Hidden dichromatism in the Burrowing Parrot (Cyanoliseus patagonus) as revealed by spectrometric colour analysis

Juan F. Masello; Thomas Lubjuhn; Petra Quillfeldt

doi:10.56178/eh.v24i1.729

Articles Published 01 August 2009 https://doi.org/10.56178/eh.v24i1.729

Hidden dichromatism in the Burrowing Parrot (Cyanoliseus patagonus) as revealed by spectrometric colour analysis

Burrowing Parrot Patagonia psittacofulvin-based coloration psittacofulvins sex differences sexual dichromatism structural coloration

Juan F. Masello Max Planck Institute for Ornithology, Vogelwarte Radolfzell. Schlossallee 2, D-78315 Radolfzell, Germany

Thomas Lubjuhn Institut für Evolutionsbiologie und Ökologie, Rheinische Friedrich-Wilhelms-Universität Bonn. Bonn, Germany

Petra Quillfeldt Max Planck Institute for Ornithology, Vogelwarte Radolfzell. Schlossallee 2, D-78315 Radolfzell, Germany

Abstract

Bird colour perception differs fundamentally from that of humans. Birds have more cone types in the retina, including UV or violet cones, which enable them to perceive a wider spectral range. Thus, human colour perception can be deceiving when assessing functional aspects of bird plumage coloration, such as the intensity of sexual selection. In this study we measured reflectance spectra of different plumage regions of male and female Burrowing Parrot (Cyanoliseus patagonus) individuals. Although not obvious to human eyes, spectrometry revealed that adults are sexually dichromatic. Plumage regions with structure-based (blue) and structure-psittacofulvin pigment-based (green) coloration differed in achromatic brightness. In contrast, the psittacofulvin-based (red) region differed in spectral shape between the sexes. Thus, Burrowing Parrot is among the growing number of bird species which were formerly classed as sexually monochromatic based on human vision, but which are actually sexually dichromatic.

