Carter and Stein 



Chapter 9 



Molts and Plumages 



in behavior and biology. Flightless murrelets must select 

 molting areas which provide adequate prey resources within 

 swimming distance for about two months. Clearly, it is 

 impossible for Marbled Murrelets to overlap breeding with 

 the flightless pre-basic molt because they would be unable to 

 fly to nests. In contrast, the gradually molting auklets retain 

 flight during the pre-basic molt and do overlap pre-basic 

 molt with breeding (Bedard and Sealy 1984, Emslie and 

 others 1990, Payne 1965). 



It is likely that the timing of molt varies between years 

 and between different parts of the breeding range, in concert 

 with variation in the timing of breeding and variation in 

 local prey resources (Ewins 1988, Emslie and others 1990). 

 It is clear that the hormonal integration of molt, breeding 

 and other aspects of the annual cycle of the Marbled Murrelet 

 is complex and our understanding of these processes is 

 limited. In southern parts of the breeding range in North 

 America where murrelets are largely resident, visitation of 

 nesting areas does not occur during the flightless pre-basic 

 molt, does occur during the winter period (when birds are in 

 basic plumage), is reduced during pre-alternate molt (prior 

 to egglaying), and then occurs throughout the breeding season 



by birds in alternate plumage (Carter and Sealy 1986, Naslund 

 1993b). Some birds that nest farther north in parts of British 

 Columbia and Alaska appear to winter in different areas or 

 habitats than where they breed. While a portion of the 

 population may visit nesting areas for most of the year, a 

 significant portion or the majority may visit nesting areas 

 only during the breeding season (Rodway and others 1992). 

 Such major differences in the annual cycles of differing 

 populations undoubtedly results in complex patterns of molts 

 and plumages in different geographic areas. 



Timing of Breeding and Pre-Basic Molt 



In Barkley Sound, British Columbia, Carter (1984) found 

 that the asynchronous or protracted timing of breeding within 

 this population of Marbled Murrelets appeared to lead to a 

 protracted pre-basic molt period (fig. 4). Breeding occurred 

 mainly from early April to the end of July, although it extended 

 as late as mid-September. The first fledglings were observed 

 on 4 July 1979 and 28 June 1980 and the last fledgling (a 

 recently-fledged juvenile with an egg tooth) was collected on 

 5 October 1980. The last bird in alternate plumage was 

 observed flying and carrying a fish on 17 September 1980. 



M 



M 



N 



Figure 4 Annual cycle of molts, plumages, breeding phenology and attendance of at-sea feeding areas 

 for Marbled Murrelets in southern Vancouver Island, British Columbia, in 1 979-1 980 (Carter 1 984; Carter, 

 unpubl. data; Sealy 1975b). Codes are: AHY (attendance by adult, after-hatching-year birds); IP 

 (incubation period); NP (nestling period); HY (attendance by juvenile, hatching-year birds); BP (basic 

 plumage); PAM (pre-alternate molt); AP (alternate plumage); PBM (pre-basic molt); WM (wing primary 

 molt); RFJ (recently-fledged juvenile); and OJ (older juvenile). Thick portions of ranges indicate timing for 

 a large proportion of the population. Thin lines indicate usual range. Dots indicate extremes. 



104 



USDA Forest Service Gen. Tech. Rep. PSW-152. 1995. 



