An unusual sequence of flight-feather molt in common murres and its evolutionary implications

Abstract

Common Murres (Uria aalge) exhibit an unusual molt sequence. Primary molt begins at a focus between P4 and P7 and progresses in two rapid concurrent waves, proximally to P1, and distally to P10. The only other birds known to have a similar molt sequence are caracaras and falcons (Falconidae), parrots (Psittaciformes), and Pied Kingfishers (Ceryle rudis). Great Auks (Pinguinus impennis) also appear to have followed the same primary-molt sequence. Phylogenies for the Alcidae indicate that Great Auks, Common Murres, Thick-billed Murres (Uria lomvia), Razorbills (Alca torda), and Dovekies (Alle alle) share a common ancestor and are more closely related to one another than to other alcids. This suggests that the unusual sequence of primary molt in Common Murres is a shared-derived character that occurs in the other four species in their clade but has been overlooked. Adult mate Common Murres have significantly shorter secondaries and longer primaries, on average, than do adult females, resulting in a slightly higher aspect ratio in males. Secondary molt begins when primary molt is more than one-third completed. Secondaries are replaced rapidly but sequentially (not synchronously or simultaneously); molt appears to proceed from two foci, proximally from S1 to S4, and both proximally and distally from S8, but more data are needed to clarify this point. Rectrix molt begins when primary molt is two-thirds completed. Rectrix loss and replacement occur rapidly, possibly synchronously, and in no apparent order. Adults molt about two weeks later than nonbreeding subadults. We found no differences in the timing of molt between the sexes in adults or subadults. Duration of flight-feather molt can vary from less than 25 days to more than 80 days, possibly reflecting interyear variation in prey abundance.