Advice on choosing a mate, from News of the Weird

According to Spanish biologist J.J. Negro (Estacion Biologica de Donana), reporting in the journal Nature in April, male Egyptian vultures compete for females on the basis of how brightly yellow the males’ faces are, and that brightness varies directly with the amount of excrement they eat. Cartenoids in dung produce the yellow around the vultures’ eyes, and only the strongest vultures can safely eat enough bacteria-laden feces to get a rich color.