GULLS in 



tions are appreciated as sound, and in order that 

 the anterior air vesicles may make a better 

 sounding-box, the bone around has become 

 denser. 



It is this harder bone that resists the triturat- 

 ing action in the gizzard of the gull long after 

 the softer bones have disappeared. As stated, 

 the presence of a bony globule floating on the 

 surface when the contents of a gull are washed 

 out is a sure sign that the bird has taken a 

 member of the herring family during the day. 



To return to an examination of the contents 

 of the six other black-headed gulls that had taken 

 blued sprats. The second bird contained sixteen 

 spicules of bone, the remains' of almost digested 

 vertebrae and two air vesicles. The third and 

 fourth birds revealed fish in the gullet, as shown 

 on the plate opposite page 110. The fish had 

 been rendered soft and pulpy by the gastric 

 juices, and fell to pieces in the fingers — each fish 

 contained methylene blue. The explanation in 

 the different rate of digestion is as follows : In 

 the first two birds the gizzards were empty when 

 they took the prepared sprats, and so the fish 

 passed down to be triturated; but the third and 

 fourth birds had fed on the refuse heap before 



