Occurrence in different areas in different winters

As far as I am aware, few ring recoveries from different winters are yet available for any species of irruptive owls, which have been trapped only in relatively small numbers. However, the satellite-tagged Snowy Owls Nyctea scandiaca mentioned above were present in widely separated localities in different winters, and often moved long distances within a winter (Fuller et al. 2003). Another Snowy Owl was ringed near Edmonton in January 1955 and recovered 330 km to the southeast in Saskatchewan in January 1957 (Oeming 1957). There is also an intriguing record of a Long-eared Owl Asio otus ringed in California in April and recovered in Ontario in October of the same year (Marks et al. 1994). Presumably it returned to the breeding range in the interim.

Whatever the species, irruptive migrants do not necessarily remain in the same localities throughout a winter. Trapping has revealed considerable turnover in the individuals present at particular sites or the occurrence of the same individuals at widely separated sites in the same winter (for Great Grey Owl Strix nebulosa, see Nero et al. 1984; for Snowy Owl Nyctea scandiaca, see Kerlinger 1985, Smith 1997). The implication is that, in the non-breeding period, individuals move around, perhaps in continual search for good hunting areas. Local abundances of microtines can attract high densities of irruptive owls, and in these conditions some species form communal winter roosts, as recorded often in Long-eared Asio otus and Short-eared Owls A. flammeus (Cramp 1985) and also in Great Grey Owls (Nero et al. 1984). Recurrence at the same site in different winters has been recorded, but involved only a small proportion of the total caught (for Snowy Owl, see Smith 1997). In some years, the migrants may travel long distances without encountering any areas with abundant food, and in such cases their mortality rates are likely to be much higher than usual.

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