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Flight-Feather Molt Patterns and Age in North American Woodpeckers

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Flight-Feather Molt Patterns and Age in North American Woodpeckers J. Field Ornithol., 66(4):564-581 FLIGHT-FEATHER MOLT PATTERNS AND AGE IN NORTH AMERICAN WOODPECKERS PETER PYLE AND STEVE N. G. HOWELL Point ReyesBird Observatory 4990 ShorelineHighway StinsonBeach, California 94970 USA Abstract.--Specimensof 1399 North American woodpeckerswere examined to assessflight- feather replacementpatterns and their use in aging. The primaries and rectricesare fully replacedduring the first prebasicmolt in mostspecies, but fully retained in two species.In contrast,all speciestypically retain secondariesand primary covertsduring the first prebasic molt, and the regular retention of up to six secondariesduring definitiveprebasic molts is found in somebirds of mostspecies. Replacement of the primary covertsduring the second prebasic molt is incomplete, 0-5 consecutiveouter coverts typicallybeing renewed. This delayedreplacement pattern of primary coverts,not correspondingto the replacementof the primaries,may be uniquein woodpeckers(and perhapscertain kingfishers) among birds. By combiningretention patternswith differencesin color pattern and relativewear between juvenal and adult feathers,many woodpeckerscan be reliably aged through their third or fourth year of life. PATRON DE MUDA DE LAS PLUMAS DE VUELO Y EDAD EN PJ•JAROSCARPINTEROS DE NORTE•CA Sinopsis.--Seexaminaron 1399 especimenesde p•jaros carpinterosde Norte Am6rica para determinar el patr6n de reemplazode las plumasde vuelo y su utilidad para determinar la edad. Durante la primera muda preb•sicalas primariasy las rectricesson reemplazadasen su totalidad en la gran mayoriade las especiesy retenidasen dos de 6stas.En contraste, todas las especiestipicamente retienen las secundariasy las cobijasprimarias durante la primera muda preb•sicay algunosindividuos de la mayoriade las especiesretienen de forma regularhasta seis de lassecundarias. El reemplazode lascobijas primarias durante la segunda muda preb•sicaes incompleto,remplaz•ndose consecutivamente de 0-5 cobijasexteriores. Este retrasoen el reemplazode las cobijasprimarias, el cual no correspondeal reemplazo de lasprimarias, puede set 6nico en los carpinteros(y quiz•sen algunosmartin pescadores). Combinandoel patr6n de retenci6n de algunasplumas, las diferenciasen los patronesde coloraci6ny desgasteentre el plumaje de juvenil y el de los adultos,se podria determinar la edad de p•jaroscarpinteros en su tercery cuartoafio de vida. Woodpeckershave long interested North American ornithologistsre- searchingsystematics, behavioral ecology and other topicsof life history (e.g., Howell 1952;Koenig and Mumme 1987;Morrison and With 1987; Selanderand Giller 1966; Short 1965, 1971, 1982). It is thus surprising that so little attention has focusedon molt in this group. Differencesin the timing and extent of moltscan lead to accurateaging of woodpeckers, a vital component to increasinglyimportant studieson reproductive suc- cess,population ecologyand conservation-relatedmanagement. Historically,a complete annual prebasicmolt was assumedto occur in both juvenilesand adultsof mostspecies of North American woodpeckers (Bent 1939, Forbush 1927, Howell 1952, Oberholser 1974, Stone 1896). Test (1945), Stresemannand Stresemann(1966), and George (1972) were the first to point out that the secondariesare not replaced during the first prebasicmolt in certainspecies. George (1972) further indicated 564 Vol.66, •o. 4 Molt andAge in Woodpeckers [565 that the primarycoverts typically may not be replacedduring this molt, and that differencesin qualitybetween juvenile and adult feathersmay be usefulfor aging.Work in Europe (summarizedby Baker 1993, Cramp 1985, Ginn and Melville 1983) has confirmedthese findings for the first prebasicmolt in Europeanwoodpeckers, although details of primaryco- vert retention remain poorly documented. In North America, however, thisinformation has been overlookedor, at best,only vaguely recognized (CanadianWildlife Serviceand U.S. Fishand Wildlife Service1991;Jack- son 1979, 1994; Rea 1970; Roberts 1955; Short 1982; Wood 1969). Test (1945) alsomentioned the regularretention of somesecondaries during definitiveprebasic molts of adult flickers(Colaptes), an aspectof wood- pecker molt that subsequentlyhas been overlookedalmost entirely in both the Europeanand North Americanliterature. To understandfurther molt and its applicabilityto agingNorth Amer- ican woodpeckers,we examinedspecimens of all 21 extant speciesoc- curring north of Mexico for information on the timing and extent of molts,and the occurrenceand sequenceof retained flight feathers.Here we report our findings,and their usefulnessfor preciseaging. We propose that many birds can be reliablyaged up to their third or fourth year of