Shorebird Reserve Network Workshop. May 11-13, 1995. Ottawa, Canada.

Written by Dawn O'Harra and posted to this website on 8/99. Last revised on 9/29/2005.

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