Carter and Stein 



Chapter 9 



Molts and Plumages 



as early as 1 8 February already had some white body feathers 

 with broad dark margins on their underparts (fig. 2). It is not 

 likely that these represent remnant feathers that were not 

 replaced during pre-basic molt because several specimens 

 exhibited a similar pattern in late February. By March, many 

 specimens were well into alternate plumage. The first bird in 

 full alternate plumage was collected on 26 March, as were 

 several birds on the same date. Without further information, 

 pre-alternate molt appears to occur rapidly and requires 

 about one month. Additional field work and examination of 

 more specimens will better establish the full sequence of the 

 pre-alternate body molt. However, the highest density of 

 dark, thick-margined feathers were seen in the neck area on 

 several spring specimens, suggesting that molt proceeds 

 from anterior to posterior in the ventral tracts. 



Behavior and Diet of Murrelets During 

 Pre-Basic Molt 



In Barkley Sound, British Co'.imbia, Carter (1984) noted 

 that most adult birds departed f.orp the Sound after breeding 

 in early August (fig. 4) and presumably underwent the pre- 

 basic molt elsewhere. However, the smaller numbers of 

 adult birds that remained, moved into nearshore areas and 

 underwent molt from late July to November. During this 

 period, they occurred with juvenile birds which also did not 

 appear to leave the Sound until at least early October. Even 

 the smaller numbers of remaining adult and juvenile birds 

 were mostly gone by late December 1979 (Carter, unpubl. 

 data). Stresemann and Stresemann (1966) asserted that 

 Marbled Murrelets molt after reaching their wintering areas. 

 We presume that they reached this conclusion after examining 

 molting birds from California where, at that time, murrelets 

 were not known to breed. Undoubtedly, the proportion of 

 birds that remain to molt near breeding areas rather than 

 molt at wintering areas will depend on a variety of factors, 

 including the timing of breeding, degree of winter residency, 

 the timing of winter dispersal or migration, and other 

 environmental parameters. McAllister (pers. comm.) reported 

 that most adult birds remained in the general vicinity of 

 summer feeding areas in southeastern Alaska but tended to 

 occur in somewhat different areas and closer to shore during 

 molt in September. 



In Barkley Sound, flock sizes of adult birds during pre- 

 basic molt were difficult to obtain since few birds were 

 present and it was difficult to separate molting and juvenile 

 birds from a distance (Carter, unpubl. data). There were 30 

 flocks from which molting birds were collected in 1979- 

 1980. Of these flocks, 10, 15, 2, 2 and 1 contained 1, 2, 3, 5 

 and 6 birds, respectively. The larger flocks also contained 

 juveniles. McAllister (pers. comm.) noted the tendency for 

 juveniles to occur very close to shore in southeastern Alaska, 

 although he found juveniles in different areas than molting 

 adults. Most molting and juvenile birds were observed very 

 close to shore, usually within 200 m, in Barkley Sound 

 (Carter, unpubl. data). Most birds were observed in the Deer 



Group islands (south of Fleming Island, mainly in Satellite 

 Passage and near Seppings Island) and in the Broken Group 

 islands (Sechart Channel, Coaster Channel and between 

 Gibraltar and Nettle islands) (Carter, unpubl. data). In contrast, 

 birds were found both in nearshore, inshore and offshore 

 habitats in many parts of the Sound during the breeding 

 season (Carter 1984, Sealy and Carter 1984). One adult bird 

 that was collected on 24 July 1980 about 1.5 km SE of Cree 

 Island was just beginning primary molt. Birds must swim 

 into nearshore areas if they become flightless farther offshore. 



Carter (unpubl. data) collected five pairs of molting 

 Marbled Murrelets in Barkley Sound in the pre-basic molt 

 period. All were male-female pairs and were probably mated. 

 One pair had started body molt but not wing molt and the rest 

 were all actively undergoing wing molt. All mates were almost 

 synchronized and had very similar molt scores, despite the 

 generally asynchronous timing of molt within the population. 



During molt in Barkley Sound, adult and juvenile 

 murrelets fed primarily on small fish of size classes n and IE 

 (fish length classes: I, <30 mm; n, 30-60 mm; and HI, 60- 

 90 mm), primarily Pacific Herring (Clupea harengus), Pacific 

 Sand lance (Ammodytes hexapterus) and Northern Anchovy 

 (Engraulis mordax) (Carter 1984). On average, similar size 

 classes (n and HI) were eaten by wintering birds in December, 

 but smaller size classes (I and JJ) of the same species were 

 eaten by adults during the main breeding season. 



Guide for Differentiating Juvenile 

 Murrelets from Adult Birds at Sea in 

 Late Summer and Early Fall 



It is not difficult to differentiate a recently-fledged 

 juvenile from an adult bird at sea in alternate or basic plumage, 

 given adequate viewing conditions. Due to the protracted 

 breeding season, however, many complete or partial plumages 

 of both juveniles and adult murrelets may be encountered at 

 sea during the late breeding and early post-breeding seasons. 

 As mentioned previously, many factors affect counts of 

 juveniles at sea during this time, including timing of fledging, 

 at-sea mortality after fledging, timing of post-breeding 

 dispersal and ocean habitats used. Highest counts will occur 

 in suitable habitats in the post-breeding season when most or 

 all juveniles have fledged but have not yet dispersed. However, 

 during this period, confusion in identification occurs because 

 adult birds undergoing pre-basic molt become difficult to 

 separate from juveniles. In addition, older juveniles attain a 

 first-winter plumage that is inseparable in the field from 

 adult birds in basic plumage. Despite the difficulties of 

 determining breeding success indirectly from surveys of 

 juveniles at sea, such surveys are still one of the only measures 

 of breeding success, unless larger numbers of nests can be 

 located and monitored. 



To help prevent misidentification of juveniles at sea, 

 Stein and Carter (1994) examined museum specimens and 

 reviewed literature and unpublished data from British 

 Columbia, Washington, and California in order to evaluate 



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



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