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Definite wintering grounds for any race uncertain. May be resident in Greater Antilles, though breeding visitor only to Puerto Rico from late Mar to mid-Aug. Present in Lesser Antilles from Mar/Apr to Aug/Sept. records in Jun from Guyana and in Jul from Trinidad apparently contradict theory that nominate race winters in Guyana. Absent in winter from Costa Rica, no certain records Nov-Mar, and majority, at least, leave Mexico N of Isthmus from Oct to Feb. Race borealis now known to winter somewhere in South America, as recorded late Sept to early Oct in Cauca, S Colombia. Migration from Central America to South America may be in part over Pacific, records offshore including 135 km off Guatemala's Pacific coast. Main spring arrivals: S California mid- May, British Columbia mid-late May to Jun. Main return migration: British Columbia late Aug to mid-Sept, S California late Aug to Oct. Rarely recorded from SE Farallon Is (42 km W of San Fransisco) mid-Jun and early Aug to early Oct. Race borealis occurs on Mexican Pacific slope Apr-May and Aug-Sept and offshore from Baja California S. Migration may occur Costa Rica Apr to early May and Sept to early Oct. Often migrates in large flocks, with groups of 300-400 noted during spring migration in California. Summer escape movements associated with passage of cyclones in British Columbia. Vagrant to E USA N to Massachusetts.   (del Hoyo J, Elliott A, Sargatal J (eds), 1999)

• digitised by GROMS, after del Hoyo J A Elliott; J Sargatal (eds) (1999) - www.hbw.com,
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  (A digitised version of this map is published in GIS shape format on the GROMS CD).