Phalaropus tricolor (Vieillot, 1819)
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Basis for Listing
The Wilson's phalarope is a wetland species that breeds primarily in the northwestern quarter of the United States and southwestern Canada. A recent range expansion is suggested by the increasing number of breeding records from southeastern Alaska, New Mexico, Massachusetts, and other areas outside the species' previously-documented breeding range. Wilson's phalaropes formerly occurred throughout most of the prairie region of Minnesota. Roberts (1932) commented that the species was abundant prior to 1900, with every large slough or shallow lake harboring many pairs in the nesting season. By the turn of the century, however, the species experienced a sudden and somewhat puzzling decline. It began to recover during the 1920s, but due to the continued loss of its prairie wetland habitat, it has never attained its former level of abundance (Colwell and Jehl 1994).
Wilson's phalaropes are a relatively small, long-legged shorebird. They are unique among Minnesota birds in that they are one of only a few species in which the female is much more brightly colored than the male. Wilson's phalaropes can be distinguished from most other shorebirds by the bright coloration on their neck and head. Additionally, unlike other shorebirds, Wilson's phalaropes often feed while floating on the water, sometimes spinning like tops to stir up aquatic invertebrates. The relatively long, thin bill, and bold blackish stripe on the neck and face distinguish the Wilson's phalarope from the red-necked phalarope (Phalaropus lobatus), which is a migrant in Minnesota.
In Minnesota, Wilson's phalaropes are most frequently found in wet prairie, rich fen, and other grass- or sedge-dominated wetlands. The presence of short vegetation in or adjacent to shallow pools of open water is an important microhabitat feature. Human-altered habitats, particularly flooded pastures and municipal wastewater stabilization ponds, may also provide suitable habitat. Most Wilson's phalarope nests are located in the wet meadow zone of wetlands or in nearby upland prairie.
Biology / Life History
Wilson's phalaropes overwinter in salt marshes and wetlands in Bolivia and Argentina. They are highly gregarious and social throughout the year, gathering in large flocks during migration and while overwintering. They also nest less than 5 m (16.4 ft.) apart during the breeding season. While generally non-territorial, Wilson's phalaropes may defend feeding sites when food is scarce. Wilson's phalaropes are well known for their reversed sex-role mating system, in which females compete for mates upon arrival at the breeding grounds in early May. Nests are built by males and are little more than shallow scrapes in areas of dense vegetation. Occasionally, the nests will have plant matter bent over the top to provide additional cover. Females lay a clutch of 4 eggs, and while the male incubates, the female may compete for additional mates. The chicks are precocial and are able to swim an hour after hatching. While able to find their own food, chicks are defended by the male until they are able to fly, though the exact duration of parental care is unknown. Food habits vary seasonally and between the sexes. Females tend to be more aquatic than males and eat mainly crustaceans and other aquatic invertebrates. During the breeding season, males and chicks feed on invertebrates found in terrestrial habitats along shorelines, but become more aquatic later in the season (Colwell and Jehl 1994).
Conservation / Management
Because microhabitat conditions are very important to Wilson's phalaropes, water conditions greatly influence habitat use. The shallow wetlands on which this species depends are very sensitive to alteration, especially drainage and degradation resulting from agricultural activities. Artificial manipulation of water levels in sedge wetlands may promote vegetation, such as cattails, unsuitable to Wilson's phalaropes. When water levels are low, wetlands may be avoided due to the lack of standing water. Wetlands dominated by shrubs are also avoided. Burning appears to be an important factor in reducing shrub densities in sedge wetlands. Therefore, prescribed burning of wetlands can be an effective management practice for maintenance of Wilson's phalarope habitat. Human-altered habitats, such as wastewater stabilization ponds and flooded, fallow fields, may be utilized by Wilson's phalaropes because they provide necessary microhabitat conditions lacking in native habitats. Areas where observations of Wilson's phalaropes repeatedly occur should be monitored for nesting activity. Habitat where Wilson's phalaropes are known to nest should be protected, and potentially suitable habitat should be maintained to encourage future nesting.
Conservation Efforts in Minnesota
The Wilson's phalarope is considered a priority species under the Minnesota DNR Nongame Wildlife Program's Ten-Year Strategic Plan. The Nongame Wildlife Program has provided training and technical assistance to government agencies and private conservation organization that are incorporating the needs of shorebirds into habitat conservation and restoration. This shorebird is also a target species for the Minnesota Biological Survey (MBS). Between 1988 and 2008, MBS conducted intensive searches for breeding Wilson's phalaropes in many counties within the potential nesting range of the species. As a result, 60 new breeding season records were collected in 22 counties. However, in many areas it appears that suitable Wilson's phalarope habitat exists but is not occupied. Also, nowhere have Wilson's phalaropes been found nesting in significant numbers. Protection of wetlands and adjacent upland habitat will ensure the presence of potential breeding habitat for Wilson's phalaropes in Minnesota.
References and Additional Information
Colwell, M. A., and J. R. Jehl, Jr. 1994. Wilson's Phalarope (Phalaropus tricolor). Number 83 in A. Poole and F. Gill, editors. The birds of North America. The Birds of North America, Inc., Philadelphia, Pennsylvania.