Head flagging in the Black-headed Gull; Its function and origin review

(Dept. of Zoology, Oxford University) STUDIES of the reproductive behaviour of various birds and fish have led to the conclusion that many elements of courtship, threat, and other types of display are " derived " movements. Some of these, such as the pecking gestures by which a Domestic Cock calls the hens to food, or the " strutting " postures of courting gallinaceous birds, have doubtless originated...