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References

ANDERSSON M (1994) Sexual selection. Princeton Uni-versity Press, Princeton
ANDERSSON S, ÖRNBORG J AND ANDERSSON M (1998)Ultraviolet sexual dimorphism and assortativemating in blue tits. Proceedings of the Royal Society ofLondon B 265:445–450
BADYAEV AV AND HILL GE (2003) Avian sexual dichroma-tism in relation to phylogeny and ecology. AnnualReview of Ecology, Evolution and Systematics 34:27–49
BENNETT ATD, CUTHILL IC, PARTRIDGE JC AND LUNAU K(1997) Ultraviolet plumage colours predict matepreferences in starlings. Proceedings of the NationalAcademy of Sciences 94:8618–8621
BLANK SM, KUTZSCHER C, MASELLO JF, PILGRIM RLC ANDQUILLFELDT P (2007) Stick-tight fleas in the nostrilsand below the tongue: evolution of an extraordi-nary infestation site in Hectopsylla (Siphonaptera:Pulicidae). Zoological Journal of the Linnean Society149:117–137
BURKHARDT D (1989) UV vision: a bird’s eye view offeathers. Journal of Comparative Physiology A164:787–796
CABRERA AL (1971) Fitogeografía de la RepúblicaArgentina. Boletín de la Sociedad Argentina de Botánica14:1–42
CUTHILL IC, BENNETT ATD, PARTRIDGE JC AND MAIER EJ(1999) Plumage reflectance and the objectiveassessment of avian sexual dichromatism. Ameri-can Naturalist 153:183–200
DOUCET SM AND MONTGOMERIE R (2003) Multiple sexualornaments in satin bowerbirds: ultraviolet plum-age and bowers signal different aspects of malequality. Behavioral Ecology 14:503–509
DYCK J (1971a) Structure and spectral reflectance ofgreen and blue feathers of the rose-faced lovebird(Agapornis roseicollis). Biologiske Sckrifter 18:1–67
DYCK J (1971b) Structure and colour-production ofthe blue barbs of Agapornis roseicollis and Cotingamaynana. Zeitschrift für Zellforschung 115:17–29
DYCK J (1977) Feather ultrastructure of Pesquet’sParrot Psittrichas fulgidus. Ibis 119:364–366
DYCK J (1992) Reflectance of plumage areas coloredby green feather pigments. Auk 109:293–301
EATON MD (2005) Human vision fails to distinguishwidespread sexual dichromatism among sexually“monochromatic” birds. Proceedings of the NationalAcademy of Sciences 102:10942–10946
ENDLER JA (1990) On the measurement and classifica-tion of colour in studies of animal colour patterns.Biological Journal of the Linnean Society 41:315–352
ENDLER JA AND THÉRY M (1996) Interacting effects oflek placement, display behavior, ambient light, andcolor patterns in three Neotropical forest-dwellingbirds. American Naturalist 148:421–452
FINGER E, BURKHARDT D AND DYCK J (1992) Avian plum-age colors. Origin of UV reflection in a black parrot.Naturwissenschaften 79:187–188
HEINSOHN R, LEGGE S AND ENDLER JA (2005) Extremereversed sexual dichromatism in a bird without sexrole reversal. Science 309:617–619
HILL GE AND MCGRAW KJ (2006) Bird coloration. Har-vard University Press, Cambridge and London
JACOBS GH (1981) Comparative color vision. AcademicPress, New York
JONES IL AND HUNTER FM (1999) Experimental evi-dence for mutual inter- and intrasexual selectionfavouring a crested auklet ornament. AnimalBehaviour 57:521–528
KRUKENBERG CFW (1882) Die federfarbstoffe der psit-taciden. Vergleichend-physiologische Studien 2:29–36
LANGMORE NE AND BENNETT ATD (1999) Strategic con-cealment of sexual identity in an estrildid finch. Pro-ceedings of the Royal Society of London B 266:543–550
LUBJUHN T AND SAUER KP (1999) DNA fingerprintingand profiling in behavioural ecology. Pp. 39–52 in:EPPLEN JT AND LUBJUHN T (eds) DNA profiling andDNA fingerprinting. Birkhäuser Verlag, Basel
LUBJUHN T, SRAMKOVA A, MASELLO JF, QUILLFELDT P ANDEPPLEN JT (2002) Truly hypervariable DNA finger-prints due to exceptionally high mutation rates.Electrophoresis 23:517–519
MAHLER BA AND KEMPENAERS B (2002) Objectiveassessment of sexual plumage dichromatism in thePicui Dove. Condor 104:248–254
MASELLO JF, CHOCONI RG, HELMER M, KREMBERG T, LUB-JUHN T AND QUILLFELDT P (2009) Do leucocytes reflectcondition in nestling burrowing parrots (Cyanoliseuspatagonus) in the wild? Comparative Biochemistry andPhysiology A 152:176–181
MASELLO JF, CHOCONI RG, SEHGAL RMN, TELL LA ANDQUILLFELDT P (2006a) Blood and intestinal parasitesin wild Psittaciformes: a case study of BurrowingParrots (Cyanoliseus patagonus). Ornitología Neotro-pical 17:515–529
MASELLO JF, LUBJUHN T AND QUILLFELDT P (2008) Is thestructural and psittacofulvin-based colouration ofwild Burrowing Parrots Cyanoliseus patagonuscondition dependent? Journal of Avian Biology39:653–662
MASELLO JF, PAGNOSSIN GA, PALLEIRO GE AND QUILL-FELDT P (2001) Use of miniature security cameras torecord behaviour of burrow-nesting birds. Vogel-warte 41:150–154
MASELLO JF, PAGNOSSIN ML, LUBJUHN T AND QUILLFELDTP (2004) Ornamental non-carotenoid red feathersof wild Burrowing Parrots. Ecological Research19:421–432
MASELLO JF, PAGNOSSIN ML, SOMMER C AND QUILLFELDTP (2006b) Population size, provisioning frequency,flock size and foraging range at the largest knowncolony of Psittaciformes: the Burrowing Parrots ofthe north-eastern Patagonian coastal cliffs. Emu106:69–79
MASELLO JF AND QUILLFELDT P (2002) Chick growthand breeding success of the Burrowing Parrot.Condor 104:574–586
