Species fact sheet by Global Register of Migratory Species - www.groms.de

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Migratory or nomadic, when prey abundance declines; in California, one population stayed in a reserve, despite sharp drop in prey (vole) abundance, even continuing to catch same proportion of voles, but presumably requiring more time per capture. Transition between migratory and resident populations unknown, especially in S South America; birds from extreme S of range move N to C Chile in May-Jun; in Surinam, most birds are austral migrants, although a few breed. Congregates in large flocks in winter. Often roosts in flocks, usually in trees; one flock of over 100 birds roosted overnight in tall sugarcane, after staging on ground in nearby ploughed field.   (del Hoyo J, Elliott A, Sargatal J (eds), 1994)

• digitised by GROMS, after del Hoyo J A Elliott; J Sargatal (eds) (1994) - www.hbw.com,
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