life. METHODS Specimens'of 1399North American woodpeckers, housed at the Cali- fornia Academyof Sciences(CAS), San Francisco,Museum of Vertebrate Zoology(MVZ), Universityof California, Berkeley,and Point ReyesBird Observatory (PRBO), Stinson Beach, California, were examined (Table 1). Specimentag data, including sex, subspecies,date and location of collection,and any notationsregarding age, were noted and synthesized as part of the examination.Within each species,specimens from a wide range of geographiclocalities and/or from all recognizedsubspecies (see AmericanOrnithologists' Union 1957) were examinedfor intraspecific variation in molt patterns; no substantivedifferences due to these vari- ables,or to sex,were detected. Flight-feather molt patternsin populations of the Yellow-belliedSapsucker complex (Sphyrapicus varius, S. nuchalis, and S. ruber) were found to be very similar; therefore, these forms are lumpedin this paper.As speciesin the previouslyrecognized genus Cen- turus (American Ornithologists'Union 1957) showvery different molt patternsto those of Melanerpes,in which they are now placed,we have recognizedCenturus in this paper; this decisionwas basedon practical rather than taxonomic considerations. Terminologyof molt, plumagesand feather generationsfollows Hum- phreyand Parkes(1959; see also Thompson and Leu 1994). Generations of feathersand plumagessubsequent to fledgingare termed "juvenal," "lst basic," "2nd basic," etc., whereas "definitive" refers to feathers and plumagesthat are at least 1st basicin age (i.e., are not juvenal), but otherwiseare of unknownage. "Adult" birdsare thosein definitiveplum- age. Birds in activemolt refer to those that were showingsymmetrical 566] P. Pile and S. N. G. Howell J. Field Ornithol. Autumn 1995 Vol.66, No. 4 Moltand Age in Woodpeckers [567 replacement when collected, as indicated by missing,growing, or en- sheathed feathers. On each specimenthe flight feathers,here defined as the primaries, primary coverts,secondaries (including the tertials) and rectrices,were carefullyexamined (see Rohwer 1971). Evidenceof incompletereplace- ment and differencesin color pattern, shape and/or wear betweenju- venal and definitive feathers were recorded. Birds that were collected in activemolt were noted, and for other specimens,all retained flight feath- ers were aged and recorded by wing and position. For primary coverts, only the outer six featherswere analyzedas examinationof the inner covertscould not alwaysbe performed without risking damage to the specimens. By synthesizingall flight-featherinformation, each woodpecker was as- signedan age codefollowing the calendar-basedsystem of the Bird Band- ing Laboratory (Canadian Wildlife Service and U.S. Fish and Wildlife Service1991) as modified by Pyle et al. (1987). Codesincluded: "U/ AHY" for a bird of unknown age; "HY/SY" and "AHY/ASY" for birds in and beyond their 1st basic plumage, respectively;and "SY/TY" and "ASY/ATY"for birdsin and beyondtheir 2nd basicplumage. Here, "TY/ 4Y" and "ATY/A4Y" are used for birds in and beyond their 3rd basic plumage,and "4Y/5Y" indicateindividuals in their 4th basicplumage. In eachcase the codesrepresent birds in the 1-yrperiod betweencompletion of molts (usuallyOctober-September); the code before the slashapplies until the end of the calendaryear (31 December) and the code after the slashapplies between the beginningof the year (1 January)and the next molt.Juveniles, here defined asbirds withjuvenal body plumage that were collected before the migratory period (October), were also examined. Primaries (pl-p10) and rectrices(rl-r6) were numbered distally (out- wardor awayfrom the body) and secondaries(sl-sl 1) proximally(inward or towardthe body). Data on feather replacementand measurementsfor statisticaltests were taken from the right wing, althoughboth wingsof all specimenswere examined to assessage. Little confirmed information on flight-feathermolt patterns and aging criteria in woodpeckershas been publishedon which to base age-code determinationsof examined specimens.Indications of age on specimen labelscoincided with age-codedeterminations in virtually all cases;how- ever, it should be noted that, except for juveniles,the agesof the wood- peckerswere inferred rather than absolutelyknown. Although we present substantialevidence that our age code assignmentsare correct, confir- mation of this information through study of captive or recaptured, known-agedbirds is desirable. RESULTS AND DISCUSSION Both juvenile and adult woodpeckershave a single annual molt that usuallyoccurs in the late summerand fall. In migratoryspecies the molt can be suspendedor protracted,active replacement continuing until the followingwinter, spring or summer.Most woodpeckersfollow the same 568] P. Pyleand S. N. G. Howell J.Field Ornithol. Autumn 1995 sequenceof flight-feather replacement. Replacement of
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