GULLS 113 



thrown up, nothing is left to show that the bird 

 has fed on fish. 



From what I have written it will be realised 

 that the rate of digestion in gulls must be allowed 

 for when one considers their influence on fish 

 life. 



The presence of otoliths, or ear bones, in the 

 gizzard of a gull is also a means of estimating 

 the number of fish taken by this bird. In many 

 bony fishes there is, on either side of the base 

 of the cranial cavity, a sac which contains an 

 otolith, or ivory-hard ear bone. The margins 

 are indented and the surface is grooved. In 

 these grooves are lodged the terminations of the 

 nerves connected with hearing. 



Otoliths vary greatly in size and shape, but 

 they are distinctive in various fish. In conse- 

 quence of their hardness they resist the tritura- 

 ting action in the gizzard of the gull, and remain 

 long after the soft bones have disappeared. 

 Speaking generally, an average-sized otolith is 

 rendered quite smooth and very much diminished 

 in size in twelve hours, and has disappeared in 

 twenty-four. 



I will now give an example of the value of 

 otoliths and the air vesicles described in estimat- 



