Nolan, P. M., Dobson, F. S., Nicolaus, M., Karels, T. J., Mcgraw, K. J., & Jouventin, P. (2010). Mutual mate choice for colorful traits in King Penguins. Ethology, 116(7), 635-644. doi:10.1111/j.1439-0310.2010.01775.x.