OYSTERCATCHER OR SEAPIE 403 



When the ebb leaves the scalps dry and the majority of the 

 mussels are invulnerable owing to the closing of the shells, there 

 are still available those few whose ventral surfaces are exposed. The 

 oystercatchers appear then to divide the time until the tide turns 

 between searching for these latter, hunting for suitably placed 

 mussels under the wet edges of the bank, in pools, and also for 

 those covered with sand or mud. The oystercatcher finds buried 

 mussels by a process of tapping the surface of the ground with the 

 tip of its bill. "At first the ground is tapped here and there in 

 tentative fashion. Sometimes a single tap leads directly to the 

 mussel ; more often numerous taps are made in a small area until 

 one is made in the right place." The oystercatcher then sinks its 

 bill quickly into the sand, and deals with the mussel in much the 

 same way as when they are exposed on the banks. Mr. Dewar 

 states that more mussels are opened by way of the ventral borders 

 when buried than when exposed. It is difficult to see why this 

 should be, unless it is that the mussels, when buried, are less likely 

 to occupy their normal position. 



When the tide has receded far enough to enable the oyster- 

 catchers to work on the banks, they may be seen walking sedately 

 about searching for slightly gaping shells. They carry their heads 

 well forward and their bills in a position ready to strike. 



Each mussel is approached in the line of its major axis, and is 

 submitted to a careful inspection, usually from the front. If the 

 mussel meet with approval, the oystercatcher strikes a sharp blow 

 with the point of its bill on the summit of the dorsal border, 

 apparently to find out whether or not the bill will pass between 

 the edges of the valves. When the result of the tap is favourable, the 

 bill is pushed down into the mussel before the valves have time to 

 close, by a number of jerks with great rapidity and force, and the 

 shells are finally separated by various levering methods described in 

 detail by Mr. Dewar. 



Similar methods obtain in opening mussels through the ventral 



VOL. in. 



