Journal of Ornithology

, Volume 159, Issue 2, pp 545–554 | Cite as

Patterns of variation in eggshell colour of Mountain Bluebirds (Sialia currucoides) provide mixed support for the sexually selected eggshell colour hypothesis

  • Jeannine A. Randall
  • Russell D. Dawson
Original Article


Determining the functional significance of ornamental traits and whether they are shaped by sexual selection requires understanding how they vary among individuals, and their relationship with other measures of quality. Conspicuous eggshell coloration is a trait that may have evolved through sexual selection as a signal of female quality. This hypothesis is based on the possibility that the pigment used to colour blue-green eggs is limited and potentially costly to allocate to eggshells. We investigated the signalling potential of blue-green eggshell colour by quantifying patterns of within- and among-clutch colour variation in Mountain Bluebirds (Sialia currucoides) to determine if pigment was limited and if egg colour traits are intrinsic to individual females. We also explored relationships over two breeding seasons between eggshell colour and other female traits and investment in eggs. Eggshell colour was highly repeatable within clutches for most measures, and relatively consistent between breeding events in different years, indicating that eggshell colour is an intrinsic trait. Eggs in second clutches within a season had less saturated blue-green colour than in first clutches, and within clutches, later-laid eggs were brighter but generally less blue-green in colour than earlier laid eggs, providing evidence of pigment limitation. However, associations between eggshell colour and other female traits and investment in eggs were less clear, and inconsistent among study years. Our findings suggest that there is potential for blue-green egg colour to function as a signal of female quality, but further study is needed to determine if blue-green eggshell colour is a truly informative signal.


Eggshell colour Female traits Quality signalling Blue-green 


Unterschiedliche Farbmuster der Eier des Berghüttensängers ( Sialia currucoides ) bieten eine unklare Unterstützung der auf geschlechtlicher Selektion beruhenden “Eischalenfarben-Hypothese”

Um die funktionelle Bedeutung schmückender, dekorativer Merkmale zu ermitteln und auch, ob sie ein Ergebnis sexueller Selektion sind, muss man verstehen, wie sie zwischen den einzelnen Individuen variieren und mit anderen qualitativen Merkmalen zusammenhängen. Eine auffällige Eierfärbung ist ein Merkmal, das sich durch sexuelle Selektion als ein Signal für die Qualität des Weibchens herausgebildet haben könnte. Diese Hypothese basiert auf der Annahme, dass das Pigment für blau-grüne Schalenfärbung möglicherweise eine begrenzte Ressource ist und es deshalb aufwendig wäre, diese für die Färbung von Eischalen zu verbrauchen. Für den Berghüttensänger (Sialia currucoides) untersuchten wir die mögliche Signalwirkung blau-grüner Schalenfärbungen durch die Quantifizierung der Farbmustervariationen innerhalb eines Geleges einerseits und andererseits zwischen einzelnen Gelegen, um herauszufinden, ob das Pigment begrenzt ist und ob bestimmte Farbmuster für individuelle Weibchen spezifisch sind. Über zwei Brutperioden hinweg untersuchten wir außerdem, ob es Zusammenhänge zwischen den Eierfärbungen und anderen Merkmalen der Weibchen und ihren “Investments” in die Eier gab. Innerhalb eines Geleges wiederholte sich das gleiche Farbmuster immer wieder und war ziemlich konsistent für Bruten in unterschiedlichen Jahren, was darauf hinweist, dass die Farbmuster der Eischalen ein intrinsisches Merkmal sind. Eier einer zweiten Brut in der gleichen Brutsaison zeigten eine weniger satte blau-grüne Farbgebung als in den ersten Bruten, und innerhalb eines Geleges waren die später gelegten Eier generell heller und blasser blau-grün als die vorher gelegten Eier, was auf einen begrenzten Pigment-Vorrat hindeutet. Aber mögliche Zusammenhänge zwischen der Schalenfärbung einerseits und anderen Merkmalen der Weibchen oder ihrer „Eier-Investments“waren weniger klar und über die Untersuchungsjahre hinweg widersprüchlich. Unsere Ergebnisse legen nahe, dass es ein Potential für blau-grüne Eifärbung als Signal für eine hohe Güte der Weibchen gibt; aber nur weitere Untersuchungen können letztlich zeigen, ob die blau-grüne Eifärbung wirklich ein Signal mit Informationswert ist.



