AN UNUSUAL SEQUENCE OF FLIGHT-FEATHER MOLT IN COMMON MURRES AND ITS EVOLUTIONARY IMPLICATIONS

Common Murres (Uria aalge) exhibit an unusual molt sequence. Primary m olt begins at a focus between P4 and P7 and progresses in two rapid co ncurrent 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 r udis). Great Auks (Pinguinus impennis) also appear to have followed th e same primary-molt sequence. Phylogenies for the Alcidae indicate tha t Great Auks, Common Murres, Thick-billed Murres (Uria lomvia), Razorb ills (Alca torda), and Dovekies (Alle alle) share a common ancestor an d are more closely related to one another than to other alcids. This s uggests that the unusual sequence of primary molt in Common Murres is a shared-derived character that occurs in the other four species in th eir clade but has been overlooked. Adult male Common Murres have signi ficantly 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 complet ed. Secondaries are replaced rapidly but sequentially (not synchronous ly or simultaneously); molt appears to proceed from two foci, proximal ly from S1 to S4, and both proximally and distally from Sg, but more d ata are needed to clarify this point. Rectrix molt begins when primary molt is two-thirds completed. Rectrix loss and replacement occur rapi dly, possibly synchronously, and in no apparent order. Adults molt abo ut two weeks later than nonbreeding subadults. We found no differences in the timing of molt between the sexes in adults or subadults. Durat ion of night-feather molt can vary from less than 25 days to more than 80 days, possibly reflecting interyear variation in prey abundance.