Carter and Stein 



Chapter 9 



Molts and Plumages 



I Ye- Basic Molt Duration and Sequence 



The length of time required to complete the pre-basic 

 molt is not well known because individuals have not been 

 followed in captivity or in the wild throughout this period. In 

 Barkley Sound, British Columbia, Carter (unpubl. data) 

 determined that the relatively synchronous molt of the 

 primaries, secondaries and rectrices in each individual required 

 about 65 days but ranged between 45 and 75 days, based on 

 a regression of molt scores and date (Pimm 1 976). The entire 

 pre-basic molt (body and remiges) probably requires about 

 2-3 months per individual. In adult birds, pre-basic molt 

 occurs almost simultaneously in all body tracts. Body molt 

 begins slightly before and ends slightly after remigial molt. 

 In the field, body molt is visible first in the throat area, as the 

 dark feathers are lost and replaced with white feathers. The 

 completion of body molt proceeds from anterior to posterior 

 in ventral feather tracts from the breast to the vent area. In 

 some ventral areas, thick dark-margined feathers are not all 

 lost simultaneously and some are retained for a period of 

 time. Remnant feathers from the alternate plumage were 

 visible mainly in abdominal areas on museum specimens we 

 examined as late as December. The grey-edged, dark back 

 feathers (typical of the basic plumage) gradually replace the 

 rust-edged feathers as the molt progresses. Certain museum 

 specimens that had not yet shed their primaries already 

 showed some grey-edged back feathers, suggesting that molt 

 starts earlier in this region. 



During pre-basic molt, murrelets are flightless (Carter 

 1984), as is expected during a synchronous wing molt. Such 

 molts are considered to be adaptive by shortening the period 



of feather replacement in birds with aerodynamically 

 inefficient wings such as loons (Savile 1957, Woolfenden 

 1967), alcids, and diving petrels (Storer 1971, Stresemann 

 and Stresemann 1966, Watson 1968). Stresemann and 

 Stresemann (1966) considered the Marbled Murrelet to have 

 an "accelerated" pre-basic molt where they incorrectly 

 assumed that birds could barely fly during molt. Whereas 

 murrelets are in fact flightless, they do have a less than 

 synchronous pattern of primary replacement. Carter (unpubl. 

 data) found that the first six primaries are lost in order and 

 almost simultaneously; the outer four primaries are lost later. 

 The order of feather loss and replacement is similar to gradual 

 molting auklets and to most birds. The delay in the molt of 

 the outer primaries also was evident in birds examined by 

 Stresemann and Stresemann (1966). Eventually, all primaries 

 are shed and growing at the same time. However, due to the 

 delay in the shedding of the outer primaries, the growth of 

 the inner primaries are completed first, leading to a rounded 

 wing tip in birds later in the molt (fig. 5). Regardless of the 

 delay in the outer primaries, pre-basic molt still occurs 

 relatively rapidly. Molt duration is similar to Common Murres, 

 Uria aalge (mean = 63 days in nine captive birds; Birkhead 

 and Taylor 1977) but takes longer than for ducks (e.g., 18-29 

 days; Bailey 1980, Balat 1970). 



Pre-Alternate Molt Duration and Sequence 



The duration and sequence of pre-alternate molt is even 

 less well known. It is likely that this molt occurs more 

 rapidly than the pre-basic molt. Carter and Erickson (1988, 

 1992) noted that museum specimens from California collected 



HY Non-Molting Juvenal Plumage 



Figure 5 Wing tracings of juvenile, hatching-year (HY) and adult, after-hatching-year (AHY) Marbled Murrelets, illustrating differences 

 between non-molting and molting birds. Molting adult birds have "stubby" wings (bottom right) if all primaries have been recently lost, 

 or "paddle-shaped" wings (top right) as the new inner primaries grow out before the outer primaries. All birds were collected on 1 

 September 1992 in Mitrofania Bay, Alaska by J. Pitocchelli. Tracings by H.R. Carter. 



106 



USD \ Forest Service Gen. Tech. Rep. PS W- 152. 1995. 



