Incomplete Flight Feather Molt and Age in Certain North American Non-Passerines
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Incomplete Flight Feather Molt and Age in Certain North American Non-passerines Peter Pyle Point Reyes Bird Observatory 4990 Shoreline Highway SUnson Beach CA 94970 ABSTRACT INTRODUCTION Based on specimen examination, informationis The timing,location and extentof moltsin North presented on incomplete or arrested prebasic Americanbirds are remarkablyunderstudied, given flight-feather molts, and differences between their basic importanceto avian biology(Rohwer juvenal and adult flight feathers, in North Ameri- andManning 1990, Thompson and Leu 1994). This can pigeons,doves (Columbidae),cuckoos, road- especiallyseems true of the "near-passerines" runners, anis (Cuculidae), nightjars (Capri- (dovesthrough woodpeckers in the sequenceof mulgidae), swifts (Apodidae), trogons the American Ornithologist's Union checklist (Trogonidae),and kingfishers(AIcedinidae). Indi- [1983]).Generally it has been assumedthat re- vidualsof mostof these familiesregularly (but not placementof flightfeathers (here definedas the always) retain flight-feathersfor one or more an- primaries,primary coverts, secondaries, and rec- nual cycles,until a subsequentprebasic molt. Re- trices)in these families,whether it occursduring tained flightfeathers most often includethe outer the first or the adult prebasic molt, is complete secondaries,although in some familiesor species, (Forbush1927, Bent 1932-1940, Roberts1955, primaries, primary coverts and/or rectrices may Wood 1969, Oberholser1974). But in many near- also be retained. In certain families or species passerinesthese moltsare incomplete,with one (groupA) flightfeathers are typicallyreplaced dur- to manyflight feathers, especially among the sec- ing the first prebasic molt, juvenal feathers being ondariesand primarycoverts, typically retained retained until the second prebasic molt, whereas through one or more molt cycles (Test 1945, in others (group B) flightfeathers are not typically Rohwer1971, Forsman1981, Cramp 1985, Evans replaced until the second prebasic molt, juvenal and Rosenfield1987, Baker 1993). Whilesporadic feathersbeing retained until the thirdprebasic molt. informationexists on retainedflight feathers in a In both of these groupsadult featherscan also be few species, especially in Europe, molt in most (but are not always) retained during subsequent NorthAmerican near-passerines has receivedlittle prebasicmolts. Four flight-feather patterns are thus or no attention since that of the earlier, general found in non-moltingbirds: uniformjuvenal, uni- works. form adult, mixed adult and juvenal, and mixed re- placedand retainedadult feathers. Assuming that While examiningmuseum specimens for informa- retainedjuvenal and adult feathers can be distin- tion on molt and ageing criteria, I foundthat indi- guished,many birdsof group A (pigeons,doves, viduals of most near-passerinespecies retained cuckoos,roadrunners and anis) can be reliably flight feathers regularly for more than one year, aged throughat least theirsecond year, and many and that retention patterns and differences be- birdsof group B (nightjars,trogons and the larger tweenjuvenal and "adult"(definitive or non-juvenal) kingfishers)can be agedthough at leasttheir third featherscould be used to reliablyage these indi- year. viduals, in some cases up to their third or fourth year of life. Jan.-Mar. North American Bird Bander .Page 15 The variablemolts and complexageing criteriaof RESULTS AND DISCUSSION owls, hummingbirds,and woodpeckerswill be de- tailedelsewhere. Here I summarizefindings in the Near-passerinesappear to have a single annual other NorthAmerican near-passerine families. molt that can occur on the summer grounds, the winter grounds,or both. Individualsof most spe- METHODS cies follow the same general sequence of flight- featherreplacement. Except in hummingbirds(Pyle Specimenshoused at the CaliforniaAcademy of et al. manuscript),and cuckoos and kingfishers Sciences(CAS), San Francisco,Museum of Ver- (see below), molt of the primariesstarts with the tebrate Zoology (MVZ), University of California, innermost,pl, and continuesdistally to the outer- Berkeley, and Point Reyes Bird Observatory most,p10. Primary-covertreplacement in all fami- (PRBO), Stinson Beach, California, were exam- lies exceptwoodpeckers (see Pyle and Howell in ined. On each specimen the flight feathers were press) and kingfishers(see below) usually corre- carefullystudied (see Rohwer 1971) for evidence spondswith that of the primaries.Replacement of of incompletereplacement or for differencesin the secondaries typically proceeds both distally colorpattern, shape and/or wear betweenjuvenal fromthe innermost("tertials") and, a bit later,proxi- and adult feathers. Birds that were