igS SEA-BIRDS 



or in small parties; but they may roost communally. In flight there 

 are no very closely co-ordinated movements as in flocks of shearwaters, 

 waders and starlings. But when a shoal of fish is sighted numbers 

 come together in one spot and there may be all the appearance of 

 co-ordinated action. The little black cormorant {Phalacrocorax sulcirostris) 

 and the white pelican {Pelecanus erythrorhynchos) have a communal 

 method of fishing. They gather in large companies and fly in long 

 columns until a shoal is encountered; the leading birds wheel round, 

 settle on the water, and proceed to concentrate the shoal by an ever- 

 narrowing circling movement — diagram A (Serventy, 1939). The 

 guanay cormorant ( P. bougainvillii ) actually appears to send out 

 scouts, which indicate prey as vultures do. 



Fig. 34 

 Path of fishing cormorants; A: after Serventy (1939) ; B: after Steven (1933) 



Steven ( 1933) observed that a single shag rounded up a shoal of 

 sand-eels, then fed as it swam through the centre of concentration — 

 diagram B. Taverner (1934) says that double-crested cormorants 

 (P. auritus) will spread themselves across the mouth of a bay, and 

 make a drive towards a common centre. The scene becomes more and 

 more animated as the fish are congested in shallow water. The divings 

 become shorter and more rapid, and more fish are tossed and swallowed 

 in hurried haste for the next beakful. At last the surviving fish make 

 a despairing rush through the ranks of their enemies. The birds 

 then form lines again along another section of the water to repeat 

 the operation. Some of these rafts may consist of 1,800 to 2,000 

 individuals. 



Where cormorants and pelicans fish together the more agile cor- 

 morants will steal fish in front of the open scoop-like bill of the pelicans 

 which are greedily filling their huge pouches; and the brown pelican 

 has a pouch capacity of 3^^ gallons. The man-o'-war bird Fregata 

 magnijicens, which is expert at snatching fish from the mouth of the 



