Detection and identification of a cryptic red crossbill call type in northeastern North America

Red crossbills ( Loxia curvirostra ) are the archetypal example of a taxon with high infraspecific diversity in traits including bill size and especially vocal characteristics. Currently, at least 11 different call types in North America have been recognized. We hypothesize that a variant call within type 10 has been overlooked and is a distinct type. Principal component analysis showed that the inverted “V” of these calls is consistently and demonstrably different from similar calls of birds previously categorized as Type 10 variants. We argue these calls should be treated separately as a distinct type, Type 12. Due to increasingly available recordings of crossbills gathered and archived into public databases by birders, our analyses reveal that this call type is predominantly distributed across northeastern North America. Although crossbill types do not always map to formerly described subspecies, we also argue that Type 12 likely matches the historically described L. c. neogaea , the “old Northeastern subspecies”.