J RaptorRes. 39 (4) :378-385 ¸ 2005 The Raptor ResearchFoundation, Inc. FIRST-CYCLE MOLTS IN NORTH AMERICAN FALCONIFORMES PETER PYLE1 The Institutefor Bird Populations,P O. Box 1436, Point ReyesStation, CA 94956 U.S.A. ABSTRACT.--Iexamined 1849 specimensof 20 North American Falconiform speciesto elucidate the occurrenceand nomenclatureof partial first-cyclemolts. As reported in the literature,American Kestrel (Falcosparverius) and White-tailedKite (Elanusleucurus) have relatively complete body-feather molts that occur during the first fall; in the kite, this molt can alsoinclude up to all rectricesand 2-6 secondaries, but no primaries--anunusual pattern for suchpartial moltsin first-yearbirds. Evidence of partialfirst- cyclemolts was found in 16 of 18 other species(among Pandion,Haliaeetus, Circus, Accipiteg, Asturina, Buteo,Aquila, and Falco)for whichsuch molts have not beenpreviously elucidated. Maximum extent of body-featherreplacement among individualsof these16 speciesvaried from 5-50%. On the other hand, most speciesshowed evidence that this molt could be absent(11-100% of birds remainingin juvenile plumage until commencementof the completeor near-completeprebasic molt that occursduring the first summer). I argue that thesepartial molts are best consideredpreformative molts (following Howell et al. 2003) rather than "first prebasic"molts, as defined by Humphrey and Parkes (1959). Variation in the extent and timing of preformativemolts may reflect variousconstraints according to species- specificbreeding, migrating, and foragingstrategies. The apparentlack of functionfor thismolt suggests that ancestralFalconiformes exhibited a more extensivepreformative molt, as found in related orders of birds,but that this molt has sincebecome vestigial, at leastin the larger species. KEYWO•tDS: AmericanKestrel; Falco sparverius; White-tailed Kite,, Elanus leucurus; preformative molt;, hawks; falcons. MUDAS DEL PRIMER CICLO EN FALCONIFORMES NORTEAMERICANOS R•SUMEN.--Examinfi1849 especimenesde 20 especiesnorteamericanas de Falconiformespara estable- cer la ocurrenciay la nomenclaturade mudasparciales del primer ciclo. Como habia sido informado en la literatura,Falco sparverius y Elanus leucurus presentan mudas relativamente completas de lasplumas corporalesque tienen lugar duranteel primer otofio,aunque en E. leucurusesta muda puedetambi•n incluir algunaso todaslas rectrices y 2-6 secundariaspero ningunaprimaria. Esto constituye un patr6n pocousual de mudasparciales durante el primer afio de vida. Encontrfievidencia de mudasparciales en el primer cicloen 16 de las 18 especiesadicionales (en losgrineros Pandion, Haliaeetus, Circus, Acdpit• Asturina,Buteo, Aquila y Falco)para las cualesno se habla determinadopreviamente la ocurrenciade mudasde estetipo. E1m/tximo grado de reemplazode las plumasdel cuerpoen los individuosde esas 16 especiesvari6 entre el 5% y el 50%. Por otra parte, la mayoriade las especiesmostraron evidencia de que estamuda podria estarausente, pues entre el 11% y el 100% de los individuosmantuvieron el plumajejuvenil hastacomenzar la muda prebgtsicacompleta, o casicompleta, que tiene lugar durante el primer verano.Sugiero que estasmudas preb/tsicas deben considerase mudas preformativas (siguien- do la terminologiade Howell et al. 2003) en lugar de "primerasmudas prebgtsicas", como fueron definidaspor Humphreyy Parkes(1959). La variaci6nen la extensi6nyen el momentode ocurrencia de lasmudas preformativas podria reflejar distintoslimitantes de acuerdoalas estrategiasreproductivas, de migraci6ny de forrajeo especificasde cadaespecie. La falta aparentede funcionalidadde estamuda sugiereque los Falconiformesancestrales exhibian una muda preformativamgts extensiva, como se ha documentadoen 6rdenesde avesrelacionados, pero que estamuda se ha vueltovestigial, al menosen las especiesde mayor tamm5o. [Traducci6ndel equipo editorial] North American Falconiformes exhibit various most species,juvenal plumage is reportedly re- molt strategiesduring their first year of life. In tained until the first spring or summer (when a year old), at which point a complete or near-com- plete prebasicmolt commences,usually with the • Email address:[email protected] shedding of the innermost primaries in Accipitri- 378 DECEMBER2005 FIRST-CYCLEMOLTS IN FALCONIFORMES 379 dae or the medial primaries in Falconidae (e.g., ing their first year (age = 0-12 mo), prior to ini- Miller 1941, Palmer 1988, Forsman 1999, Wheeler tiation of primary molt, and 622 specimens 2003). In Aanerican Kestrel (Falcosparverius) and collected in their secondyear (12-24 mo old) or certain kites, by contrast,most to all juvenal body later. feathers are replaced during the first fall, well be- METHODS fore molt of the primaries commencesduring the followingsummer (Bent 1937, 1938, Parkes1955, Specimensof Falconiformeswere examined at the Cal- Palmer 1988, Miller and Smallwood 1997). ifornia Academy of Sciences(CAS), San Francisco,the Museum of Vertebrate Zoology (MVZ), Berkeley,and the For some species of Falconiformes, a limited National Museum of Natural History (USNM), Washing- number of body feathers are reported to be re- ton, DC. Specimens were collected throughout North, placed during the first fall, winter, or spring,prior Central, and South America, but all specimens repre- to the sheddingof primariesduring the first spring sented speciesor subspeciesexhibiting boreal breeding or summer.For example, Wheeler (2003) reported cycles.Data are presented for 20 specieswith N > 16 first-yearindividuals examined (Table 1). that in the Red-shouldered Hawk (see Table I for Specimensexamined included birds collected during scientific names), "the first prebasic molt begins their first year of life, prior to the shedding of primaries on the breast, then is noticeable on the back and during the first complete molt, and birds determined to scapulars"before molt of primaries begins, and be in their secondyear of life. Age of first-yearbirds was Forsman (1999) reported that in the Northern determined by plumage features (Palmer 1988, Wheeler 2003), the presenceof indicativefault bars (Hammers- Harrier, "singlebody-feathers and tail-feathersmay trom 1967), tapered and relativelyworn outer primaries be replaced from late winter" prior to the com- and rectrices, and absence of wear and color patterns plete molt the following May to October. Similar among flight feathersindicating previous molts. Birds in limited molts in fall, winter, or spring have been their secondyear were aged by the presenceof predefi- reported for Osprey(Bent 1937), Northern Gos- nitive plumage in some speciesor the retention of juve- nal feathersduring the first "complete" molt, particular- hawk (Bent 1937, Dement'ev and Gladkov 1951, ly among the lessercoverts, on the rump, or within the Forsman 1999), Gray Hawk (Dickey and van Ros- secondaries (Wheeler 2003). sem 1938, Wheeler 2003), and several speciesof Each first-yearspecimen was examined carefullyfor re- Falconidae (Cramp and Simmons 1980, Forsman placed body feathers in patterns indicating molt. Body 1999, Wheeler 2003). molt in Falconiformestypically begins on the head and throat and proceeds caudally (Palmer 1988, Wheeler Most authors consider this limited body-feather 2003). Thus, feathers showingwear patterns suggesting replacement to be the initiation of the prebasic replacement in a caudal direction were assumedto have molt at a year of age (hereafter, "first complete resulted from molt rather than adventitiousreplacement molt") rather than a separatemolt; indeed, Wheel- (e.g., after accidentalloss). Replaced feathers were often er (2003) even interpretsthe fall moltsin first-year intermediate in color or patterning between those of first-yearand second-yearbirds (Fig. 1), facilitatingtheir AanericanKestrel and kites as part of the first com- identification. The proportion of newly-replacedbody plete molt, terminating with the flight feathersthe feathers,to the nearest5%, wasestimated for each spec- following summer. This interpretation appears to imen. Those showing<2.5% replacementwere scoredas disregard the additional body molt that occursin 0%, further ensuring that birds with adventitiouslyre- one-year-oldbirds concurrent with flight-feather placed featherswere not included in the sample evincing molt. All primaries, secondaries,and rectriceswere also molt in these species(Parkes 1955, Palmer 1988). examined for evidence of symmetrical replacement in- Herremans and Louette (2000), on the other dicating molt. Secondarieswere numbered proximally hand, document that such molts in certain Old- from the outermost (sl) to the innermost (s13 in most World speciesof Accipiterare distinct from the first species) feather. complete molt. Second-yearbirds were examined for uniformity of feather generations,particularly in tractsfor which par- Thus, there remains confusion about both the tial molts were detected in first-yearbirds. The goal of occurrence of partial first-cyclemolts in Falconi- this examination was to assess whether or not feathers formes and whether or not body-feather replace- replaced during the first year, prior to initiation of pri- ment in the first fall, winter, or spring should be mary molt, had been replaced for a secondtime during consideredpart of a separatepartial molt or asthe the first complete molt. initiation of the first complete molt. To investigate RESULTS the occurrence and extent of partial first-cycle molts in Falconiformes,I examined 1227 speci- Partial First-year Molts in White-tailed Kite and mens of 20 North