Ultraviolet colour variation influences blue tit sex ratios

@article{Sheldon1999UltravioletCV,
  title={Ultraviolet colour variation influences blue tit sex ratios},
  author={Ben C. Sheldon and Staffan Andersson and Simon C. Griffith and Jonas {\"O}rnborg and Joanna Sendecka},
  journal={Nature},
  year={1999},
  volume={402},
  pages={874-877}
}
Brilliant blue and violet structural colours are common plumage ornaments in birds, but their signalling functions are poorly understood. This may be because birds also communicate in ultraviolet (UV-A) wavelengths (320–400 nm), invisible to humans, but a strong spectral component of many structural colours. From a wild population of blue tits—Parus caeruleus, sexually dimorphic primarily in the ultraviolet—we report experimental evidence that females skew the sex ratio of their offspring in… 
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