Abstract
In spite of strong evidence for viability-based sexual selection and sex ratio adjustments, the blue tit, Parus caeruleus, is regarded as nearly sexually monomorphic and no epigamic signals have been found. The plumage coloration has not, however, been studied in relation to bird vision, which extends to the UV-A waveband (320 to 400 nm). Using molecular sex determination and UV/VIS spectrometry, we report here that blue tits are sexually dichromatic in UV/blue spectral purity (chroma) of the brilliant crown patch. It is displayed in courtship by horizontal posturing and erected nape feathers. A previously undescribed sexual dimorphism in crown size (controlling for body size) further supports its role as an epigamic ornament. Against grey-brown leaf litter and bark during pair formation in early spring, but also against green vegetation, UV contributes strongly to conspicuousness and sexual dimorphism. This should be further enhanced by the UV/bluish early morning skylight ('woodland shade') in which blue tits display. Among 18 breeding pairs, there was strong assortative mating with respect to UV chroma, but not size, of the crown ornament. We conclude that blue tits are markedly sex dimorphic in their own visual world, and that UV/violet coloration probably plays a role in blue tit mate acquisition.
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Selected References
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- Bennett A. T., Cuthill I. C., Partridge J. C., Lunau K. Ultraviolet plumage colors predict mate preferences in starlings. Proc Natl Acad Sci U S A. 1997 Aug 5;94(16):8618–8621. doi: 10.1073/pnas.94.16.8618. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Bennett A. T., Cuthill I. C. Ultraviolet vision in birds: what is its function? Vision Res. 1994 Jun;34(11):1471–1478. doi: 10.1016/0042-6989(94)90149-x. [DOI] [PubMed] [Google Scholar]
- Bowmaker J. K., Heath L. A., Wilkie S. E., Hunt D. M. Visual pigments and oil droplets from six classes of photoreceptor in the retinas of birds. Vision Res. 1997 Aug;37(16):2183–2194. doi: 10.1016/s0042-6989(97)00026-6. [DOI] [PubMed] [Google Scholar]
- Chen D. M., Goldsmith T. H. Four spectral classes of cone in the retinas of birds. J Comp Physiol A. 1986 Oct;159(4):473–479. doi: 10.1007/BF00604167. [DOI] [PubMed] [Google Scholar]
- Ellegren H. First gene on the avian W chromosome (CHD) provides a tag for universal sexing of non-ratite birds. Proc Biol Sci. 1996 Dec 22;263(1377):1635–1641. doi: 10.1098/rspb.1996.0239. [DOI] [PubMed] [Google Scholar]
- Goldsmith T. H. Optimization, constraint, and history in the evolution of eyes. Q Rev Biol. 1990 Sep;65(3):281–322. doi: 10.1086/416840. [DOI] [PubMed] [Google Scholar]
- Goldsmith T. H. Ultraviolet receptors and color vision: evolutionary implications and a dissonance of paradigms. Vision Res. 1994 Jun;34(11):1479–1487. doi: 10.1016/0042-6989(94)90150-3. [DOI] [PubMed] [Google Scholar]
- Maier E. J. Ultraviolet vision in a passeriform bird: from receptor spectral sensitivity to overall spectral sensitivity in Leiothrix lutea. Vision Res. 1994 Jun;34(11):1415–1418. doi: 10.1016/0042-6989(94)90141-4. [DOI] [PubMed] [Google Scholar]
- Osorio D., Bossomaier T. R. Human cone-pigment spectral sensitivities and the reflectances of natural surfaces. Biol Cybern. 1992;67(3):217–222. doi: 10.1007/BF00204394. [DOI] [PubMed] [Google Scholar]
- doi: 10.1098/rspb.1997.0221. [DOI] [PMC free article] [Google Scholar]
- doi: 10.1098/rspb.1998.0316. [DOI] [PMC free article] [Google Scholar]