MASELLO JF AND QUILLFELDT P (2003) Body size, bodycondition and ornamental feathers of BurrowingParrots: Variation between andears and sexes,assortative mating and influences on breeding suc-cess. Emu 103:149–161
MASELLO JF AND QUILLFELDT P (2004a) Consequencesof La Niña phase of ENSO for the survival andgrowth of nestling Burrowing Parrots on the Atlan-tic coast of South America. Emu 104:337–346
MASELLO JF AND QUILLFELDT P (2004b) Are haemato-logical parameters related to body condition, orna-mentation and breeding success in wild burrowingparrots Cyanoliseus patagonus? Journal of Avian Biology35:445–454
MASELLO JF AND QUILLFELDT P (2008) Klimawandel undbrutverhalten: erfolgreich brüten in wechselhafterumwelt? Eine fallstudie am felsensittich. Vogelwarte46:302–303
MASELLO JF, SRAMKOVA A, QUILLFELDT P, EPPLEN JT ANDLUBJUHN T (2002) Genetic monogamy in burrow-ing parrots Cyanoliseus patagonus? Journal of AvianBiology 33:99–103
MAY S HL, MCGRAW KJ, RITCHISON G, COOPER S, RUSHV AND PARKER RS (2004) Sexual dichromatism in theandellow-breasted chat Icteria virens: spectropho-tometric analysis and biochemical basis. Journal ofAvian Biology 35:125–134
MCGRAW KJ AND NOGARE MC (2004) Carotenoid pig-ments and the selectivity of psittacofulvin-basedcoloration systems in parrots. Comparative Biochem-istry and Physiology B 138:229–233
MCGRAW KJ AND NOGARE MC (2005) Distribution ofunique red feather pigments in parrots. BiologyLetters 1:38–43
MEY E, MASELLO JF AND QUILLFELDT P (2002) Chewinglice (Insecta, Phthiraptera) of the Burrowing ParrotCyanoliseus p. patagonus (Vieillot) from Argentina.Rudolstädter Naturhistorische Schriften, Supplement4:99–112
MØLLER AP AND BIRKHEAD TR (1994) The evolution ofplumage brightness in birds is related to extra-pairpaternity. Evolution 48:1089–1100
MORELLI R, LOSCALZO R, STRADI R, BERTELLI A AND FALCHIM (2003) Evaluation of the antioxidant activity ofnew carotenoid-like compounds by electron para-magnetic resonance. Drugs under Experimental andClinical Research 29:95–100
MORENO J, MERINO S, LOBATO E, RODRÍGUEZ-GIRONÉSMA AND VÁSQUEZ RA (2007) Sexual dimorphism andparental roles in the thorn-tailed rayadito (Furnari-idae). Condor 109:312–320
OWENS IPF AND HARTLEY IR (1998) Sexual dimorphismin birds: why are there so many different forms ofdimorphism? Proceedings of the Royal Society of LondonB 265:397–407
PEARN SM, BENNETT ATD AND CUTHILL IC (2001) Ultra-violet vision, fluorescence and mate choice in aparrot, the budgerigar Melopsittacus undulatus. Pro-ceedings of the Royal Society of London B 268:2273–2279
PEARN SM, BENNETT ATD AND CUTHILL IC (2003) Therole of ultraviolet A-reflectance and ultravioletA-induced fluorescence in the appearance of bud-gerigar plumage: insights from spectrofluorome-try and reflectance spectrophotometry. Proceedingsof the Royal Society of London B 270:859–865
PRUM RO AND TORRES R (2003) Structural colourationof avian skin: convergent evolution of coherentlyscattering dermal collagen arrays. Journal of Exper-imental Biology 206:2409–2429
PRUM RO, TORRES R, WILLIAMSON S AND DYCK J (1999)Two-dimensional Fourier analysis of the spongymedullary keratin of structurally coloured featherbarbs. Proceedings of the Royal Society of London B266:13–22
QUESADA J AND SENAR JC (2006) Comparing plumagecolour measurements obtained directly from livebirds and from collected feathers: the case of thegreat tit Parus major. Journal of Avian Biology37:609–616
SANTOS SICO, ELWARD B AND LUMEIJ JT (2006) Sexualdichromatism in the Blue-fronted Amazon Parrot(Amazona aestiva) revealed by multiple-angle spec-trometry. Journal of Avian Medicine and Surgery20:8–14
SHAWKEY MD, ESTES AM, SIEFFERMAN LM AND HILL GE(2003) Nanostructure predicts intraespecific varia-tion in ultraviolet-blue plumage colour. Proceedingsof the Royal Society of London B 270:1455–1460
SHAWKEY MD AND HILL GE (2005) Carotenoids needstructural colours to shine. Biology Letters 1:121–124
SHAWKEY MD AND HILL GE (2006) Significance of abasal melanin layer to production of non-irides-cent structural plumage color: evidence from anamelanotic Steller’s jay (Cyanocitta stelleri). Journalof Experimental Biology 209:1245–1250
SOKAL RR AND ROHLF FJ (1994) Biometry. The principlesand practice of statistics in biological research. Thirdedition. Freeman and Company, New York
STRADI R, PINI E AND CELENTANO G (2001) The chemicalstructure of the pigments in Ara macao plumage.Comparative Biochemistry and Physiology B 130:57–63
TUBARO PL, LIJTMAER DA AND LOUGHEED SC (2005)Cryptic dichromatism and seasonal color variationin the diademed tanager. Condor 107:648–656
VERONELLI M, ZERBI G AND STRADI R (1995) In situresonance raman spectra of carotenoids in birds’feathers. Journal of Raman Spectroscopy 26:683–692
VÖLKER O (1936) Über den gelben federfarbstoff desWellensittichs (Melopsittacus undulatus (Shaw)).Journal für Ornithologie 84:618–630
VÖLKER O (1937) Über fluoreszierende, gelbe feder-pigment bei papageien, eine neue klasse von feder-farbstoffen. Journal für Ornithologie 85:136–146
VÖLKER O (1942) Die gelben und roten federfarbstoffeder papageien. Biologisches Zentralblatt 62:8–13

