Red Crossbills (Loxia curvirostra) are finches with highly specialized, crossed bills and long, pointed wings. Male Red Crossbills are brick-red with black wings and no white wing-bars. Females are greenish-yellow with black wings and no wing-bars. Juveniles are streaked brown. The bill size of Red Crossbills varies considerably and correlates with distinct habitat and food preferences as well as flight calls. These characteristics can be used to split Red Crossbills into eight distinct types, and it is likely that the species will be divided into multiple species in the future.
Red Crossbills typically inhabit mature conifer forests, and different types tend to specialize on preferred trees, including western hemlock, Ponderosa pine, lodgepole pine, Sitka, and Engleman spruce.
- Because this species can breed throughout most of the year, its molts and plumages vary more than those of other North American passerines. Juveniles hatched during summer molt only between late summer and late autumn (at the same time adults molt). Many (but not all) juveniles hatched earlier (from late winter and early spring) begin to molt 100-110 days after hatching and then again during the main molt period in the summer.
- A crossbill’s odd bill shape helps it get into tightly closed cones. A bird’s biting muscles are stronger than the muscles used to open the bill, so the Red Crossbill places the tips of its slightly open bill under a cone scale and bites down. The crossed tips of the bill push the scale up, exposing the seed inside.
- The Red Crossbill shows a great deal of variation in bill shape and voice, and it may in fact be composed of several different species. Eight different flight call types have been described north of Mexico, and birds giving each type have slightly differently shaped bills and prefer to feed on different tree species with differently sized cones.