We thank S. Proulx for allowing us access to his nest box trail, and L. James (James Cattle Company) and B. Twan (Alkali Lake Ranch) for allowing access to their properties. A. Lacika, S. Sparks, E. O’Brien, and E. Hancock provided assistance in the field, and the Hancock family provided key logistical support. We appreciate the constructive comments of D. Hanley and an anonymous reviewer on a previous version of the manuscript. Funding was provided by the Natural Sciences and Engineering Research Council of Canada, Canada Foundation for Innovation, British Columbia Knowledge Development Fund, and the University of Northern British Columbia. Our research protocols were approved by the University of Northern British Columbia Animal Care and Use Committee on behalf of the Canadian Council on Animal Care.

Compliance with ethical standards

Conflict of interest

The authors declare that there are no conflicts of interest.


  1. Andersson M (1994) Sexual selection. Princeton University Press, PrincetonGoogle Scholar
  2. Ardia DR (2005) Individual quality mediates trade-offs between reproductive effort and immune function in tree swallows. J Anim Ecol 74:517–524CrossRefGoogle Scholar
  3. Ardia DR, Wasson MF, Winkler DW (2006) Individual quality and food availability determine yolk and egg mass and egg composition in tree swallows Tachycineta bicolor. J Avian Biol 37:252–259CrossRefGoogle Scholar
  4. Baldauf SA, Bakker TC, Kullmann H, Thünken T (2011) Female nuptial coloration and its adaptive significance in a mutual mate choice system. Behav Ecol 22:478–485CrossRefGoogle Scholar
  5. Balenger SL, Johnson LS, Brubaker JL, Ostlind E (2007) Parental effort in relation to structural plumage coloration in the mountain bluebird (Sialia currucoides). Ethol 113:838–846CrossRefGoogle Scholar
  6. Cassey P, Ewen JG, Blackburn TM, Hauber ME, Vorobyev M, Marshall NJ (2008) Eggshell colour does not predict measures of maternal investment in eggs of Turdus thrushes. Naturwissenshaften 95:713–721CrossRefGoogle Scholar
  7. Cassey P, Mikšík I, Portugal SJ, Maurer G, Ewen JG, Zarate E, Sewell MA, Karadas F, Grim T, Hauber ME (2012) Avian eggshell pigments are not consistently correlated with colour measurements or egg constituents in two Turdus thrushes. J Avian Biol 43:503–512CrossRefGoogle Scholar
  8. Christians JK (2002) Avian egg size: variation within species and inflexibility within individuals. Biol Rev 77:1–26CrossRefPubMedGoogle Scholar
  9. Collias EC (1993) Inheritance of egg-color polymorphism in the village weaver (Ploceus cucullatus). Auk 110:683–692CrossRefGoogle Scholar
  10. Darwin C (1871) The descent of man, and selection in relation to sex. John Murray, LondonCrossRefGoogle Scholar
  11. Dearborn DC, Hanley D, Ballantine K, Cullum J, Reeder DM (2012) Eggshell colour is more strongly affected by maternal identity than by dietary antioxidants in a captive poultry system. Funct Ecol 26:912–920CrossRefGoogle Scholar
  12. Drent RH, Daan S (1980) The prudent parent: energetic adjustments in avian breeding. Ardea 68:225–252Google Scholar
  13. Edward DA, Chapman T (2011) The evolution and significance of male mate choice. Trends Ecol Evol 26:647–654CrossRefPubMedGoogle Scholar
  14. Hanley D, Doucet SM (2009) Egg coloration in ring-billed gulls (Larus delawarensis): a test of the sexual signaling hypothesis. Behav Ecol Sociobiol 63:719–729CrossRefGoogle Scholar
  15. Hargitai R, Herenyi M, Torok J (2008) Eggshell coloration in relation to male ornamentation, female condition and egg quality in the collared flycatcher Ficedula albicollis. J Avian Biol 39:413–422Google Scholar
  16. Honza M, Procházka P, Požgayová M (2012) Within and between season repeatability of eggshell coloration in the great reed warbler Acrocephalus arundinaceus. J Avian Biol 43:91–96CrossRefGoogle Scholar