How to cite

Juan F. Masello, Thomas Lubjuhn , Petra Quillfeldt (2009). Hidden dichromatism in the Burrowing Parrot (Cyanoliseus patagonus) as revealed by spectrometric colour analysis. El Hornero, Vol. 24 No. 1 (2009), 47-55. https://doi.org/10.56178/eh.v24i1.729

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[1] ANDERSSON M (1994) Sexual selection. Princeton Uni-versity Press, Princeton

[2] ANDERSSON S, ÖRNBORG J AND ANDERSSON M (1998)Ultraviolet sexual dimorphism and assortativemating in blue tits. Proceedings of the Royal Society ofLondon B 265:445–450

[3] BADYAEV AV AND HILL GE (2003) Avian sexual dichroma-tism in relation to phylogeny and ecology. AnnualReview of Ecology, Evolution and Systematics 34:27–49

[4] BENNETT ATD, CUTHILL IC, PARTRIDGE JC AND LUNAU K(1997) Ultraviolet plumage colours predict matepreferences in starlings. Proceedings of the NationalAcademy of Sciences 94:8618–8621

[5] BLANK SM, KUTZSCHER C, MASELLO JF, PILGRIM RLC ANDQUILLFELDT P (2007) Stick-tight fleas in the nostrilsand below the tongue: evolution of an extraordi-nary infestation site in Hectopsylla (Siphonaptera:Pulicidae). Zoological Journal of the Linnean Society149:117–137