collected in ac- mally from the outermost (sl) such that the last tive molt were noted, and for other specimensall secondariesreplaced are often amongs2-s7 (typi- retainedflight feathers were recordedby position cally,s3-s4). Replacementof the rectricescan be in the wing or tail. variable and often proceeds irregularly,finishing with feathers among r2-r4. In many species the Specimenswere assignedage codesfollowing the sequenceof replacementcan be protractedand/ calendar-basedsystem of the Bird BandingLabo- or suspended(see below)during migration or win- ratory(Canadian Wildlife Service [CWS] and U.S. ter, not being completeduntil spring. Fish and WildlifeService [FWS] 1991). Codes in- cluded: U/AHY for a bird of unknownage; HY/SY Retentionof flight feathers resultswhen the molt and AHY/ASY for birds in and beyond their first sequence does not complete before the next an- basicplumage, respectively; and SY/TY andASY/ nual cycle, unmolted feathers being held at least ATY for birds in and beyond their 2nd basic plum- untilcommencement of the next prebasicmolt. This age. In each case the codes representbirds in the has been termed an "arrested"or "abridged"molt one-year period between completionof molts(of- (see Ginn and Melville 1983, Norman 1991); as ten October to September);the code before the opposed to "suspended"molt, in which replace- slash applies until the end of the calendar year ment resumesafter migrationor winter but before (31 December) and the code after the slash ap- the next molt cycle. Thus, during the first flight- plies between thebeginning of the year (1 Janu- feathermolt, retained juvenal feathers often include ary) and the next molt. Primaries(p1-p10) and rec- the outermostprimaries, secondaries among s2- trices (rl-r6) were numbered distally (outward or s7, and/or rectricesamong r2-r4. Juvenal feath- away from the body) and secondaries (sl-s12) ers are usuallyretained symmetrically in bothwings proximally(inward or towardthe body). and both sides of the tail, or at most differ by one or twofeathers. These juvenal feathers may or may Terminologyof molt, plumagesand feather gen- not be the first replacedduring the next molt (see erationsfollows Humphrey and Parkes (1959; see Baker 1993: 23-24); as a consequence,molt se- also Thompsonand Leu 1994). Generationsof quences in adults can be irregular and retained feathersand plumagessubsequent to fledgingare feathersare less-oftensymmetrical. Both juvenal termed juvenal, 1st basic, 2nd basic, etc., while and adult flight feathers may or may not be re- adult feathers, plumagesand birds refer to those tained, hence four molt-retentionpattern catego- that are at least 1st basic in age (i.e., are not ries can be defined: uniform juvenal feathers, juvenal),but otherwiseare of unknownage. mixed juvenal and adult feathers, uniform adult feathers,and mixed replacedand retaineddefini- tive feathers(Figure 1). Page 16 North American Bird Bander Vol. 20 No. 1 A C D, Figure1. Generalizedrepresentation of fourretention patterns found in secondariesof near-passerines uniformjuvenal feathem (A), uniformadult feathem (B), mixedadult and juvenal feathem (C), and mixed replacedand retainedadult feathem (D). Note that juvenalsecondaries usually differ from those of adultsin beingnarrower, more tapered at the tip,and contrastingmore markedly in colorand wear with replacedfeathers, while retained adult feathem contrast less with replaced feathem. Retained juvenal feathemusually occur among s2-s7 and are oftenconsecutive and symmetricalin bothwings, whereas retainedadult secondaries can occurthroughout the wing,are oftennot consecutive,and are less fre- quentlysymmetrical in bothwings. North American pigeons, doves, cuckoos, roadrunners, and aniscan be agedHY/SY (patterns A andC), U/AHY(B), or AHY/ASY (D); while North American nightjars, trogons and Beltedand Ringedkingfishers can be agedHY/SY (A), AHY/ASY (B), SY/TY(C), or ASY/ATY(D). See text for more details. Jan.-Mar. North American Bird Bander Page 17 Assumingthat juvenal and adult feathers can be secondarieswere less frequent in the collections distinguished, and depending on when replace- (9% of White-wingedDoves, Z. asiatica,and 6% ment of juvenal flightfeathers typically commences of MourningDoves, Z. macroura),and no speci- (i.e., duringthe firstor secondprebasic molt), birds mens were found with retained adult secondaries. with retained flight feathers can be aged more ac- As in Columba,retained juvenal secondaries were curatelyor to a later age categorythan thosewith amongs4-s6 (e.g., Aprilspecimen White-winged uniformadult flight feathers (see Figure 1). Molt Dove CAS31444 and May specimen Mourning patterns within each near-passerine family are Dove CAS32158), and specimenswith these were summarized as follows: assignedage code SY. COLUMBIDAE I could not confirmage-specific