American Kestrel (Falco sparverius) Science Article 6
Bright coloration in birds is typically a sexually selected trait. Expression of suchtraits is sensitive to environmental factors, so they can function as bioindicators ofenvironmental contamination. Of particular value may be carotenoid-based colorationbecause it is commonly used as a social signal and these pigments have importanthealth functions.
GARY R. BORTOLOTTI et al., Functional Ecology 2003 17, 651-657