Partial molt.Partial molts replace only some ofthe body con-tour feath - PDF document

Partial molt.Partial molts replace only some ofthe body con-tour feathers and rarely involve the flight feathers.Complete molt.Complete molts replace all body and flight feath-Natal down.The natal down plumage may consist ofa few scat-tered down feathers (as found on most hatchling landbirds) or itmay be a dense,fuzzy covering (as found on ducklings and gallina-ceous chicks).In birds with altricial young the natal down is gener-ally replaced a week or two after hatching before fledging by thejuvenal plumage.In loons,penguins,hawks,and waterfowl,theprecocial chicks grow a second coat ofdown before the juvenalJuvenal plumage.The juvenal plumage replaces natal down via acomplete molt called the prejuvenal molt.The juvenal plumagegenerally differs substantially from subsequent adult plumages,allowing easy separation offirst or hatch-year birds from adults.The juvenal plumage is often duller and more streaked or spottedthan that ofthe adult,will often have wing bars where the adult hasnone,and is displayed on more loosely textured contour feathers.Examine the European starling and common grackle specimensand notice how the birds in juvenal plumage are duller and greyercompared to the adults.Notice how the American robin in juvenalplumage is extensively spotted in addition to being generally dullerand browner than the adults.Replacement ofthe juvenal plumagevia the first prebasic molt often occurs within three months offledging and usually takes place on the breeding grounds (wherethe juvenile fledged).Birds in juvenal plumage are usually indistin-guishable to sex.Prebasic molt.In most north-temperate passerines,the first andadult prebasic molts usually take place from JulySeptember,justafter the breeding season.Prebasic molt usually takes place on thebreeding grounds,but may take place during fall migration or onthe winter grounds.In adults,the prebasic molt is usually completeand results in the adult basic plumage.In first or hatch-year birds,it is referred to as the first prebasic molt and results in the first pre-basic plumage.The first prebasic molt is not complete,since thefeathers ofthe primaries and tail are often not replaced.The sec-ond prebasic molt is complete,and results in the second basicplumage,which is generally the adult definitive plumage (adultMolt sequence.Molting in birds usually follows a regularsequence within and among feather tracts.In many passerines,replacement ofthe remiges begins with the tertials and the inner-most primaries (starting with the innermost primary and proceed-ing outward),followed by the secondaries (starting with the outer-most secondary and proceeding inward).Tail feathers typicallymolt centrifugally from the innermost to the outermost pair(Figure 1).Regular and symmetrical sequences offlight featherreplacement help maintain flight ability.In contrast,waterfowl(ducks,grebes,pelicans,auks) become flightless because they moltall oftheir flight feathers at the same time.Basic plumage.The basic plumage is generally worn during fall,winter,and early spring.In first or hatch-year birds,it is called thefirst basic plumage and is not the definitive (final adult) plumage,since the feathers ofthe wings and tail are generally not replaced inthe first prebasic molt.These feathers retain qualities ofthe juvenalplumage,making birds in their first basic plumage generally distin-guishable from those in their adult basic plumage.The adult basicplumage is the definitive plumage to which adults return afterevery breeding season.Juvenal passerines generally achieve theadult basic plumage by their second basic plumage.Some non-passerines (gulls,eagles) and some passerines (orioles,manakins)take more than 2 years to reach the definitive plumage.In these
      Year ofLifePlumage NameMolt Replacing PlumageExtent ofMoltFirst (hatching year)Natal downPrejuvenal moltcompleteFirst (hatching year)Juvenal plumage1prebasic moltpartialFirst (hatching year)1basic plumage1prealternate moltpartialFirst (hatching year)1alternate plumage2prebasic moltcompleteSecond Adult basic plumage (2prealternate moltpartialSecondAdult alternate plumage (2)Adult prebasic moltcomplete ThirdAdult basic plumageAdult prealternate moltpartialAfter the second year,most birds cycle through the adult basic and adult alternate plumages. Table 2.Molting schedule and plumage sequences. s1p1 Figure 1.A wing during complete molt in typical sequence,includ-ing wing feather terminology. cases,the second,third,or fourth basic plumages differ from thedefinitive plumage,and an age can be assigned these subadult birdsuntil they attain their adult basic plumage.This phenomenon iscalled delayed plumage maturation.Examine your field guide dia-grams for ring-billed and herring gulls and note the changes inplumage for 1st,2nd,and 3rd winter birds,compared to adult win-ter and breeding plumages.Prealternate molt.In some birds,the prebasic molt is the onlymolt that occurs annually;thus,breeding occurs in the basicplumage for these species (e.g.American