156 A HISTORY OF BIRDS 



the long white inner secondary quill feathers. The head, 

 meanwhile, is drawn down on to the pouch, while the long, 

 spike-like feathers which normally project backwards on either 

 side of the head now stand erect like a row of slender palisades 

 on each side of the partly hidden beak. Behind the head is a 

 great billowy mass of white feathers formed by the under-tail 

 coverts, and brought into view by the overturning of the tail 

 feathers. The feathered contortionist having completed this 

 complex series of movements, now stands solemnly facing his 

 mate, uttering now and again a low grunt like " oak, oak, 

 oak!" and then slowly returns to his normal shape again. 



Of the display of the Adjutant Stork there appears to be 

 no record. But this bird is provided with a pouch in some 

 respects more peculiar than that of the Bustards, inasmuch as 

 it can be filled and emptied with remarkable rapidity. Deflated 

 it is hardly visible, but may be detected in the shape of a 

 conical swelling of bare skin in front of the neck. Suddenly 

 it shoots out, or rather downwards, in the form of a large, naked 

 wind-bag of considerable size, and again disappears with magical 

 rapidity. This sac is filled through the naso-pharyngeal system, 

 that is, from air-sacs opening into the nose. How that of the 

 Great Bustard is filled is, by the way, unknown. 



II. Tournaments 



During the time that birds are under the stimulus of sexual 

 excitement mutual jealousies, leading to more or less vio- 

 lent encounters between rivals, are common among all species. 

 But there are some species which, of set purpose, appear to 

 gather together for the purpose of " sparring," apparently by way 

 of displaying their prowess in the presence of the females, but 

 without any desire to come to actual blows, though this oc- 

 casionally happens. These fight unarmed. On the other 

 hand, there are several species, especially among the Game- 

 birds, the Plover tribe and the Anatidae, which have developed 

 formidable weapons of offence, and these are used in deadly 

 earnest on every possible opportunity, at any rate during the 

 period now under discussion. There is, however, no hard and 

 fast line between these harmless encounters and duels to the 

 death, as we shall presently show. 



