Intraspecific variation in the hindlimb musculature of the Northern Flicker

Abstract

We carried our bilateral dissections of the hindlimb musculature of 51 preserved specimens of the Northern Flicker (Colaptes auratus) in order to assess the degree of anatomical variation in a non-passeriform taxon. We found three variations. M. iliofibularis, described as typically single-headed in the Piciformes, had two distinct heads in 18 of the 51 specimens (unilateral in 11 and bilateral in 7). M. pubo-ischio-femoralis is described as single-headed in Colaptes, but in 23 of our specimens there were two distinct bellies; in 9 this condition was unilateral and in 14 it was bilateral. In 35 of the 51 specimens, M. flexor perforatus digiti IV consisted of two heads. In 16 specimens the muscle had three heads, a condition only described in some procellariiform and galliform birds. This condition was bilateral in all 16 specimens. As possible explanations for these variants we consider atavism, adaptive variation, and random variation. We urge caution in characterizing picid species on the basis of these three muscles.