Robin and the woodpeck-ers).In most passerines,the prealternate molt causes the replace-ment ofthe basic plumage with the alternate plumage during win-ter or spring.In hatch-year birds,it is called the first prealternatemolt and results in the first alternate plumage,whereas in adults,itis referred to as the adult prealternate molt and results in the adultprealternate plumage.Prealternate molts are generally partial,though the extent ofthe prealternate molt varies substantiallyamong species and between sexes.Alternate plumage.In adults,the alternate plumage is referredto as the adult alternate plumage,whereas in hatch-year birds,it isthe first alternate plumage.In many passerines,the adult alternateplumages ofmales differ from their adult basic plumages,whereasin females,both plumages are similar.Birds in their first alternateplumage are generally duller than those in the adult alternate  In many species ofbirds,differences in plumage coloration notonly result from age and stage in the molt cycle,but also from sexor geographic location.Many birds have strong sexual dimorphismin plumage coloration.Examine the specimens ofwarblers,bobolink,American robin,tanagers,orioles,wood duck,andkestrel exemplifying sexual dimorphism in plumage.Since in manybirds the female usually performs most or all ofthe incubation andbrooding ofthe young,she is more cryptically colored and is lessbrightly colored than the adult male (e.g.many warblers andducks).In species in which both parents sit on the nest,sexualdimorphism in plumage coloration may be little or absent (e.g.fly-catchers and wrens).Some species exhibit reverse sexual dimor-phism.In the phalaropes,the female is more brightly colored anddefends breeding territories,and the male assumes the duties ofincubation and parental care.Examine the belted kingfisher speci-mens and note how the females breast is more brightly coloredwith rufous than is the maleGeographic variation in plumage coloration may result inspecies distinguished by subspecies or species with differentofplumages.Eastern screech owls (see specimens) havetwo plumage types,red and gray phases,and their occurrencevaries systematically with location.The plumages ofmany raptors(e.g.Red-tailed Hawk and Peregrine Falcon) also varies geographi-cally,resulting in different subspecific designations regionally.     As a result ofphysical abrasion,feathers wear at the edges and theirshapes change.In birds in which thefirst prebasic molt is incomplete,theshape and amount ofwear or fadingofcertain flight feathers or primarycoverts can serve as clues for aging.The shapes ofthe rectrices,primar-ies,and primary coverts are agingcriteria for birds that retain juvenalwing and tail feathers during the firstprebasic molt.Generally,the outertwo or three rectrices,the outer pri-maries,and the outer primarycoverts are narrower and have moretapered inner webs in juvenal feath-ers,whereas the they are broader andmore truncate in adults (Figure 2).Differences in the amount ofwearbetween juvenal and adult rectrices,primaries,and primary coverts canalso provide useful clues for aging.Wear can result from abrasion tofeather tips and degradation due to solar radiation.In the early fall,shortly after the prebasic molt,retained juvenal feathers are aboutone to three months older than the corresponding adult feathersand usually show signs ofwear.Nicks in the outer webs ofthefeathers and a decrease in glossiness indicate feather wear.Adultfeathers at this time should be glossy and lack nicks.Examine thebaltimore oriole specimens.Compare the rectrices and remiges ofthe adult in basic plumage,which show little wear,with those ofthe specimen with first alternate plumage,showing extensive wearresulting from retention ofthese feathers from the juvenalplumage.Primary coverts,usually retained in the first prebasicmolt,should be faded and worn,compared to the adjacent greatersecondary coverts,which are generally replaced in the first prebasicmolt and appear glossy.Feather wear can also function in changing the plumage col-oration or pattern.The plumage worn by the male snow buntingduring summer breeding is not a separate plumage,but is actuallyjust the worn feathers ofthe basic plumage.In the late summer,prebasic molt,the snow bunting male molts into a pale brown andgray basic plumage,with feathers having pale tips.Over the fall andwinter,the pale white edges offeathers in the basic plumage wearoff,revealing a bolder black and white pattern that is fully devel-oped by the time the male has returned to his breeding grounds inspring.Such wear plumageis also evident in European starlings.Examine the starling specimens.The change from the speckledwinter plumage to the non-speckled summer plumage results notfrom molt,but from the white tips wearing offofthe contour   The anatomical features reviewed below are mostly useful for iden-tifying,aging,and sexing birds in the hand,and arent generally
