The crossbill is a genus, Loxia, of birds in the finch family (Fringillidae), with six species. These birds are characterised by the mandibles with crossed tips, which gives the group its English name. Adult males tend to be red or orange in colour, and females green or yellow, but there is much variation. Crossbills are specialist feeders on conifer cones, and the unusual bill shape is an adaptation which enables them to extract seeds from cones. These birds are typically found in higher northern hemisphere latitudes, where their food sources grow. They irrupt out of the breeding range when the cone crop fails. Crossbills breed very early in the year, often in winter months, to take advantage of maximum cone supplies. Systematics and evolution The genus Loxia was introduced by the Swedish naturalist Carl Linnaeus in 1758 in the 10th edition of his Systema Naturae. The name is from the Ancient Greek , "crosswise". The Swiss naturalist Conrad Gessner had used the word Loxia for a crossbill in 1555 in his Historiae Animalium. The type species was designated as Loxia curvirostra (red crossbill) by George Robert Gray in 1840. Analysis of mitochondrial cytochrome b sequence data indicates that the crossbills and redpolls share a common ancestor and only diverged during the Tortonian (, Late Miocene). The research suggests that the genera Loxia and Carduelis might be merged into a single genus, for which the name Loxia would then have priority. But this would imply changing the name of a large number of species, and given that the adaptations of the crossbills represent a unique evolutionary path (see Evolutionary grade), it seems more appropriate to split up the genus Carduelis as it had already been done during most of the 20th century. Unfortunately, the fossil record is restricted to a Late Pliocene () species, Loxia patevi, found at Varshets, Bulgaria. The species of crossbills are difficult to separate, and care is needed even with the two-barred and Hispaniolan crossbills, the easiest. The other species are identified by subtle differences in head shape and bill size, and the identification problems formerly led to much taxonomic speculation, with some scientists considering that the parrot and Scottish crossbills and possibly the Hispaniolan and two-barred crossbills are conspecific. The identification problem is least severe in North America, where only the red and white-winged species occur, and (possibly) worst in the Scottish Highlands, where three species