[6] BURKHARDT D (1989) UV vision: a bird’s eye view offeathers. Journal of Comparative Physiology A164:787–796

[7] CABRERA AL (1971) Fitogeografía de la RepúblicaArgentina. Boletín de la Sociedad Argentina de Botánica14:1–42

[8] CUTHILL IC, BENNETT ATD, PARTRIDGE JC AND MAIER EJ(1999) Plumage reflectance and the objectiveassessment of avian sexual dichromatism. Ameri-can Naturalist 153:183–200

[9] DOUCET SM AND MONTGOMERIE R (2003) Multiple sexualornaments in satin bowerbirds: ultraviolet plum-age and bowers signal different aspects of malequality. Behavioral Ecology 14:503–509

[10] DYCK J (1971a) Structure and spectral reflectance ofgreen and blue feathers of the rose-faced lovebird(Agapornis roseicollis). Biologiske Sckrifter 18:1–67

[11] DYCK J (1971b) Structure and colour-production ofthe blue barbs of Agapornis roseicollis and Cotingamaynana. Zeitschrift für Zellforschung 115:17–29

[12] DYCK J (1977) Feather ultrastructure of Pesquet’sParrot Psittrichas fulgidus. Ibis 119:364–366

[13] DYCK J (1992) Reflectance of plumage areas coloredby green feather pigments. Auk 109:293–301

[14] EATON MD (2005) Human vision fails to distinguishwidespread sexual dichromatism among sexually“monochromatic” birds. Proceedings of the NationalAcademy of Sciences 102:10942–10946

[15] ENDLER JA (1990) On the measurement and classifica-tion of colour in studies of animal colour patterns.Biological Journal of the Linnean Society 41:315–352

[16] ENDLER JA AND THÉRY M (1996) Interacting effects oflek placement, display behavior, ambient light, andcolor patterns in three Neotropical forest-dwellingbirds. American Naturalist 148:421–452

[17] FINGER E, BURKHARDT D AND DYCK J (1992) Avian plum-age colors. Origin of UV reflection in a black parrot.Naturwissenschaften 79:187–188

[18] HEINSOHN R, LEGGE S AND ENDLER JA (2005) Extremereversed sexual dichromatism in a bird without sexrole reversal. Science 309:617–619

[19] HILL GE AND MCGRAW KJ (2006) Bird coloration. Har-vard University Press, Cambridge and London

[20] JACOBS GH (1981) Comparative color vision. AcademicPress, New York

[21] JONES IL AND HUNTER FM (1999) Experimental evi-dence for mutual inter- and intrasexual selectionfavouring a crested auklet ornament. AnimalBehaviour 57:521–528

[22] KRUKENBERG CFW (1882) Die federfarbstoffe der psit-taciden. Vergleichend-physiologische Studien 2:29–36

[23] LANGMORE NE AND BENNETT ATD (1999) Strategic con-cealment of sexual identity in an estrildid finch. Pro-ceedings of the Royal Society of London B 266:543–550

[24] LUBJUHN T AND SAUER KP (1999) DNA fingerprintingand profiling in behavioural ecology. Pp. 39–52 in:EPPLEN JT AND LUBJUHN T (eds) DNA profiling andDNA fingerprinting. Birkhäuser Verlag, Basel

[25] LUBJUHN T, SRAMKOVA A, MASELLO JF, QUILLFELDT P ANDEPPLEN JT (2002) Truly hypervariable DNA finger-prints due to exceptionally high mutation rates.Electrophoresis 23:517–519

[26] MAHLER BA AND KEMPENAERS B (2002) Objectiveassessment of sexual plumage dichromatism in thePicui Dove. Condor 104:248–254

[27] MASELLO JF, CHOCONI RG, HELMER M, KREMBERG T, LUB-JUHN T AND QUILLFELDT P (2009) Do leucocytes reflectcondition in nestling burrowing parrots (Cyanoliseuspatagonus) in the wild? Comparative Biochemistry andPhysiology A 152:176–181

