j. Field Ornithol., 60(3):361-368

PROBABLE DIETARY BASIS OF A COLOR VARIANT OF THE CEDAR

JOCELYNHUDON AND ALAN H. BRUSH1 Departmentof Physiologyand Neurobiology U-42, The Universityof Connecticut Storrs, Connecticut06268, USA

Abstract.--Pigmentsin the tail band of a recentlydiscovered orange form were isolatedand comparedto thoseof normal Cedar (Bombycillacedrorum). The main pigment in the yellow featherswas identifiedas a canary-xanthophyll.The orangevariants had, in addition,significant amounts (up to c. 40%) of the red carotenoidrhodoxanthin. Rectrix colordiffered widely amongvariant individuals,as a resultof differencesin the total amounts of carotenoidsand the duller melanins.Red waxy appendagesof the and the tail bandof the red-bandedJapanese Waxwing (B.japonica) contained astaxanthin and two unidentifiedred acidogeniccarotenoids. Canary-xanthophyllsand acidogeniccarotenoids are modifiedmetabolically from dietary precursors.Rhodoxanthin, by contrast,is obtaineddirectly from the diet and, presumably, depositedunmodified in the variant tail feathers. We believe that many of the orange individuals,most of whom are juveniles,ingested rhodoxanthin as nestlings.The relatively recentoccurrence of the orangecolor implies a new food sourceor a changein food choice by the adults.

VARIANTE EN COLORACION EN BOMBYCILLA CEDRORUM: PROBABLE EFECTO DE LA DIETA Resumen.--Se aislaron los pigmentosque componenel anaraniadorecientemente descu- bicrto cn la bandadel rabo dc individuosdel picotcroBombycilla cedrorum, y sccompararon con los pigmcntoscn la coloraci6nnormal dc la cspccic.E1 pigmcntoprincipal amarillo, result6scr xant6filo-canario.La variantcanaranjada comcnla adcmfis, cantidades consid- erablcs (hasta un 40%) dc rodoxantina (carotcnoidcrojo). E1 color dc las rcctriccsvari6 considcrablcmcntcentre los individuos, dcbido a difcrcncias cn la cantidad dc carotcnoidcs y mclanina.E1 rojo cerosocn el picotcronortcamcricano y la bandacn cl rabo cn cl picotcro japon6s(B. japonica)conticncn astaxantina y doscarotcnoidcs acidog6nicos quc no hah podidoscr idcntificados.Tanto cl xant6filo-canariocomo los carotcnoidcsacidog6nicos son clcmcntos de la dicta modificadosmctabolicamcntc. Pot cl contrario, la rodoxantina cs obtcnidadircctamcntc dc la dicta y probablcmcntcdcpositada sin modificarsccn las plumas dcl rabo. Los autorescrccn quc muchosde los individuosanaranjados, la mayorla dc cstos juveniles,ingiricron rodoxantina cuando cran polluclos.E1 nucvohallazgo dc anaranjado en cl rabo dc estasaves implica una novel fuentc dc alimcntoso cambiosrccicntcs cn la dicta dc los adultos.

Individual Cedar Waxwings (Bornbycillacedrorurn) in easternNorth Americamay havea tail bandthat is orangeinstead of the usualyellow. This color is not found in museumspecimens older than about 30 years and recentlyhas increaseddramatically in frequency.Furthermore, it is mostcommon in juvenilebirds (Parkesand Wood, pers.comm.). K. C. Parkes and D. S. Wood have documentedthe geographicaldistribution of the new form, and its suddenappearance in time. Seasonaland sexual dichromatisminvolving carotenoidpigments are well known in .The chemicalchanges that producesuch differences

I Addressall correspondenceto Brush.

