The Red Crossbill (Loxia curvirostra) is the spruce forest specialist with a crossed bill tip, the male brick-red and the female olive-yellow, living almost entirely on spruce seeds. It breeds across vast stretches of the boreal forest belt spanning the northern hemisphere and, rather than being a true migrant, undertakes irruptive movements in some years, sometimes turning up far south of its normal range. Like all crossbills it has a proportionally large head and a distinctive bill in which the tip crosses, an adaptation for extracting seeds from cones, and considerable variation in colour, bill shape, and call has fuelled long-running debate over how many species or subspecies the group actually represents. It measures 15–17 cm, with a wingspan of about 27–30 cm and a weight of 35–50 grams; the male is orange to brick-red with brownish wings, the female olive-yellow to grey-green, and juveniles greyish and heavily streaked.
The most common call is a hard, metallic "glipp-glipp", often given by birds in flight or by flocks up in the spruce tops, while the song mixes twittering and harder notes. Red Crossbills occur in coniferous forest throughout Sweden, and the population fluctuates enormously from year to year depending on the spruce seed crop — this is a nomadic species that moves to wherever seed production is good, with some years bringing large-scale irruptions well outside the normal range. Breeding can begin unusually early, from January to April, even in sub-zero temperatures, as long as the cones are producing plenty of seed; the well-insulated nest is built high in a spruce, and the female lays 3–4 eggs, with the timing governed entirely by the seed year rather than the calendar. The diet is almost exclusively conifer seeds — chiefly spruce in Sweden, but also pine — extracted by using the crossed bill to force apart the cone scales so the tongue can pull the seed free.
Read about this species in Swedish →