Red crossbills 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.