From a fascinating writeup about the cowbird:

“The interior of a bluebird nestlings’ mouth is yellow. A cowbird nestling has a deep pink or cherry red mouth. Apparently an indicator that a nestling has not been fed recently is blood collected around the mouth. After the baby is fed, blood is drawn to the digestive area, and the color of the mouth fades. Thus having a bright red mouth, and the ability (due to earlier hatching and larger size) to reach higher when gaping results in Cowbird nestlings receiving priority for feeding. Also, Cowbird’s eyes open around Day 2 (about 4 days earlier than a bluebird nestling), so they are better equipped to detect the presence of their adopted parents and position and beg more effectively to receive priority for feeding.”
Posted by JRM on Sat, 28 Jan 2006 22:58 | #
It has come to the attention of the authorities that you have been making implicit analogies between the behavior of humans and the behavior of animals. This pathology of generalizing behavior across realms must stop. Theories of resource competition and parasitism DO NOT apply to humans because humans are EXEMPT from selection. That’s why we all get along with one another.