Editor's Note: Based on genetic and morphological data, the Little Gull is now placed in its own genus, Hydrocoloeus. Future revisions of this account will adjust for this change.
The smallest gull worldwide, the Little Gull breeds in small numbers in North America but its main range is in the Palearctic. It now occurs regularly in small numbers along the eastern seaboard of the U.S. and on the Great Lakes, and it appears to breed mostly in the Great Lakes basin and in Canadian wetlands further north, usually near Common Terns (Sterna hirundo), Black Terns (Chlidonias niger), Forster's Terns (S. forsteri), or Ross's Gulls (Rhodostethia rosea). Although numbers are generally increasing in North America, few breeding locations are known.
The origin of Little Gulls in North America is something of a mystery. Some think that the species has always occurred here, albeit in small numbers. Others believe that it colonized via the Bering Sea, while many support the idea of one or more transatlantic colonizations from western Europe (reinforced by the recent return of a Swedish-banded chick in its first summer in Pennsylvania). The first documented nesting of this species in North America was not until 1962, on Lake Ontario, although the first recorded continental record was in 1819–1820, on the Franklin expedition ( Houston 1998a ). As of 1999 only 67 confirmed and probable nestings have been documented in North America, and these have occurred mainly in wetlands in the Great Lakes–St. Lawrence River basin, and the lowlands of Hudson and James Bays.
In North America the species is most frequently observed during winter and on migration in groups of 1–3, usually associated with larger flocks of Bonaparte's Gulls (Chroicocephalus philadelphia) along coasts or at larger inland lakes and rivers, although loose flocks of ≥100 have been recorded along the U.S. east coast and on the Great Lakes. Migration routes within North America are poorly known. The diet appears to consist mostly of small fish, invertebrates and some flying insects, but remarkably little ecological information exists for this species outside of Europe.
There have been no major biological studies of this species in North America. This account of its life history has collated all readily available published observational notes, regional bird atlases and unpublished records, and draws heavily on detailed studies in northwestern Europe of breeding and behavior (Veen Veen 1980 , Veen 1985 , Veen 1987 , Veen and Piersma 1986 ), distribution and migration ( Hutchinson and Neath 1978 , Smith 1987d , Messenger 1993 ), and the detailed species account presented by Cramp and Simmons ( Cramp and Simmons 1983 ). The main published North American papers are mostly from Canada, dealing with breeding records, distribution, and comments on possible origins ( Baillie 1963 , McRae Mcrae 1984 , Mcrae 1989 , Weseloh 1994 ).