[28] MASELLO JF, CHOCONI RG, SEHGAL RMN, TELL LA ANDQUILLFELDT P (2006a) Blood and intestinal parasitesin wild Psittaciformes: a case study of BurrowingParrots (Cyanoliseus patagonus). Ornitología Neotro-pical 17:515–529

[29] MASELLO JF, LUBJUHN T AND QUILLFELDT P (2008) Is thestructural and psittacofulvin-based colouration ofwild Burrowing Parrots Cyanoliseus patagonuscondition dependent? Journal of Avian Biology39:653–662

[30] MASELLO JF, PAGNOSSIN GA, PALLEIRO GE AND QUILL-FELDT P (2001) Use of miniature security cameras torecord behaviour of burrow-nesting birds. Vogel-warte 41:150–154

[31] MASELLO JF, PAGNOSSIN ML, LUBJUHN T AND QUILLFELDTP (2004) Ornamental non-carotenoid red feathersof wild Burrowing Parrots. Ecological Research19:421–432

[32] MASELLO JF, PAGNOSSIN ML, SOMMER C AND QUILLFELDTP (2006b) Population size, provisioning frequency,flock size and foraging range at the largest knowncolony of Psittaciformes: the Burrowing Parrots ofthe north-eastern Patagonian coastal cliffs. Emu106:69–79

[33] MASELLO JF AND QUILLFELDT P (2002) Chick growthand breeding success of the Burrowing Parrot.Condor 104:574–586

[34] MASELLO JF AND QUILLFELDT P (2003) Body size, bodycondition and ornamental feathers of BurrowingParrots: Variation between andears and sexes,assortative mating and influences on breeding suc-cess. Emu 103:149–161

[35] MASELLO JF AND QUILLFELDT P (2004a) Consequencesof La Niña phase of ENSO for the survival andgrowth of nestling Burrowing Parrots on the Atlan-tic coast of South America. Emu 104:337–346

[36] MASELLO JF AND QUILLFELDT P (2004b) Are haemato-logical parameters related to body condition, orna-mentation and breeding success in wild burrowingparrots Cyanoliseus patagonus? Journal of Avian Biology35:445–454

[37] MASELLO JF AND QUILLFELDT P (2008) Klimawandel undbrutverhalten: erfolgreich brüten in wechselhafterumwelt? Eine fallstudie am felsensittich. Vogelwarte46:302–303

[38] MASELLO JF, SRAMKOVA A, QUILLFELDT P, EPPLEN JT ANDLUBJUHN T (2002) Genetic monogamy in burrow-ing parrots Cyanoliseus patagonus? Journal of AvianBiology 33:99–103

[39] MAY S HL, MCGRAW KJ, RITCHISON G, COOPER S, RUSHV AND PARKER RS (2004) Sexual dichromatism in theandellow-breasted chat Icteria virens: spectropho-tometric analysis and biochemical basis. Journal ofAvian Biology 35:125–134

[40] MCGRAW KJ AND NOGARE MC (2004) Carotenoid pig-ments and the selectivity of psittacofulvin-basedcoloration systems in parrots. Comparative Biochem-istry and Physiology B 138:229–233

[41] MCGRAW KJ AND NOGARE MC (2005) Distribution ofunique red feather pigments in parrots. BiologyLetters 1:38–43

[42] MEY E, MASELLO JF AND QUILLFELDT P (2002) Chewinglice (Insecta, Phthiraptera) of the Burrowing ParrotCyanoliseus p. patagonus (Vieillot) from Argentina.Rudolstädter Naturhistorische Schriften, Supplement4:99–112

[43] MØLLER AP AND BIRKHEAD TR (1994) The evolution ofplumage brightness in birds is related to extra-pairpaternity. Evolution 48:1089–1100

