Casagrande, S., Costantini, D., Tagliavini, J., & Dell’Omo, G. (2008). Phenotypic, genetic, and environmental causes of variation in yellow skin pigmentation and serum carotenoids in Eurasian kestrel nestlings. Ecological Research, 24(2), 273-279. doi:10.1007/s11284-008-0503-3.