  17. Hoyt DF (1979) Practical methods of estimating volume and fresh weight of bird eggs. Auk 96:73–77Google Scholar
  18. Johnsen A, Vesterkjær K, Slagsvold T (2011) Do male pied flycatchers (Ficedula hypoleuca) adjust their feeding effort according to egg colour? Ethol 117:309–317CrossRefGoogle Scholar
  19. Karubian J (2013) Female ornamentation in Malurus fairy-wrens: a hidden evolutionary gem for understanding female perspectives on social and sexual selection. Emu 113:248–258CrossRefGoogle Scholar
  20. Kodric-Brown A, Brown JH (1984) Truth in advertising: the kinds of traits favored by sexual selection. Amer Nat 124:309–323CrossRefGoogle Scholar
  21. Krist M, Grim T (2007) Are blue eggs a sexually selected signal of female collared flycatchers? A cross fostering experiment. Behav Ecol Sociobiol 61:863–876CrossRefGoogle Scholar
  22. Krištofík J, Darolová A, Griggio M, Majtán J, Okuliarová M, Zeman M, Zídkova L, Hoi H (2013) Does egg coloration signal female and egg quality in reed warbler (Acrocephalus scirpaceus). Ethol Ecol Evol 25:129–143CrossRefGoogle Scholar
  23. Lessells CM, Boag PT (1987) Unrepeatable repeatabilities: a common mistake. Auk 104:116–121CrossRefGoogle Scholar
  24. López de Hierro MDG, De Neve L (2010) Pigment limitation and female reproductive characteristics influence egg shell spottiness and ground colour variation in the house sparrow (Passer domesticus). J Ornithol 151:833–840CrossRefGoogle Scholar
  25. López-Rull I, Miksik I, Gil D (2008) Egg pigmentation reflects female and egg quality in the spotless starling Sturnus unicolor. Behav Ecol Sociobiol 62:1877–1884CrossRefGoogle Scholar
  26. Maia R, Eliason CM, Bitton PP, Doucet SM, Shawkey MD (2013) Pavo: an R Package for the analysis, visualization and organization of spectral data. Methods Ecol Evol 4:906–913Google Scholar
  27. McGraw KJ, Mackillop EA, Dale J, Hauber ME (2002) Different colors reveal different information: how nutritional stress affects the expression of melanin- and structurally based ornamental plumage. J Exp Biol 205:3747–3755PubMedGoogle Scholar
  28. Morales J, Sanz JJ, Moreno J (2006) Egg colour reflects the amount of yolk maternal antibodies and fledging success in a songbird. Biol Lett 2:334–336CrossRefPubMedPubMedCentralGoogle Scholar
  29. Morales J, Kim S-Y, Lobato E, Merino S, Tomás G, Martinez-de la Puente J, Moreno J (2010) On the heritability of blue-green eggshell coloration. J Evol Biol 23:1783–1791CrossRefPubMedGoogle Scholar
  30. Morales J, Velando A, Torres R (2011) Biliverdin-based egg coloration is enhanced by carotenoid supplementation. Behav Ecol Sociobiol 65:197–203CrossRefGoogle Scholar
  31. Moreno J, Osorno JL (2003) Avian egg colour and sexual selection: does eggshell pigmentation reflect female condition and genetic quality. Ecol Lett 6:803–806CrossRefGoogle Scholar
  32. Moreno J, Osorno JL, Morales J, Merino S, Tomas G (2004) Egg coloration and male parental effort in the pied flycatcher Ficedula hypoleuca. J Avian Biol 35:300–304CrossRefGoogle Scholar
  33. Moreno J, Morales J, Lobato E, Merino S, Tomas G, Martinez-de la Puente J (2005) Evidence for the signaling function of egg color in pied flycatcher Ficedula hypoleuca. Behav Ecol 16:931–937CrossRefGoogle Scholar
  34. Moreno J, Lobato E, Morales J, Merino S, Tomas G, Martinez-de la Puente J, Sanz JJ, Mateo R, Soler JJ (2006) Experimental evidence that egg color indicates female condition at laying in a songbird. Behav Ecol 17:651–655CrossRefGoogle Scholar
  35. Morrison A, Flood NJ, Reudink MW (2014) Reproductive correlates of plumage coloration of female Mountain Bluebirds. J Field Ornithol 85:168–179CrossRefGoogle Scholar
