OYSTERCATCHER AND NATURAL ENVIRONMENT. 285 



good size on the mud. The central area slopes more steeply 

 downwards where it borders the channel so that, when the tide 

 is out, the birds can feed without being readily seen from the 

 land. The feeding area is more than 150 metres from the grass. 

 The central portion of the sandbar does not cover at high water, 

 when it is used as a refuge. There is a moderate stock of 

 Oystercatchers. 



3. Rock-beach, Mud-flat Habitat. — A. Aberlady Station. Aber- 

 lady Bay is a large sandy and muddy flat, intersected by the 

 channel of the Peffer Burn. The bay may be divided into three 

 transverse zones. The highest zone is rarely visited by Oyster- 

 catchers. The middle zone, west of the channel, is a mud-flat. 

 The mud is tenacious and does not shift readily. The greater 

 part of the area is covered with Mussels of a good size, and is 

 more than 150 metres from the nearest danger point. Eastward 

 of the channel the conditions are, at first, similar to those of the 

 western part of the middle zone, but they soon change to a sand- 

 beach, which extends to the eastern high- water mark. The 

 lower zone is composed mainly of sand-flats, which become 

 extensive as the bay widens towards its outlet. In the middle 

 zone, with the exception of the steep borders of the channel, the 

 substratum lies mostly above mean-water level. In Gosford Bay 

 is a large smoothly contoured area of volcanic rock. Mytilus is 

 abundant here and of fair size. The mud in the lower part of the 

 bay is apt to shift and bury the lower lying Mussels. East of these 

 rocks a sandy bay is a factor of some importance. The rocks at 

 the east and west ends of Gosford Bay are loaded with Fucus. At 

 the east end of Longniddry Bay is a 1 stretch of low-lying volcanic 

 rocks, well provided with Mussels. These rocks, though lying 

 rather near the high-water mark, are covered early by the 

 incoming tide. The volcanic rocks east of Gullane Point have 

 considerable supplies of Mussels. These rocks alternate with 

 sand-beaches. They lie close in to the shore generally, and 

 through their conformation are easily approached. One part 

 extends far out into the sea, but the non-tidal portion runs 

 nearly as far, and is well adapted for stalking. The area is 

 visited irregularly by Oystercatchers. The refuge for this 

 station is nearly five kilometres distant (Eyebroughty). The 

 resident stock is, perhaps, the largest in the Forth. The birds 