Birds ofthe World AHY/ASY b Figure 2.Examples oftheshape ofvarious feathersby age (a) outer rectrices(b) outer primaries (c) theouter primary coverts. Aging,Sexing,and MoltIdentification ofbirds not only means identifying the species ofanindividual,but also can include identifying its subspecies,sex,andage.Field identification ofthe age and sex ofa bird can be impor-tant for studying many aspects ofavian ecology and evolution,including life history evolution,reproductive ecology,and behav-ioral ecology.Ornithologists use a variety ofcharacteristics to Aging, Sexing, and Molt1 Identification CharacterSpeciesSubspeciesSexAge Molt and Plumage PatternsPlumage coloration¥¥¥¥Feather wearFeather shape Other FeaturesSize (wing,tail,weight,leg,bill)¥¥¥¥ Song¥¥¥ Geographic location¥¥ Table 1.Features usefulful for identifying,aging,and sexing birds. .Bill length is the distance from the anterior end ofthe nostril to the tip ofthe bill (Figure 4c).When measuring billlength it should be noted that slight variation in bill length occursbetween seasons.Tarsus length.Tarsus length is the length between the intertarsaljoint and the last leg scale before the toes emerge (Figure 4d).Tarsus length is difficult to measure in live birds but can be helpfulin sexing fledglings ofcertain species.Weight.Weight is the mass ofan individual.Many factors caneffect weight,thus it is largely unreliable for determining age orsex.Wing formula.Wingformula refers to threeaspects ofthe primaries:the length and relativeposition ofthe primarytips,the occurrence andlength ofnotches on theprimaries,and the occur-rence ofemargination inthe outer webs ofthe pri-maries (Figure 5).Thesethree aspects ofthe wingcan be used for determin-ing the species,sex,andage ofindividuals.Feather wear can alter these features so the useofthe wing formula is unreliable except when primaries are ingood condition.The use ofthis technique is highly developed inEurope where it is used to identify a number ofspecies with verysimilar outward appearances (especially among a group ofOldWorld warblers).Skulling is a technique used to age birds and is based on the extentofpneumatization in sections ofthe skull overlying the brain (thefrontals and parietals).When a young bird fledges,the top ofitsskull consists ofa single layer ofbone:skull pneumatization is thegradual formation ofa second layer ofbone under the previousone,a process that takes four to twelve months depending on thespecies.Pneumatization produces recognizable patterns in theextent and distribution ofair pockets and small visible columns ofbone developing between the layers forming the top ofthe skull.These patterns are visible through the thin skin on the top ofabirds head.During certain times ofthe year the amount ofskullpneumatization can be used to separate hatch-year birds fromolder individuals (the skulls ofwhich are completely pneumatized)and is especially important for aging passerines,particularly in thelate summer and the fall.The skulls ofmany passerines becomecompletely pneumatized by late fall,at which time hatch-year birdsare indistinguishable from older birds.Pneumatization takes sev-eral months in some groups ofbirds,so skulling these species canbe productive into the late winter and very early spring.In order to inspect the condition ofthe skull through the skin onthe top ofthe birds head,the crown feathers are brushed aside(this is usually done by wetting the feathers).Hatch-year birds(and,in some species,second-year birds through early spring) willhave unpnuematized sections ofthe skull appearing pinkish white,contrasting with pneumatized areas which appear grayish,whitish,or pinkish white with small white dots (the columns ofbone).Theskulls ofmost after hatch-year birds will appear whitish with manyscattered small white dots (Figure 6).\f\b\b\r\n\r\b\n\b\r\bThe most reliable technique for sexing species where males andfemales share similar plumages is the presence or absence ofa cloa-cal protuberance or brood patch (for species with a long breedingseason these features can also be used to identify adults and hatch-year birds).Cloacal protuberances and brood patches are onlypresent on adults during the breeding season:during the non-breeding season other characteristics must be used.Cloacal protuberance.Cloacal protuberances are developed bybreeding male passerines to store sperm and assist in copulation(Figure 7).It results from the enlargement ofthe testes and associ-ated ducts.A typical cloacal protuberance forms a right angle to Birds ofthe World Figure 5.Examples ofnotched (a)and emarginate (b) primaries. ab Figure 6.Two common sequence patterns ofskull pneumaticization (a) periferal pattern (b) medial line pattern. a usefull as field marks.When birds can be captured for close inspec-tion,however,theses features can prove invaluable,and are widelyused iby ornithologists.Size can be a useful characteristic for the identification ofspecies,subspecies,and sex,but is not reliable for determining age exceptin a few cases (e.g.,certain blackbirds).Measurements can be par-ticularly important for sexing live passerines in the hand and studyskins in a museum collection.In most passerines males are,on average,larger than females,but because