361 362] j. Hudon and A. H. Brush J. Field Ornithol. Summer 1989 havebeen reported in a few species(Brush 1967). Color morphsare less common,but their chemicalbasis in severalspecies is well known (Brush and Seifried1968, Johnsonand Brush1972, V/31ker1964). It is possible to correlatesuch chemical differences in featherpigments with metabolic processesand, by extension,to speculateon their geneticbasis (reviewed in Brush 1981). In theseand other cases(see Buckley 1987), morphsare of long term occurrenceand appear to be stablein the population.The suddenappearance of a colorvariant in the Cedar Waxwing is therefore intriguing.Accordingly, we undertookan analysisof the pigmentsin the rectricesof orange-bandedand yellow-bandedCedar Waxwings, and the red-bandedJapanese Waxwing (B. japonica). We expectedthat char- acterizationof the pigmentdifferences between the orange-and yellow- bandedindividuals would elucidatethe causeof dimorphismin this pre- viouslymonomorphic species.

METHODS Tail feathersfrom individual Cedar Waxwings of both normal and variant colors(Table 1; collectedfrom June 1968 (CM 143398) to August 1984 (CM 162781), in Westmorelandand Alleghenycounties, Pennsyl- vania) and from a JapaneseWaxwing (ex-AMNH 665434, no data) were suppliedby the Carnegie Museum of Natural History. Additional samples,including a rectrix bearing a waxy appendagelike thosefound on secondaryremiges of adult Cedar Waxwings (UCONN 9152; West- port, Connecticut),came from the University of ConnecticutMuseum of Natural History. We weighedeach set of feather tips. Tail band colors were assessedusing color swatches(Smithe 1975), and the carotenoid pigmentsextracted in warm, acidified (HC1) pyridine (Vi51ker1936). This procedurepreserved the structureof the feather, and did not solu- bilize the duller melanin pigmentsto any major extent. It alsopermitted the extractionof carotenoidsfrom small amountsof startingmaterial, as was necessaryhere. We transferredthe carotenoidsto hexanesin a separatoryfunnel. The pigmentsin the epiphasewere washedwith distilledwater, concentrated under nitrogen,and storedover anhydroussodium sulfate in the dark. Total absorbanceand individualvisible spectra were recordedon a Perkin- Elmer model 552 spectrophotometer.We determinedthe total carotenoid contentof individual tail bandsfrom the absorbanceat 438 nm (X•,ax)in hexane, with an coefficient,Elcm, •o of 2500 (Britton 1985). Chem- icalreactions performed on wholeextracts included reduction of carbonyl groupswith sodiumborohydride in methanol(Andrewes et al. 1974), acetylationof hydroxylgroups (acetic anhydride in pyridine,Andrewes et al. 1974) and treatmentin alkaline (5% KOH) methanol(Partali et al. 1987). We separatedpigments on silicagel IB and aluminumoxide IB thin-layerchromatographic (TLC) plates(Baker-flex, J. T. Baker Chem.Co., Phillipsburg,N J) in a hexane:acetone (3:1) solventsystem. We used a Waters HPLC instrument equippedwith a Lambda Max model 481 LC variable wavelengthdetector to determinethe relative Vol.60, No. 3 DietaryBaszs of WaxwingVariant [363

TABLE1. Carotenoidcontent and compositionof tail bandsfrom normaland variant Cedar Waxwings.Band colorswere assessedusing Smithe (1975). The relativeconcentration of the dione pigmentwas calculatedfor the yellow pigmentsonly.

Carotenoid Percent Percent content rhodo- 3,3'-dione (mg/g xanthin (% of yellow Specimen Band color feather) (%) pigments)

Normal birds CM 153188 SpectrumYellow (#55) 0.26 5.8 94 CM 152531 SpectrumYellow (#55) 0.43 1.0 96 Variant birds CM 143398 Buff (#24) 0.12 22 62 CM 151128 Burnt Orange (#116) 0.37 44 82 CM 162781 Burnt Orange (#116) 0.38 24 92 CM 162773 Pratt's Rufous (#140) 0.62 36 59 concentrationof identifiedpigments in eachsample. The area under the curveof the individual pigmentsat 450 nm, a measureof concentration, was integratedby an attachedmodel 740 data module. We useda Zorbax ODS (Du Pont, Wilmington, DE) reverse phase column to separate pigments.Elution with methanol (mobile phase) was performedat 0.5 ml/min. The capacityfactor, k', a measureof mobilityon HPLC, was calculatedwith the formulak' = (tR - to)/to,where tR was the pigment retention time and to the column dead-time.