[44] MORELLI R, LOSCALZO R, STRADI R, BERTELLI A AND FALCHIM (2003) Evaluation of the antioxidant activity ofnew carotenoid-like compounds by electron para-magnetic resonance. Drugs under Experimental andClinical Research 29:95–100

[45] MORENO J, MERINO S, LOBATO E, RODRÍGUEZ-GIRONÉSMA AND VÁSQUEZ RA (2007) Sexual dimorphism andparental roles in the thorn-tailed rayadito (Furnari-idae). Condor 109:312–320

[46] OWENS IPF AND HARTLEY IR (1998) Sexual dimorphismin birds: why are there so many different forms ofdimorphism? Proceedings of the Royal Society of LondonB 265:397–407

[47] PEARN SM, BENNETT ATD AND CUTHILL IC (2001) Ultra-violet vision, fluorescence and mate choice in aparrot, the budgerigar Melopsittacus undulatus. Pro-ceedings of the Royal Society of London B 268:2273–2279

[48] PEARN SM, BENNETT ATD AND CUTHILL IC (2003) Therole of ultraviolet A-reflectance and ultravioletA-induced fluorescence in the appearance of bud-gerigar plumage: insights from spectrofluorome-try and reflectance spectrophotometry. Proceedingsof the Royal Society of London B 270:859–865

[49] PRUM RO AND TORRES R (2003) Structural colourationof avian skin: convergent evolution of coherentlyscattering dermal collagen arrays. Journal of Exper-imental Biology 206:2409–2429

[50] PRUM RO, TORRES R, WILLIAMSON S AND DYCK J (1999)Two-dimensional Fourier analysis of the spongymedullary keratin of structurally coloured featherbarbs. Proceedings of the Royal Society of London B266:13–22

[51] QUESADA J AND SENAR JC (2006) Comparing plumagecolour measurements obtained directly from livebirds and from collected feathers: the case of thegreat tit Parus major. Journal of Avian Biology37:609–616

[52] SANTOS SICO, ELWARD B AND LUMEIJ JT (2006) Sexualdichromatism in the Blue-fronted Amazon Parrot(Amazona aestiva) revealed by multiple-angle spec-trometry. Journal of Avian Medicine and Surgery20:8–14

[53] SHAWKEY MD, ESTES AM, SIEFFERMAN LM AND HILL GE(2003) Nanostructure predicts intraespecific varia-tion in ultraviolet-blue plumage colour. Proceedingsof the Royal Society of London B 270:1455–1460

[54] SHAWKEY MD AND HILL GE (2005) Carotenoids needstructural colours to shine. Biology Letters 1:121–124

[55] SHAWKEY MD AND HILL GE (2006) Significance of abasal melanin layer to production of non-irides-cent structural plumage color: evidence from anamelanotic Steller’s jay (Cyanocitta stelleri). Journalof Experimental Biology 209:1245–1250

[56] SOKAL RR AND ROHLF FJ (1994) Biometry. The principlesand practice of statistics in biological research. Thirdedition. Freeman and Company, New York

[57] STRADI R, PINI E AND CELENTANO G (2001) The chemicalstructure of the pigments in Ara macao plumage.Comparative Biochemistry and Physiology B 130:57–63

[58] TUBARO PL, LIJTMAER DA AND LOUGHEED SC (2005)Cryptic dichromatism and seasonal color variationin the diademed tanager. Condor 107:648–656

[59] VERONELLI M, ZERBI G AND STRADI R (1995) In situresonance raman spectra of carotenoids in birds’feathers. Journal of Raman Spectroscopy 26:683–692

[60] VÖLKER O (1936) Über den gelben federfarbstoff desWellensittichs (Melopsittacus undulatus (Shaw)).Journal für Ornithologie 84:618–630

[61] VÖLKER O (1937) Über fluoreszierende, gelbe feder-pigment bei papageien, eine neue klasse von feder-farbstoffen. Journal für Ornithologie 85:136–146

[62] VÖLKER O (1942) Die gelben und roten federfarbstoffeder papageien. Biologisches Zentralblatt 62:8–13