OYSTERCATCHER OR SEAPIE 401 



now throughout the autumn and winter large flocks may be seen on 

 the coasts, especially where there are large mussel-beds. In the 

 west of Scotland the flocks often number one hundred or more birds. 

 When disturbed whilst resting, these generally break up into two or 

 three smaller companies, each apparently with a leader who acts as 

 guide. 1 



Although, as before stated, the oystercatcher's diet is a varied 

 one, yet it feeds very largely on shellfish, more especially mussels, as 

 the fact that its bill is specially modified for opening the shells would 

 indicate. Moreover, it has been shown by careful observation, as set 

 forth in a most exhaustive treatise by Mr. J. M. Dewar, 2 that, apart 

 from the specialised form of its bill for gaining entrance through the 

 shell, the oystercatcher employs deliberate method, varying with the 

 position of the mussel, to secure the contents, skilfully removing 

 " certain structures which hinder the achievement of its desires." 

 The oystercatcher being a most wary bird, and its feeding-grounds, 

 as a rule, very exposed and open, close observation of its habits while 

 feeding is attended with unusual difficulties, and requires consider- 

 able patience. By supplementing his observations of the birds whilst 

 engaged on the scalps with an examination of the empty shells, Mr. 

 Dewar was able to give some interesting statistics. Of the shells 

 opened by the oystercatchers, it was found that approximately 78 per 

 cent, were opened through the dorsal border, 9 per cent, through the 

 ventral border, and about 13 per cent, through the posterior end. 

 The preponderance of the first form is due to the fact that in their 

 normal position on the banks the mussels present their dorsal borders. 

 These are practically invulnerable, except when the valves are slightly 

 separated, and this the mussel's attitude of rest is " possible only 

 when the shells are under water, or in moist situations." If dry the 

 mussels must close their valves, or the delicate internal structures 

 w r ould shrivel. Fresh water has the same effect as dryness ; heavy 



1 Gray, Birds of the West of Scotland, p. 270. 



2 Zoologist, 1908, pp. 201-212, from which all the details relating to the feeding habits of the 

 oystercatcher are culled. 



