NATURAL HISTORY
WILSON’S PHALAROPE } Phalaropus tricolor
FAMILY: Scolopacidae
DESCRIPTION: Wilson's phalaropes are shorebirds about 9.2 inches long, with lobed toes and straight, thin bills. During the breeding season, the plumage of the female is a mix of pale bluish-grey and rust-like colors on the upperparts and white on the underparts. A conspicuous black band covers the sides of the face and neck. The male’s breeding plumage resembles that of the female but is duller. The nonbreeding plumage is similar in both sexes, with mostly pale grayish upperparts and white underparts.
HABITAT, RANGE AND MIGRATION: Wilson's phalaropes breed in wetland areas of the north-central United States and south-central Canada and spend winters on saline lakes in South America. During that impressively long southward journey (starting in late summer), these phalaropes make stops at “staging sites” to molt their feathers, stuff their bellies and rest. On their way south, most of these birds congregate at Great Salt Lake in Utah, with other important staging sites including Lake Abert in Oregon and Mono Lake in California. These big salt lakes attract hundreds of thousands of Wilson’s phalaropes, offering virtually inexhaustible abundance of invertebrates, which the southward-bound birds gorge on to help them rapidly molt their feathers and increase their fat reserves. On their return migration from South America in the spring, Wilson’s phalaropes are less picky about where they stop to rest, using a variety of habitats such as coastal lagoons.
BREEDING: In phalaropes, the typical bird sex roles are reversed: The larger, brighter-colored females pursue males, have multiple mates, compete for nesting territory, and aggressively defend their nests and mates. The male takes on the task of caring for chicks.
LIFE CYCLE: Wilson’s phalaropes may live up to 10 years.
FEEDING: Wilson’s phalaropes eat mostly aquatic insects and crustaceans like brine flies, alkali flies, and brine shrimp.
THREATS: In the United States, two of their biggest human-caused threats — both of which drain these lakes of water — are diversion of surface water and climate change. In 2022 Great Salt Lake’s water dropped to its lowest-ever recorded level, which increased the lake’s salinity to levels known to impair the survival of Wilson’s phalaropes’ favorite food sources (brine flies, alkali flies and brine shrimp). Meanwhile a large proportion of the lake’s formerly submerged microbialite rocks, which are critical to brine fly reproduction, were exposed to air and desiccated. Lake Abert’s water has almost completely disappeared twice in the recent past, causing major declines in phalarope numbers. At Lake Abert, the water almost completely disappeared in 2014–2015 and 2021–2022, resulting in major declines in phalarope numbers. Both the Great Salt Lake and Lake Albert are on a trajectory toward ecosystem collapse. Even at Mono Lake, phalaropes’ best-protected saline lake staging site, the water has stayed below the target level for more than 20 years — and its water is still being diverted.
POPULATION TREND: Although Wilson’s phalaropes have a relatively large population — about 1 million individuals — they’ve seen dramatic declines that put them all in danger. Thanks to loss of breeding habitat, the species underwent a significant decline in the early 20th century, and since 1980, it has declined by as much as 75% in North America1. Recent surveys at its three main staging sites — the pillars of the species’ transhemispheric range — show major declines compared to 1980s average high counts. At Great Salt Lake, by far the most important staging site, peak counts were one of the lowest on record for the site in 2022.
References
1. Conservation Plan for Wilson's Phalarope. Marcela Castellino, Ryan Carle, Arne J. Lesterhuis and Rob P. Clay. January 2024.
