370 THE ZOO LOO 1ST. 



THE EELATION OF THE OYSTEEGATCHEE TO ITS 

 NATUEAL ENVIEONMENT. 



By J. M. Dewar, M.D. 



(Continued from p. 346.) 



V. — Discussion of the Summer Environment. 



The conditions common to most of the stations of the 

 summer habitats are the following : a body of fresh water, a 

 breeding area of water-worn shingle, composed of light grey 

 stones of medium or small size, the area being adjacent to water, 

 raised above the level of summer floods, and fairly well-preserved 

 from human intrusion ; a local feeding-ground to which there is 

 easy access for the young on foot, rich in tipulid and coleopter- 

 ous larvae, and with at least a moderate supply of large earth- 

 worms ; a more distant feeding-ground of cultivated land, accessi- 

 ble to the adults, and richly stocked with large earthworms. 



The first condition is an essential requirement and is used in 

 many ways, of which the act of drinking is only one. Both the 

 adults and the young bathe in the water, and stand in it by the 

 hour. A large still body of water, or a narrow deep or quickly 

 flowing stream, safeguards one border of the breeding area from 

 intrusion, and favours the detection of approaching danger. 

 The young in danger frequently crouch in shallow water among 

 stones, and in the last resort swim boldly out on the open lake 

 or across narrow and not too rapid streams. In the river 

 settlements especially, a portion of the food supply for the 

 young is got from the shallow waterside. 



Shingle does not form a necessary condition of the breeding 

 area. It is absent from North Holland where the birds nest 

 commonly on areas of grey mud, as do most of the birds in the 

 Moulinearn Settlement, while at Ballinluig nesting on turf under 

 trees is common. On shingle, however, the eggs and young are 

 incomparably harder to find than on any other substratum used 



