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Wilson’s Phalarope is the largest and most terrestrial of the three phalarope species, which are well known for their reversed sex-role mating system. Larger and more brightly-plumaged females compete for mates and are sometimes polyandrous, whereas males provide all parental care. The species is nonterritorial, although birds occasionally defend feeding sites when food is scarce.
Unlike the other phalarope species, which have Holarctic breeding ranges and pelagic nonbreeding distributions, Wilson’s Phalarope breeds exclusively within the Nearctic, and its non-breeding distribution is entirely continental. It breeds at shallow wetlands of interior western North America but for most of the year is a salt-lake specialist.
After the breeding season, virtually all adults undertake a molt migration and stage, often in huge flocks, at hypersaline/alkaline lakes of western North America, before migrating to similar wintering habitats mainly in the altiplano of Bolivia and Argentina. Small numbers winter at wetlands in the pampas and as far south as Tierra del Fuego. Although knowledge of this species’ biology at breeding sites and migratory staging areas is good, relatively little is known of its habits in wintering areas.
While loss of prairie wetlands in the early to mid-twentieth century reduced habitat for this phalarope, and likely its numbers as well, its range has been expanded dramatically in recent decades, with breeders now reported from regions as far east as Massachusetts, as far south (and west) as New Mexico, and as far north as Alaska and the Yukon.