44 THE ZOOLOGIST. 



also hammered, and the blows are delivered into the hiatus in 

 the border of the shell. That this should be so in the absence 

 of any apparent necessity to hammer is peculiar, but it probably 

 represents the continuity of a habit fixed for the time being. 

 The hammering method has two advantages and a number of 

 drawbacks. It is a rapidly and fairly assured way of getting 

 food. The birds may be seen to rush from one shell to another, 

 hammer each one open in turn, lever the valves apart if neces- 

 sary, and wolf the contents. In three minutes a single bird 

 opened and cleared twenty-six shells, varying from one inch to 

 three-quarters of an inch in length. Another worked at an 

 average rate of seven to eight shells per minute, the shells 

 varying from seven-eighths to five-eighths of an inch in length. 

 It maintained this speed for three-quarters of an hour, and con- 

 tinued to open shells, though less quickly, for another quarter 

 of an hour. Thus it must have cleared the contents of upwards 

 of four hundred shells in one hour. The drawbacks are con- 

 siderable, but they evidently do not outweigh the advantages of 

 rapidity and comparative certainty. The output of energy is 

 enormous. One can scarcely doubt that the birds are making 

 violent exertions, and, though a small amount of visual selection 

 is exercised over the sizes of the shells as the birds hurry from 

 one to another, yet a considerable proportion of the shells 

 successfully resists the hammering, and the birds have, per- 

 force, to pass on to others. As a rule, five to eight strokes with 

 the point of the bill are sufficient to perforate the shell. In one 

 case the bird returned three times, making four attacks alto- 

 gether on a single shell. Each attack consisted of twenty to 

 thirty powerful blows, making some eighty strokes in all, before 

 the onslaught met with success. In another, the bird ham- 

 mered five or six times without result. At once pressing the 

 point of ihe bill firmly and obliquely on the summit of the 

 shell, it walked round through quarter of a circle, and in its 

 new position applied several thrusts downwards. Still keeping 

 up pressure, it walked back to its old position and hammered 

 seven or eight times, the last stroke sending the bill deeply into 

 the shell. In other cases the hammering was preceded by firm 

 pressure of the point of the bill on the summit of the shell for 

 a few seconds with, at the same time, vigorous shaking of the 