this size difference is statistical,using size alone todetermine the sex ofan individual is often unreliable.In mostNorth American passerines the sexes show a 60 80% overlap inmany size measurements (e.g.the measurement ofa large femalemay be similar to that ofa small male):in these species wing cordlength will reliably indicate sex in only 20 40% ofthe individualsmeasured (e.g.those lying in the extremes ofthe overall size distri-bution:Figure 3).Thus,for different species and individuals,vari-ous measurements ofsize may range from being nearly useless tobeing very informative.Remember that reversesexual dimor-phism (females larger than males) occurs in raptors and someother nonpasserines.Some species and subspecies whose plumages are very similar(thus difficult to identify by plumage alone) can be identified usingthe measurement ofseveral different anatomical features (e.g.fly-catchers in the genus Empidonax and sandpipers in the genusCalidris).The combination ofseveral measurements can also beused to reliably determine subspecies (e.g.,Canada Goose,SavannaSparrow).Use ofSize in the Field.Size can serve to identify some specieswhose plumages are very similar (e.g.Downy vs.HairyWoodpecker,Lesser vs.Greater Yellowlegs,Snow vs.Ross's Goose,Virginia vs.King Rail,and Sharp-shinned vs.Coopers Hawk) butthe size difference between the species in question must be moder-ately large to allow for easy identification at a distance.In somespecies size can be used for sexing individuals in the field,but islargely unreliable except in certain situations (e.g.hawks).The useofplumage characteristics and song in conjunction with size is themost reliable technique for the determination ofsex in the field.Measurements.The size ofa bird can be estimated using anynumber ofparameters,but the primary measurements used arewing cord,tail length,bill length,tarsus length,and weight.Wing Chord.Wing cord is the length ofthe wing from the wristto the tip ofthe longest primary (as measured with a ruler),and isthe most frequently used measurement (Figure 4a).Tail length.Tail length is the distance from the tip ofthe longestrectrix to the insertion ofthe two central rectrices (Figure 4b).Taillength is the second most common size measurement used but isoften difficult to estimate in live birds. \reee3354 Figure 3.Normal (bell) curves including 95% confidence intervals (a) an example ofan area ofoverlap between two similar populatan example ofits use in Spizella sparrows (c). Overlap zoneexcluding outliers Clay-coloredBrewer's Timberline Browner, moreGrayer, less Mean
2 SD abc Figure 4.Measuring the wing chord (a),the tail between the central rectrices (b),the bill from nares to tip (c) and the tarsus a b c d proximal end.Some females will have a swollen cloaca but it wills protuberance.Brood patch.The brood patch is an area ofbare skin on thebreast developed by incubating females and serves to increase thetransfer ofbody heat to the developing eggs (Figure 8).In thebrood patch Blood vessels increase in size and skin becomes thickerand fluid-filled.The brood patch lasts through the breeding seasonuntil the prebasic molt (but may recede and redevelop betweenbroods).Many North American passerine males do not formbrood patches (they do not incubate) but in a few groups wherethe male will assist the female with incubation (e.g.,vireos,mimids,Myiarchus flycatchers),an incomplete brood patch maydevelop.The production ofsong is a very reliable means for identifying andsexing birds.In most species only males sing,but in a few (e.g.Northern Cardinal and Eastern Wood Pewees) females will sing atleast occasionally (a bird that is not singing is not necessarily amale,however).Age can not be reliably determined by song,although some second-year males may give incomplete or unusualsongs.In addition to song,both sexes ofmost species produce avariety ofother vocalizations that are often distinctive,and may beespecially useful when no other techniques are available (e.g.American vs.Fish Crow,Eastern vs.Western Meadowlark,andWillow vs.Alder Flycatcher).The songs ofmany species vary withgeographic range:these dialectsare often associated withdescribed subspecies,and is the most reliable identification charac-teristic for some(e.g.Red Crossbill).Vocalizations are the primary means ofidentification used byavian researchers and in conjunction with visual identificationallow researchers to conduct systematic population censuses.\r\fGeographic area can help to identify certain species whoseplumages are nearly identical (e.g.Eastern and Western WoodPeewee,Eastern and Western Meadowlarks,Purple and RockSandpipers,and Carolina and Black-capped Chickadees:Figure 9). \t\n\r\r\b\b\t Female (full breeding) Male (full breeding) Non-breeding Figure 8.Brood patches at different stages ofdevelopment. Figure 7.The cloacal protuberance at its peak (a) and profiles ofpasserine cloacal protuberances in different breeding conditions (b). ab Females, male nonbreedingMale partial breedingMale full breeding ab Figure 9.Range ofthe Black-capped Chickadee (a) and the Carolina