TIME-ENERGY USE AND LIFE HISTORY STRATEGIES 



147 



Table 2. Wing molt in alcids. After Stresemann and Stresemann (1966). 



Rapidity of wing molt 

 and (indented) flight 

 capability in molt Timing of start of molt Species 



Slow 

 Retained 



Retained 



Rapid 



Poor 

 Almost synchronous 



None 

 Synchronous 



None 



None 



During care of young 



After young become independent 

 After arrival in winter quarters 

 After end of breeding 

 As soon as young go to sea 



In winter, after body molt 



Cassin's auklet, parakeet auklet 



(Cyclorhynchus psittacula), 



whiskered auklet (Aethia pygmaea) 

 Least auklet (A. pusilla), crested 



auklet (A. cristatella) 

 Marbled murrelet, Kittlitz's murre- 



let (Brachyramphus brevirostris) 

 Xantus' murrelet (Endomychura 



hypoleuca) 

 Guillemots (Cepphus spp.), murres, 



razorbill (Alca torda), dovekie 



(Alle alle) 

 Puffins 



jury in migrating are less than in residency, 

 and so on. Interspecific and intraspecific com- 

 petition may also be involved (Cox 1968). In 

 other words, migratory patterns are selected 

 to optimize survival and reproduction in alter- 

 nating environments (Cohen 1967; Drury and 

 Nisbet 1972). 



Although one may suspect that location of 

 winter food supply is the main environmental 

 factor affecting migratory patterns, there is 

 little direct evidence on the reasons for, or the 

 benefits accruing from, the different patterns 

 seen in seabirds. Study of cost-benefit ratios 

 of foraging in different stages of migration 

 might help clarify the question. 



Molt 



Patterns of molt vary widely among sea- 

 birds. The commonest pattern is for a prenup- 

 tial body molt to occur in spring, and for an 

 extended wing molt to begin after the breed- 

 ing season and continue well into the winter 

 (Fig. 4). In short-distance migrants, molt may 

 overlap slightly with the end of breeding and 

 can last up to 6 months, as in most gulls, 

 terns, alcids, nonmigratory jaegers, and cor- 

 morants (Stresemann and Stresemann 1966). 



Long-distance migrants frequently delay 

 molt until in the winter quarters (lesser black- 

 backed gull, Lams fuscus; Sabine's gull; 

 jaegers; arctic tern, Sterna paradisaea; and 

 marbled murrelet, Brachyramphus mar- 



moratus) and molt there may occur rapidly 

 (3.5 months in the arctic tern). Certain other 

 long-distance migrants begin molt before 

 leaving the breeding grounds (herring gull; 

 skua, Catharacta skua; Leach's petrel, 

 Oceanodroma leucorhoa; and fulmar), al- 

 though molt may be interrupted during mi- 

 gration, as in Larus argentatus heuglini 

 (Stresemann and Stresemann 1966). Dura- 

 tion, timing, and rapidity of molt are particu- 

 larly varied among the alcids (Table 2). 



A few unusual molt patterns are found in 

 northern seabirds. The ivory gull (Pagophila 

 eburnea) has its major annual wing and body 

 molt immediately before it breeds. In several 

 other species such as the glaucous gull (Larus 

 hyperboreus) and Cassin's auklet (Ptychoram- 

 phus aleuticus) the molt almost completely 

 overlaps the reproductive cycle (Johnston 

 1961; Payne 1965). Potts (1971) documented a 

 molt pattern in shags (Phalacrocorax aristo- 

 telis) which is more typical of tropical sea- 

 birds. Several cycles of wing molt take place 

 simultaneously, each lasting more than a 

 year, and molt ceases in winter. By the time 

 breeding age is reached, each flight feather is 

 replaced once a year. 



Within these broad categories of molt pat- 

 tern there are sometimes variations according 

 to age, sex, and even subspecies (Stresemann 

 and Stresemann 1966). Male common eiders 

 (Somateria mollissima) molt directly after 

 mating, when their reproductive role is com- 

 pleted, whereas females molt only after they 