RESULTS The brightly coloredband of the rectricesin all Cedar Waxwings examined containedcarotenoid pigments. A yellow pigment occurred consistentlyin large amounts in both normal and variant birds. We identified this carotenoidas •,•-carotene-3,3'-dione(Hudon and Brush, in prep.), a probablecanary-xanthophyll (Brockmann and Vi31ker1934). This identificationwas basedon chemicalanalysis, which revealedtwo carbonyland no hydroxylgroups, and a sensitivityto alkalineconditions. Additionalsupport came from the visiblespectrum, with X,•ax= 415,438, 468 nm (Matsuno et al. 1986). The capacityfactor on HPLC (k') was 3.2. This pigmentalso predominated in the yellowbelly feathers. A minor, yellowpigment of the tail band foundin many individualscorresponded to 3'-hydroxy-e,e-caroten-3-one,another probable canary-xanthophyll (k' = 3.0) (Hudon and Brush,in prep.). Finally, an unidentifiedyellow pigment (k' = 2.45) was also detectedin someindividuals (see below). In the orange-bandedbirds, and to a lesserextent in the yellow-banded individuals,we detectedthree closely migrating red pigmentsin addition to the majoryellow pigment. This setof red pigmentsmatched completely rhodoxanthin, isolatedfrom Yew (Taxus baccata)berries, in the number of forms,their respectivemobilities on TLC and HPLC (k' of from 4.7 to 5.3), color on TLC, and relative abundance.We believethis set of red 364] J. Hudorzand A. H. Brush J.Field Ornithol. Summer 1989 pigments representsthe three cis-trarzsisomers of rhodoxanthin (3,3'- diketo-retrodehydro-/3-carotene)at the 6(6')-exocyclicdouble bond (Kay- ser and Gemmrich 1984). A different set of red pigmentswere obtained from the red tail band of the JapaneseWaxwing or the waxy appendages of Cedar Waxwings (Brush and Allen 1963). They includedastaxanthin (3,3'-dihydroxy-•,•-carotene-4,4'-dione),and two unidentified red ca- rotenoids.All boundvery tightly to the aluminum oxide TLC plates, a behaviorobserved consistently with 3-hydroxy, 4-keto-carotenoids.Their sensitivityto alkaline conditionsin methanollends further supportto this identification(acidogenic carotenoids). Rhodoxanthin does not display suchbehavior. The waxy appendageon a Cedar Waxwing rectrix con- tained the same pigmentsfound in the wing waxy appendages(asta- xanthin) plus the pigmentsfound in the tail band. In this individualthe tail band was orange and containedrhodoxanthin. We identifieddifferent colorphenotypes of the tail band and evaluated different variables in typical representativesof each (Table 1). These included the total carotenoid content, the fractional contribution of rho- doxanthin, and the fraction of yellow carotenoidsthat was •,•-carotene- 3,3'-dione.The two SpectrumYellow individualsvaried slightlyin total carotenoidcontent and containednegligible rhodoxanthin (Table 1). Rho- doxanthin varied almost 5-fold between these two individuals. The color of the tail band in the orange-bandedbirds varied in hue and saturation(or chroma). In order of increasingredness, there were bandsthat appearedBuff (#24), a poorlysaturated color, Burnt Orange (#116) of high saturation, and Pratt's Rufous (#140) of moderate saturation,according to the Munsell notations(Smithe 1975). The tail bandsof all the variantsyielded considerable rhodoxanthin, up to 40% of the total carotenoidpigments in someindividuals (Table 1). The two Burnt Orange individualsdiffered from the yellow-bandedbirds largely in respectto the depositionof increasedamounts of rhodoxanthin.Orange tail bandsvaried greatly in their total carotenoidcontent (Table 1). The rednessof the variant phenotypecorrelated broadly with pigmentcontent. The Buff tail band containedabout one-third as much pigment as the normal bands, whereas the Pratt's Rufous tail band contained almost twice as much. The Buff and Pratt's Rufous bands also contained rela- tively less •,•-carotene-3,3'-dione,while an unidentified pigment com- prised most of the remainder of the yellow pigments(Table 1). These two variants, and also to a lesserextent the Burnt Orange-tailedbirds, differed further from the yellow birds in the depositionof noticeable amounts of melanins, which produce black, grays, and browns, along with the carotenoids.In contrast,the yellow-bandedbirds had practically no residualmelanins after extractionof the carotenoidsin acidifiedpyr- idine.

