148 



E. H. DUNN 



have taken their young to sea. Nonbreeders 

 and failed breeders frequently begin molt 

 while other adults are still raising young and 

 not molting e.g., many alcids, gulls, storm- 

 petrels, and fulmars (Stresemann and Strese- 

 mann 1966; Ingolfsson 1970; Harris 1971; 

 Harris 1974; Sealy 19756). In ivory gulls, 

 which molt just before reproduction, and in 

 Sabine's gulls, which complete molt just be- 

 fore breeding, nonbreeders may extend wing 

 feather growth into the breeding season 

 (Stresemann and Stresemann 1966). 



There is little information on the energetic 

 cost of molt, although there are indications of 

 at least some expense. Belopol'skii (1961) 

 showed that nonmolting seabird species 

 tended to gain weight after reproduction, 

 whereas those that immediately started molt 

 tended to lose weight. Among other birds, 

 however, it is common for individuals to gain 

 weight just before, and even during molt 

 (Payne 1972). The BMR is known to rise in 

 molting birds (Blackmore 1969; Lustick 1970; 

 Payne 1972), from as little as 5% to as much 

 as 34% above nonmolting levels. In one 

 study, about 35-40% of the increased BMR 

 represented extra thermoregulatory costs in- 

 curred by lessening of insulation and increase 

 in heat loss from well-vascularized new 

 feathers; the rest of the increase represented 

 the energetic cost of growing feathers (Gavri- 

 lov 1974). The fact that molt rarely overlaps 

 with breeding suggests that the energetic 

 cost, even if slight, may be incompatible with 

 the already high costs of reproduction (Payne 

 1972). Cassin's auklets, which do molt while 

 breeding, may cease molt while feeding large 

 young (Payne 1965), and certain species inter- 

 rupt molt during migration (Stresemann and 

 Stresemann 1966). Doubtless a rapid simul- 

 taneous molt is more costly than a long 

 gradual one. 



Rapid molt appears to occur at a time in the 

 annual cycle when food resources are abundant 

 (spring or late summer), whereas extended 

 molt generally occurs over winter (e.g., 

 Bedard 1969a). If one speculates that energy 

 availability is the main determinant of molt 

 patterns, one can also speculate on the cause 

 behind some of the more unusual patterns. 

 Possibly birds in which molt and breeding 

 overlap either have extraordinary available 

 energy at that time or else face shortages in 



other periods. For example, ivory gulls, which 

 breed in the high Arctic, molt when food re- 

 sources have become abundant in the low Arc- 

 tic but before the high Arctic breeding 

 grounds have thawed sufficiently for reoc- 

 cupation. 



Speed of molt may also reflect availability 

 of energy resources or of nutrients needed for 

 feather growth (Payne 1972), but must also be 

 influenced by the need for full flight capabili- 

 ties to obtain food. The eider duck and many 

 alcids that shed wing feathers almost simul- 

 taneously do not need their wings for flight 

 after the young have left the breeding colony. 

 Hydrodynamic considerations suggest that 

 their fishing capabilities may even be im- 

 proved (Storer 1960). This is not true for the 

 smaller species e.g., Aethia molts only one 

 feather at a time and retains full flight cap- 

 abilities (Table 2). Climate may also influence 

 simultaneity of molt if heat loss in rapid molt 

 is particularly severe. 



Reproduction 



Time use of seabirds is best known for the 

 reproductive period, when the birds are on 

 relatively accessible breeding grounds, the 

 weather is most suitable for observation, and 

 academic researchers are freed from their 

 jobs. Even so, the details of timing are known 

 for only a few of the species and localities on 

 the northwest North American coast (e.g., 

 Drent and Guiguet 1961; Drent et al. 1964; 

 Cody 1973; Sealy 1973a, 19756, 1975c). The 

 following discussion emphasizes the multi- 

 tude of environmental factors known to influ- 

 ence timing and total length of time devoted 

 to various aspects of the reproductive cycle. 



Timing of the Season 



Each species of seabird returns to the 

 colony site when weather conditions have 

 ameliorated sufficiently to meet its particular 

 needs. For example, the early arrivals to is- 

 lands in the Barents Sea are murres, kitti- 

 wakes, and herring gulls, which need only 

 small cracks in the sea ice to meet their feed- 

 ing requirements (Belopol'skii 1961). Eiders in 

 North America also return early, when a few 

 ice leads have formed (Schamel 1974). Com- 

 mon puffins (Fratercula arctica) and mew 



