Other crossbills

In Eurasia, where the Two-barred Crossbill Loxia leucoptera feeds primarily on larch, it may not suffer such extreme fluctuations in food supply as the spruce-feeding Common Crossbill L. curvirostra. This is because larch cones remain on the tree with some of their seeds for 2-3 years, so poor crops can be enhanced by carry-over from previous years. This may explain why this species is much less irruptive in the western Palaearctic than the Common Crossbill, and appears in only very small numbers south of the boreal zone, mostly along with Common Crossbills. Irruptions into Scandinavia occur during cone failures in larch further east in Russia. They tend to occur from late summer, as new cones ripen, but at longer intervals than the 2-4 years recorded in North America (Bock & Lepthien 1976, Larson & Tombre 1989). Two-barred Crossbills L. leucoptera have come to Britain mainly in the same years as Red (Common) Crossbills, though much less frequently (Newton 1972), with larger numbers than usual recorded in 1889, 1956, 1979, 1985-1987 and 1990 (Cramp & Perrins 1994). Following the irruption of Two-barred Crossbills in 1990, successful nesting of this species was recorded near Berlin in 1991, some 1700 km southwest of the usual breeding range (Fischer et al. 1992), and after the invasion of 1956 nesting was recorded in Sweden, 600 km east of the usual breeding range (Markgren & Lundberg 1959).

Small numbers of Parrot Crossbills L. pytyopsittacus also appear in Britain, mainly in the same years as Common Crossbills. Relatively large invasions occurred in 1962, 1982 and 1990 (Catley & Hursthouse 1985, Rogers 1992). Unlike the other European crossbills, Parrot Crossbills move mainly in the autumn, in keeping with the different phenology of their food plant, as the seeds in new pine cones are not normally developed much before September. One individual that was ringed as a nestling in Norway was recovered in the breeding season three years later 340 km to the east, in Sweden (Norwegian Ringing Report, 1966-67). Like other crossbills, Parrot Crossbills may nest in peripheral invasion areas for a year or two, before disappearing, as recorded occasionally in Denmark, Britain and the Netherlands.

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