The Condor 90:220-227 0 The Cooper Ornithological Society 1988 STEPWISE MOLT OF REMIGES IN BLUE-EYED AND KING SHAGS PAMELA C. RASMUSSEN Museumof Natural Historyand Departmentof Systematicsand Ecology, Universityof Kansas,Lawrence, KS 66045 Abstract. In Blue-eyed and King shags(Phalacrocorax atriceps and P. albiventer),the first prebasic molt of the primaries begins at Pl and proceedsdistally. Continual stepwise molt of the primaries begins with commencement of PB2 after replacement of P5 to P8 by the first prebasic molt. Adults had from one to four concurrent distally moving waves of molt in primaries. In secondariesof these species,the first prebasicmolt beginsperipherally at S 1 and S 15 and proceeds centrally. The second prebasic molt then begins peripherally before the central secondariesare replaced by PB 1. Secondariesof adults’ are molted by up to six concurrent waves that originate peripherally; I term this bidirectional stepwisemolt of secondaries.Stepwise molt tends to be asymmetrical both in adults and subadults.Sub- adults of these specieshave more molting feathers per wave in primaries and secondaries than do adults, but the age classesdo not differ in number of molting feathers per wing. Molt of remiges in subadultsinitially resemblesthe condition in the Procellariiformes, the nearest outgroup,while the stepwisemolt of adults is synapomorphicfor Pelecanifonnes. Key words: Blue-eyedShag; King Shag;Phalacrocorax atriceps; Phalacrocorax albiven- ter; molt. INTRODUCTION eventually reachesthe wing tip (Ashmole 1968) Although the wing molts of cormorants (Phala- but not during the year in which the wave began crocoracidae) are highly complex and unusual, (at least not in the Masked Booby, Sula dacty- detailed information on molts of primaries in lutru, Dorward 1962; or the European Shag,Potts this cosmopolitan family is available only for the 197 1). Each wave probably continuesfrom where European Shag (Phalacrocorax aristotelis; Potts it paused; primaries are replaced once per year 197 1). All speciesof Pelecaniformes studied thus or less in the Masked Booby (Dorward 1962). far have shown stepwise molt (called “Stajd- The other known type of stepwisemolt is “per- nz2iuser”by Stresemann and Stresemann 1966, iodic stepwise molt” (Stresemann and Strese- and “serially descendent molt” by Ginn and mann 1966) in which successivewaves begin at Melville 1983) of the primaries (Dorward 1962, the innermost primary, but only one of every Potts 1971, Berry 1976, DeKorte and DeVries two, or two of three waves reach the wing tip. A 1978, Bernstein and Maxson 198 1, Crawford et variable number of the outermost primaries are al. 1982, Ginn and Melville 1983, Cooper 1985, thus molted less frequently than the innermost, Rasmussen 1987). However, very little is known although every primary is molted at least once concerning the ontogeny and mode of progres- yearly. Periodic stepwisemolt is known only in sion of stepwise molt in primaries. In stepwise some terns of the genus Sterna (Stresemann and molt of primaries, a molt wave begins at a certain Stresemann 1966). point (in most speciesPrimary 1 [Pl]) before the The molt of secondariesin Pelecaniformes has previous wave, which originated at the same been virtually ignored; published data on molt point, is completed, thus there is more than one patterns of secondaries in members of this di- concurrent, overlapping molt wave (seeFigs. 1A, verse order exist only for the Rock Shag (P. ma- B). “Continual stepwise molt” occurs in Pele- gellanicus;Rasmussen 1987). Few data have been caniformes and a few other birds (Stresemann published on molts of the Blue-eyed Shag and and Stresemann 1966); in this type of stepwise the King Shag morph (P. atriceps and P. “albi- molt successivewaves begin at Pl. Each wave venter”; Watson 1975, Bernstein and Maxson 1981). In the Antarctic Blue-eyed Shag (P. atri- ceps bransfieldensis)molt of flight feathers ap- I Received15 June 1987. Final acceptance2 October pearsirregular, with no obvious orderly sequence 1987. of molt (Bernstein and Maxson 198 1). VW MOLT OF SHAGS 221 IIIIII 111 11 II 11 1 II 11 1 I u 52-c (n +3) - 2 (n t-2) ____-__ g I -- (nt I) __-___..