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, Thickbilled 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 male 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. Received 12 February 1997, accepted 9 December 1997. RELATIVE TO MOST OTHER TOPICS in ornithology, virtually all aspects of the molting process are poorly documented and understood (Pyle et al. 1987, Jenni and Winkler 1994). This is especially true in seabirds because most species, including all species that become flightless during molt, undergo molt at sea during the nonbreeding season (Palmer 1962, Glutz von Blotzheim and Bauer 1982, Cramp 1977, 1983, Warham 1996). Among alcids, molt has been better studied in Common Murres (Uria aalge) than in many other species (Verwey 1922, 1924, Salomonsen 1944, Stresemann and Stresemann 1966, Birkhead and Taylor 1977), but many aspects of their molt remain poorly known (contra Harris and Wanless 1990). As an extension of studies on seabird entanglement in gill nets in Puget Sound (Thompson et al. 1998), we studied molt in Common 4E-mail: thompcwt@dfw.wa.gov Murres. The phenology of breeding in Common Murres differs by two months or more among geographic areas. Thus, flight-feather molt scores in postbreeding adults might be useful for identifying breeding location (e.g. Oregon vs. Washington); this is important for determining the demographic effect of mortality caused by gill nets or other anthropogenic activities on different breeding populations of Common Murres. MATERIALS AND METHODS In 1993, commercial gill net fisheries occurred for summer sockeye salmon (Onchorhynchus nerka) in northern Puget Sound and for fall chum salmon (0. keta) in Hood Canal and central Puget Sound, Washington (Pierce et al. 1994). To evaluate various modified gill net designs, test fisheries were done in 1993 by Washington Sea Grant, and in 1993 and 1996 by Washington Sea Grant and Washington Department of Fish and Wildlife. Entangled seabirds were collected: (1) from commercial fisheries in 1993 from 1