  36. Navarro C, Perez-Contreras T, Aviles JM, McGraw KJ, Soler JJ (2011) Blue-green eggshell coloration reflects yolk antioxidant content in spotless starlings Sturnus unicolor. J Avian Biol 42:538–543CrossRefGoogle Scholar
  37. O’Brien EL, Dawson RD (2013) Experimental dissociation of individual quality, food and timing of breeding effects on double-brooding in a migratory songbird. Oecol 172:689–699CrossRefGoogle Scholar
  38. O’Brien EL, Dawson RD (2011) Plumage color and food availability affect male reproductive success in a socially monogamous bird. Behav Ecol 22:66–72CrossRefGoogle Scholar
  39. Peak B (2011) The white bluebird egg phenomenon. Bluebird 33:16–19Google Scholar
  40. Power HW, Lombardo MP (1996) Mountain Bluebird (Siala currucoides). In: Poole A (ed) The birds of North America online. Ithaca (NY), Cornell Lab of OrnithologyGoogle Scholar
  41. R Core Team (2014) R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. URL: Accessed 20 Aug 2017
  42. Randall JA (2016) Causes and consequences of blue-green eggshell colour variation in mountain bluebirds (Sialia currucoides). University of Northern British, ColumbiaCrossRefGoogle Scholar
  43. Randall JA, Dawson RD (2017) Incubation and embryonic development affect the color of eggs of Mountain Bluebirds. J Field Ornithol 88:198–205CrossRefGoogle Scholar
  44. Schaalje GB, McBride JB, Fellingham GW (2001) Approximations to distributions of test statistics in complex mixed linear models using SAS Proc MIXED. SAS User’s Group Int 26:262Google Scholar
  45. Siefferman L, Hill GE (2005) Evidence for sexual selection on structural plumage coloration in female eastern bluebirds (Sialia sialis). Evolution 59:1819–1828CrossRefPubMedGoogle Scholar
  46. Siefferman L, Navara KJ, Hill GE (2006) Egg coloration is correlated with female condition in eastern bluebirds (Sialia sialis). Behav Ecol Sociobiol 59:651–656CrossRefGoogle Scholar
  47. Soler JJ, Navaro C, Contreras TP, Aviles JM, Cuervo JJ (2008) Sexually selected egg coloration in spotless starlings. Amer Nat 171:183–194CrossRefGoogle Scholar
  48. Sparks NH (2011) Eggshell pigments—from formation to deposition. Avian Biol Res 4:162–167CrossRefGoogle Scholar
  49. Stocker R, McDonagh AF, Glazer AN, Ames BN (1990) Antioxidant activities of bile pigments: biliverdin and bilirubin. Methods Enzymol 186:301–309CrossRefPubMedGoogle Scholar
  50. Trivers RL (1972) Parental investment and sexual selection. In: Campell B (ed) Sexual selection and the descent of man. Aldine Publishing Company, Chicago, pp 136–179Google Scholar
  51. Vitousek MN, Dor R, Safran RJ (2012) Sexual signaling: climatic carry-over. Curr Biol 22:R61–R63CrossRefPubMedGoogle Scholar
  52. von Schantz T, Bensch S, Grahn M, Hasselquist D, Wittzell H (1999) Good genes, oxidative stress and condition dependent signals. Proc R Soc B 266:1–12CrossRefGoogle Scholar
  53. Weiss SL (2006) Female-specific color is a signal of quality in the striped plateau lizard (Sceloporus virgatus). Behav Ecol 17:726–732CrossRefGoogle Scholar
  54. Wiebe KL, Bortolotti GR (1995) Egg size and clutch size in the reproductive investment of American kestrels. J Zool L 237:285–301CrossRefGoogle Scholar
  55. Zahavi A (1975) Mate selection—selection for a handicap. J Theor Biol 53:205–214CrossRefPubMedGoogle Scholar
  56. Zhao R, Xu G-Y, Liu Z-Z, Li J-Y, Yang N (2006) A study on eggshell pigmentation: biliverdin in blue-shelled chickens. Poult Sci 85:546–549CrossRefPubMedGoogle Scholar

Copyright information

© Dt. Ornithologen-Gesellschaft e.V. 2017

Authors and Affiliations

  1. 1.Ecosystem Science and Management ProgramUniversity of Northern British ColumbiaPrince GeorgeCanada

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