DISCUSSION Ultimately, in birds, all carotenoidpigments are derivedfrom the diet (Brockmannand Vi51ker! 934, Giersbergand Stadie 1933). Nevertheless, Vol.60, No. 3 DietaryBaszs of WaxwingVariant [365 many carotenoidsare the productsof the activityof enzymeson dietary precursorcarotenoids (Brush 1981). Prominentamong the metabolites producedby birds are the canary-xanthophyllsand 4-keto-carotenoids (Brockmannand Vi31ker1934, Fox et al. 1969, V/31ker1962). Canary- xanthophyllsare modifiedfrom lutein or lutein-like precursors(Brock- mann and Vi31ker1934, Matsuno et al. 1986). The acidogenicpigments (3-hydroxy, 4-keto-carotenoids)present in the waxy tips of the Cedar Waxwing and the tail band of the JapaneseWaxwing also result from enzymaticmodification of dietaryxanthophylls (Thommen 1971, V/31ker 1943). Xanthophylls(notably lutein) are widely distributedin plants, and constitutean importantcomponent of greenleaves (Goodwin 1980). In contrast,apparently no producesrhodoxanthin enzymatically, as thereare no reportsof the endogenousproduction of rhodoxanthinin controlledfeeding experiments. Rhodoxanthinis found in someberries, notably in the plant genus Taxus(Goodwin 1980). It is alsowidespread in the leavesof gymnosperms (Czeczuga 1986), where it could be consumedby .Its known distributionin other plants is rather limited, and it is restrictedto a few angiosperms(Kayser and Gemmrich 1984, Rahman and Egger 1973) and pteridophytes(Czeczuga 1985). Presumably,the carotenoidin the variant Cedar Waxwings originatedfrom direct ingestionfrom berries or indirectlyvia insects(cp. Partali et al. 1987), and depositedunchanged in the feathersalongside the usualyellow pigment. Cedar Waxwings feed abundantlyon berriesyear-round, but alsoingest insects seasonally (Bent 1950). The young are fed on insects,but berries are added to the diet early in their lives (Bent 1950). Birdsthat normally do not encounterrhodoxanthin in their diet, when fed the pigment,deposit it in carotenoid-containingfeathers, irrespective of the feather'snatural color(Vi51ker 1955, 1957, 1958). Presumably,the processesinvolved in pigment depositiondo not discriminatebetween rhodoxanthinand the normalcarotenoid pigments (cp. with Kritzler 1943 for the use of capsanthinin feather pigmentation).Thus, no genetic changesneed be invokedto explainthe presenceof orange-bandedCedar Waxwings. Indeed, dietsthat differ in rhodoxanthinlevel could lead to the observedcolor difference,with no requirementfor an enzymeto producethe red pigmentand of geneticinformation for the expressionof the enzyme.We foundrhodoxanthin in all birdsexamined, which suggests that the pigmentis widely available.The orange-bandedbirds simply obtained more rhodoxanthin. Additional evidencefor dietary involvementcomes from the unusual patterns of orange pigmentationexhibited by somevariant individuals. For example, in one adult (USNM 566608, U.S. Natl. Mus.), the in- nermostrectrices (left r2, r3; right rl, r3, r4) were the normal yellow, but the outerrectrices (particularly left rS, r4 and right rS) were orange. In anotherbird, alsoan adult (UCONN 9152), the two innermostrectrices were yellow and the others orange. In this individual and a juvenile (UCONN 9750) somenormally yellow anterior belly feathers were tinted 366] J. Hudonand A. H. Brush J.Field Ornithol. Summer 1989 red. Presumably,these patterns reflect changesin pigment levels and availability when the feathers were formed. It would be unusual for geneticchanges to give rise to sucha variety of individual patterns.As yet, there are no recordsof the band colorin an adult Cedar Waxwing that was orangeas a first year . Data of this type are likely to be scarceas bandedjuvenile waxwingsare almostnever recaptured in their secondyear (Parkes, pers. comm.). Accordingto the diet hypothesis,deposition