Abundance of crossbills, Siskins and cone-crops

摘要

We present a more complete and definitive analysis than hitherto of the long runs of data on crossbill abundance and cone-crops in Finland and in Scotland. The abundance of Common Crossbills Loxia curvirostra in Finland was correlated with the abundance of cones of Norway Spruce Picea abies, the main food of this small-billed species, but not with the cone-crop of Scots Pine Pinus sylvestris. In Scotland, where the habitat was native Scots pinewood and the breeding crossbills are now known to be Scottish and Parrot, scotica and pytyopsittacus, their abundance was correlated with the cone-crop of Scots Pine, the main food of these larger-billed species.