Iris colour of American kestrels varies with age, sex, and exposure to PCBs.

@article{Bortolotti2003IrisCO,
  title={Iris colour of American kestrels varies with age, sex, and exposure to PCBs.},
  author={Gary R. Bortolotti and Judit E. G. Smits and David M. Bird},
  journal={Physiological and biochemical zoology : PBZ},
  year={2003},
  volume={76 1},
  pages={99-104}
}
For most species of birds, little is known about the pattern and significance of intraspecific variation in iris colour. In early winter, captive American kestrels could be subjectively placed into at least two age categories: 0.5-yr-old birds had all-brown irides, whereas those of older birds were red-brown. As part of a toxicological study on kestrels, we… CONTINUE READING