Carter and Stein 



Chapter 9 



Molts and Plumages 



should be considered to be a separate species (Friesen and 

 others 1994a, Piatt and others 1994). 



Nestling Plumage 



Binford and others (1975) described the downy chick in 

 detail. Newly-hatched chicks are covered by a thick layer of 

 natal down. Generally, the yellowish down is interspersed 

 with irregular dark spots that cover the upper parts and are 

 more prevalent on the head. A paler grey down covers the 

 belly (Simons 1980). The down covers the developing Juvenal 

 plumage and is retained for a relatively long period of time, 

 until just prior to fledging. At this time, the down appears to 

 be preened or scratched off and may be ingested by the chick 

 (Simons 1980). At fledging, juvenile birds fly to the ocean 

 (Carter and Sealy 1987b, Hamer and Cummins 1991). Most 

 juveniles arrive at sea in juvenal plumage, although some 

 individuals may still retain some down, especially on the 

 neck and crown (Sealy 1975a). 



The cryptic downy nestling plumage of the Marbled 

 Murrelet is also an obvious adaptation for nesting in old- 

 growth forests (Binford and others 1975) or on mountainous 

 scree slopes. Chicks of precocial alcids have more dense 

 down coverings and resemble the adult plumage in pattern 

 and coloration. Other semi-precocial alcid nestlings (like the 

 Marbled Murrelet) have unmarked grey down. The late 

 retention of this downy nestling plumage, in association 

 with nest placement, tree bark or rock color, adult activities, 

 and chick behavior, is probably important for reducing 

 predation at the nest site. 



Juvenal Plumage 



Recently-fledged juveniles are uniformly dark brownish 

 above with white scapulars. The underparts and sides of the 

 head are white and speckled with blackish brown which 

 does not fully conceal the white ground color of the feathers 

 (fig. 3). The under wing coverts are brownish grey with 

 some white. White bars are present on the outer rectrices and 

 the inner vanes are pale brownish. Recently-fledged juveniles 

 also retain the egg tooth for some time after fledging (Sealy 

 1970), although it is almost impossible to see the egg tooth 

 in the field. The late retention of the egg tooth is probably 

 related to the late retention of nestling down, early fledging 

 (i.e. when less than fully grown), or both. 



The juvenal plumage of recently-fledged juveniles differs 

 from older juveniles that have been at sea for a longer period 

 of time. Recently-fledged juveniles appear darker overall 

 with most feathers on the sides of the head, neck, breast and 

 abdomen edged with thin dark margins (fig. 3). This pattern 

 gives juveniles a "speckled" appearance, especially on the 

 breast and upper abdomen. Thicker dark margins occur on 

 the side and flank feathers (similar to adults). Recently- 

 fledged juveniles often exhibit a neckband formed by a 

 greater density of feathers with dark margins in the upper 

 breast region. The plumage of recently-fledged juveniles is 

 often referred to as the "juvenal plumage" in such field 

 identification guides as the National Geographic Society 



guide (1983). Older juveniles appear to become whiter and 

 lose any neck band and most or all of the dark margins that 

 characterize typical juvenal plumage (fig. 1). This transition 

 may occur as early as a few weeks after fledging. In addition, 

 the uniform dark brown to black feathers on the upperparts 

 of recently-fledged juveniles are replaced with feathers edged 

 with thick grey margins in older juveniles (similar to adult 

 birds). It is unclear how these plumage changes occur during 

 this period (see below). Once older juveniles have completed 

 this plumage transition, they are impossible to separate from 

 adult birds in full basic plumage in the field (fig. 1). However, 

 in the hand, remnant speckling of the juvenal plumage can 

 be seen on the ventral parts of some birds as late as February. 

 One hypothesis that explains the plumage transition 

 between recently-fledged and older juveniles is that murrelets 

 have not achieved their full juvenal plumage at fledging. 

 Chicks fledge at 70 percent adult weight (Sealy 1975a) and 

 grow to attain full adult size at sea. For instance, recently- 

 fledged juveniles often still have sheathed outer primaries. 

 The dark margins on recently-fledged juveniles may represent 

 a stage of feather growth between the shedding of natal 

 down and the full attainment of juvenal plumage when full 

 adult size is reached. The dark-margined ventral feathers 

 and/or the grey back feathers may be replaced near the end 

 of the "nestling" growth period that occurs at sea. 

 Alternatively, the thin and fragile dark margins of the ventral 

 feathers may wear off quickly when exposed to salt water 

 and swimming and diving activities. A second explanation 

 for the plumage transition between recently-fledged and 

 older juveniles is that a separate partial body molt occurs, 

 causing loss and replacement of dark-margined ventral feathers 

 and dark back feathers with completely white and grey- 

 margined feathers, respectively. Kozlova (1957) stated that 

 the juvenal plumage is exchanged for the first winter plumage 

 in the fall. She did not provide the basis for this statement, 

 and it is unclear if actively molting feather tracts were observed 

 on specimens examined. If such a molt did occur, it would 

 probably occur some time well after fledging. We cannot 

 currently determine which mechanism best explains this 

 transition because the actual fledging dates of specimens 

 examined is not known and could vary by several months 

 due to protracted breeding. Some form of feather replacement 

 could be supported by finding actively molting feather tracts 

 on juveniles collected in late summer and early fall. 



Annual Cycle of Molts and Plumages 



Pre-alternate and pre-basic molts are controlled by levels 

 of sex and other hormones, which change throughout the 

 year. The pre-alternate molt precedes breeding and is 

 associated with egg-laying and/or associated nesting behaviors. 

 However, the onset and progression of molt probably also is 

 modified by several environmental factors. Molt imposes 

 high energetic demands within the annual cycle of the Marbled 

 Murrelet. In particular, the replacement of flight and body 

 feathers during the pre-basic molt requires significant changes 



102 



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



