The Red-necked Phalarope, a member of the shorebird family, is functionally among the world's smallest seabirds. Smallest and daintiest of the 3 phalarope species, it spends up to 9 months of the year at sea, riding on a raft of dense belly plumage and feeding on tiny planktonic invertebrates at oceanographic fronts, convergences, and other discontinuities. During that time, both sexes are largely white with gray mantles and striking piratical black eye-patches, and are difficult to distinguish from their equally pelagic congener, the Red Phalarope (Phalaropus fulicaria), except by the fineness of their bills and bodies. Red-necked Phalaropes are famous, as are the other 2 species of phalarope, for lifting aquatic prey within reach by rapidly spinning in tight circles in a manner reminiscent of a slightly demented toy.
Formerly known as the Northern Phalarope, this species breeds widely across the Holarctic. Like other phalaropes, it is a polyandrous species in which sex roles are reversed; breeding females are distinguishable by brighter plumage than males and by slightly larger body size. The species is largely nonterritorial, but females fight ferociously over males, which provide all parental care. Nests are terrestrial, but the affinity of this species for water is evident through the feeding, fighting, and copulation on almost every small tundra pond.
Postbreeding, Red-necked Phalaropes migrate to pelagic wintering areas either over the open ocean or via inland bodies of water of all sizes and description. In western North America, tens of thousands use hypersaline lakes as fueling stations on their way south to the Humboldt Current off Peru and Ecuador. In eastern North America, massive flocks totaling millions formerly staged in fall in the western Bay of Fundy; in recent years, these have disappeared. This troubling development remains a puzzle, like much of the pelagic biology of this species, and has been mirrored by similar declines in numbers of migratory phalaropes observed off Japan.
The circumpolar distribution and sex-role reversal of this species has generated interest in its breeding biology since the early part of the twentieth century. Much of what is known about breeding behavior of Red-necked Phalaropes was first described in some form in Tinbergen's ( Tinbergen 1935 ) detailed observations in Greenland, and Hildén and Vuolanto's ( Hildén and Vuolanto 1972 ) multiyear study in Finland. More recently, the work of Colwell, Reynolds, and their colleagues in Canada (e.g., Colwell et al. Colwell et al. 1988a , Colwell et al. 1988b , Colwell et al. 1988c ; Reynolds and Cooke 1988 ; Reynolds 1987a ; Reynolds et al. 1986 ), and Schamel and Tracy ( Schamel and Tracy 1988 , Schamel and Tracy 1991 ) in Alaska has broadened our knowledge of the breeding biology of this species. The endocrinology of sex-role reversal in phalaropes was revealed by Höhn ( Höhn 1963 , Höhn 1970 ), Gratto-Trevor et al. ( Gratto-Trevor et al. 1990a , Gratto-Trevor et al. 1990b ), and Oring and Fivizzani ( Oring and Fivizzani 1991 ).
In contrast, very little is known about the migratory or wintering biology of the species at sea; our most detailed information about migration comes from a single saline lake in California ( Winkler et al. 1977 , Jehl 1986b , Rubega and Inouye 1994 ) and the Bay of Fundy ( Mercier 1985 , Mercier and Gaskin 1985 , Brown and Gaskin 1988 ). Even less is known about its biology at sea, because of the logistical difficulties of finding and observing the species offshore. Since Murphy's ( Murphy 1936 ) account of vast flocks wintering in the Humboldt Current, a few workers have added distributional and diet data, and confirmed the affinity of these birds for oceanographic features that concentrate prey near the surface ( Briggs et al. 1984 ; Haney Haney 1985c , Haney 1986b ; Tyler et al. 1993 ; Wahl et al. 1993 ).