Crossbill

Crossbill, any species, of the Passerine genus Loxia, in which the lower mandible curves upwards to the right or left of the upper mandible. Buffon described this formation as an "error of nature": it is an excellent adaptation of means to an end - to enable these birds to break up the fruits of conifers to obtain the seeds, on which they feed, and it is also used as a climbing organ. The Common Crossbill (Loxia curvirostris) is from six inches to seven inches long; the young males are greenish-brown, with an olive tinge, and speckled with dark brown; after the first month a red tinge is acquired, and after the second the plumage becomes olive brown, washed with greenish-yellow on the back. It is a somewhat irregular British visitant, frequently staying to breed. L. pityopsittacus (the Parrot Crossbill) and L. bifasciata (the Two-barred Crossbill) more rarely occur. All the Crossbills are gregarious, and frequent pine-forests in the northern hemisphere.