__-_* I I I I I I I I II I I$ (n) -__--________ _____c 12345678910 Proximal Distal Illllrlllll Primaries 12345678910 Proximal Distal Primaries FIGURE 1. Stepwisemolt of primaries. Arrows indicate apparent direction and extent of wave progression; dashed portions of arrows indicate feathers of that round presumed replaced by later round(s). (A) Subadult King Shag, YPM 82275: commencement of stepwise molt. (B) Adult Blue-eyed Shag, AMNH 443237; four- round stepwisemolt. In this paper I document the ontogeny of step- sultsin remigesof varying agesthat are not readi- wise molt of the remiges in Blue-eyed and King ly classifiableas “new” or “old” (pers. observ.); shags,and describe and compare characteristics for this reason I did not use Ashmole’s (1962) of continual stepwisemolt of primaries and bi- standard molt scoring system. directional stepwise molt of the secondaries in these cormorants. TABLE 1. Number of specimens of Blue-eyed and Ring shagsexamined for each season,age class, geo- METHODS graphic region, and specimen nature. I categorizedspecimens in first prebasic molt as BILE subadults, and those that had molted all juvenal eyed King feathers as adults. Total numbers and nature of Shag Shag specimens examined for each season, age class, Season and geographic region are given in Table 1. Winter (Jun-Aug) 4 9 Eighty-five (88%) of the 97 Blue-eyed Shag spec- Spring (Sep-Nov) 10 10 imens examined were molting; 49 (72%) of the Summer (Dee-Feb) 60 39 23 10 68 King Shagswere molting. Fall (Mar-May) Primaries (excluding the remicle, Pll) were Age classes numbered Pl to PlO from the carpal joint dis- Juveniles 14 17 Subadults 33 tally, and secondariesS 1 to S 15 (in two casesto Adults 50 :: S17) from the carpal joint to the humero-ulnar joint. Molt data were taken from all remigeswhen Geographicregion Southern South America 51 48 possible. Each remex was assignedto an age cat- Falkland Islands 0 15 egory O-10 (1-5 are also growth categories):(0) South Georgia Island 10 0 juvenal; (1) missing; (2) new feather just visible; Shag Rocks (50”33’S, 42”02’W) 1 0 (3) less than ‘/4 grown; (4) l/4 to % grown; (5) South Shetland Islands 17 0 Antarctic Peninsula 18 0 greater than % to not quite fully grown; (6) full- Macquarie Island 0 5 length, no wear or fading; (7) very slight wear and/or fading; (8) light but obvious wear and Specimen nature fading; (9) moderate wear and fading; ( 10) heavy Museum skin 70 60 Freshly-killed 27 8 wear and fading. This system reduces error due Totals 97 68 to the extended molt of cormorants, which re- 222 PAMELA C. RASMUSSEN To determine whether the first prebasic molt Shags, PB2 had not yet begun by the time P7 (PB 1) of primaries or of secondariescommenced was replaced by PB 1. In subadult King Shagsin first, and whether in the secondaries PBl first which PB2 had begun, PB2 started when juvenal commenced distally or proximally, I assumed P6 (n = 1) and P7 (n = 1) had been replaced by that all secondaries and the primaries grow at PB 1. The beginning of PB2 marks the onset of approximately equal rates (as primaries appar- stepwise molt, because from that point on PBl ently do in the Masked Booby, Dorward 1962; and PB2 continue simultaneously (Fig. 1A). and in the Great Cormorant [P. C&JO] and Eu- In most cases,juvenal primaries were replaced ropean Shag, Ginn and Melville 1983). sequentially, with PI0 the last to be replaced. I considered molt of remiges symmetrical if However, omissive molt (Cannel1 et al. 1983) feathers of each bilateral pair (L5, R5) were in occurred occasionally; in one Blue-eyed Shag, the same age category or were molting simulta- juvenal P8 and P9 were retained on both wings neously. Symmetry of remiges was expressedas after PI0 had been replaced, and in another ju- the percent of individuals examined with com- venal P7 and P8 were retained on one wing and pletely symmetrical molt. juvenal P7 on the other after more distal pri- A “molt cycle” is the period from the begin- maries had been replaced. In the King Shag,ju- ning of one molt to the beginning of the next venal P6 was retained on both wings of one spec- homologous molt (Humphrey and Parkes 1959). imen, juvenal P7 on both wings of another, and Becausein stepwise molt homologous molts of juvenal P6 on one wing and P8 on the other wing remiges overlap temporally, I use the term of a third, all after more distal primaries had been “round” for the complete replacement of a feath- replaced. er row by one unidirectional wave (as in pri- Adults of both morphs showed stepwisemolt maries), or by two waves that begin more or less of primaries from proximal to distal (Fig. 1B). simultaneously distally and proximally (as in sec- From zero to four waves occurred in primaries ondaries); one round is thus the replacement of of each wing in adults of both morphs (Fig. 2). all feathers of a feather row (whether primaries In 46 adult Blue-eyed Shags, x = 1.93 -t 1.12 or secondaries)by one molt cycle. A “molt wave waves per wing, and in 3 1 adult King ShagsK = front” is the most recently molted feather in a 2.39 f 0.88 waves per wing. series of feathers of decreasing age (of a single Subadult Blue-eyed Shags had significantly wave of molt). The number of molt waves in more primaries molting per molting wave than remiges of each wing equals the number of wave did adults (Table 2).