io6 ANIMAL LIFE UNDER WATER 



ing in a similar manner they were doing most 

 useful work. 



On another occasion, at the invitation of a 

 representative of the Essex and Suffolk Fishery 

 Board, I went to the River Aide, where the 

 black-headed gulls were described as plunging 

 below the water after fish. These birds certainly 

 did disappear below the surface, but when 

 examined they were found to be full of shrimps 

 (Crangon vulgaris). 



Again, gulls have often been examined in 

 the vicinity of fisheries, and it has been found 

 that here they merely pick up the fish thrown 

 overboard, and really act as scavengers. 



On the other hand, the fact that a gull does 

 not contain any apparent traces of fish when 

 examined is no indication that it has not 

 devoured several during the day. Even a small 

 bird, such as the black-headed gull, can digest 

 a six-inch fish within four hours so completely 

 as to leave no trace of it throughout the alimen- 

 tary tract. Further, gulls are omnivorous and 

 voracious feeders, and often exceptional feeding 

 habits are quoted as evidence of the good or 

 bad influence they have on fish fife, agricul- 

 ture, etc. 



