The crossed bill, seemingly freakish, is actually a unique, highly efficient adaptation to extract seeds from conifer cones. Some individuals have beaks crossing left over right, others right over left allowing some flock members to feed right side up, the others upside down. This permits all flock members to feed without competition. Found across conifer forests of the northern hemisphere south to Nicaragua, North Africa, the Middle East, and Korea, crossbills vary greatly in body and beak size in adjustment with natural selection to match beak and cone sizes in different geographical areas. Cone failures trigger massive migrations to other regions where – if food is adequate – nesting can take place spontaneously any time of year. Some populations have different vocalizations, leading to speculation separate species may be involved. DNA does not currently support this.

I and many other ornithologists find this species of nomadic occurrences a subject of intense interest. When affiliated with the University of Minnesota, I collected the largest number (at the Bell Museum of Natural History) of this species from a single location in North America and documented the presence of 6 different subspecies in Wadena County, Minnesota in different years – mostly from one tree!