of rhodoxanthin in the feathersshould be contingentwith its availabilityat the time of feather growth,and couldbe derivedfrom the diet or internal storagesites. Thus, to be effectivein juvenile birds, where the orange color prevails,the pigment would have to be available at the time of early growth and productionof their rectrices.This probablyhappens in mid-Julyto August in easternNorth America. The carotenoidscould be obtaineddirectly from the diet or indirectlyfrom the eggyolk. The adultsdo not molt until later in the autumn (Dwight 1900) and presumablywould not be affected by the presenceof the pigment in the diet until that time. Possibly,the differencein frequencyof incidenceof the dimorphismbetween age classes can be attributed to the different time schedulesof feather replacement betweenthe agegroups. Such a differencewould be a functionof seasonal changesin the environmentalabundance of rhodoxanthin.A knowledge of the molt scheduleof the yellow feathertracts in birdsof differentages might be usedto reconstructthe availability of the pigment in the envi- ronment.Alternatively, if the abundanceof rhodoxanthinwere relatively constant,a prevalenceof the orange color in juvenile birds could arise from their high food intake as growing nestlings,and possibleaccumu- lation of rhodoxanthin. In individualswith a Burnt Orange tail band, the incorporationof a dietary red pigment can accountfor the color change.In other variants the explanationmust be more complex.The individualwith a Buff tail band exhibiteda highly reducedcarotenoid deposition, in particular e,e- carotene-3,3'-dione,and increasedmelanin deposition,when compared with the yellow-bandedbirds. Similar phenotypes,characterized by low carotenoidand high melanin levels,have beenproduced experimentally in Eurasian Bullfinches(Pyrrhula pyrrhula) by limiting accessto food (Schereschewsky1929). Differencesin the quantity or quality of food items might thereforehave been responsiblefor the observedcolor dif- ferences.We might expectthat nestlings,which are in a periodof rapid growth,are moresensitive to dietarydifferences than adults.The quality of the diet is a functionof the food items suppliedby the parents.Pre- sumably,in birds with yellow bandsan adequatediet was availableand the feathers resemble those in the adults. Recordsfrom museumspecimens indicate the appearanceof orange featherswas relatively recent (Parkes and Wood, pers. comm.). They have existed in the birds from the northeast United States for less than 30 yr. If a dietarychange is involved,the suddenappearance might reflect the appearanceof a new food source,a changein the abundanceof a Vol.6o, No. 3 DietaryBasis of WaxwingVariant [367 native or establishedsource, or a changein adult food choice.A studyof the current geographicaldistribution and extent within localitiesof the phenomenonmay resolvethe cause of the dimorphism in the Cedar Waxwing. The possibilityof finding variant nestlingsat the nestwould expeditethe work of correlatingthe phenotypeswith variablesof the environment,and suggestpossible solutions.

ACKNOWLEDGMENTS

We are grateful to Kenneth Parkes, Carnegie Museum of Natural History, Pittsburgh, who called our attention to the problem and provided numerous valuable information pertaining to it. K. Parkes also donatedmaterial and critically read the manuscript.We thank George A. Clark, Jr., University of ConnecticutMuseum of Natural History, for providing material, discussingthe problem and making constructivecriticisms of an earlier draft of the paper. A. P. Capparella also providedhelpful suggestions.Partial financial supportwas through the University of ConnecticutResearch Foundation. J. H. was sup- portedby a 1967 PostgraduateScholarship of the NSERC from Canada.

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