OYSTEBCATCHEB AND NATUBAL ENVIBONMENT. 883 



for the young. Occasionally, young have been seen to manifest 

 signs of more than passing hunger owing to the drought-induced 

 dearth of earthworms and the difficulty of getting other supplies. 

 But in no observed instance have the young appeared to suffer 

 permanently in consequence of the shortage. 



VI. — The Choice of a Nesting- Site. 

 In the choice of a nesting-site which is placed near a body 

 of water, an important factor must be the relation existing 

 between the position of the nest and the level of the water at 

 the time of building, and any possible rise in the level of the 

 water during the subsequent period of laying and incubation. 

 In the river-valley habitat the nests are formed on the highest 

 part of the banks of shingle, and in the case of the semilunar 

 beds, which form on the convexities of the alluvial cones, the 

 nests are laid on the longitudinal ridge which has formed in the 

 shingle, a short distance from the grass bank. In the lake- 

 shore habitat, as represented by Loch Tummel, the problem 

 does not appear to be so simple. The beach of the alluvial 

 cones has, for the most part, an even gradient from the water- 

 edge up to the grass. The nests, as a rule, are formed on, or 

 about, the highest winter water-mark. But in places the mark 

 is not evident, and apparently is not detected by the birds. In 

 other parts the high-level mark reaches up over the grass. 

 Where this happens, the nests are formed on the shingle within 

 a half to one metre of the bank. It is probable that, in the 

 choice of a nesting-site in this locality, the adjustment of the 

 bird to the environment is more perfect at the normal period of 

 laying than it is at a later time. This may be put in another 

 way by saying that the normal period of laying occurs at 

 a time when the level of the loch is already low and still 

 falling. At a later period the loch is either at bottom level 

 or has actually begun to rise. At the former period the 

 choice of a nesting-site is stereotyped, appropriate to the 

 local conditions, and successful. At the later period the birds 

 respond with the stereotyped reaction to conditions which 

 are essentially, though not obviously, different from the 

 normal, and which day by day may depart still further from 

 the normal. 



(To be continued.) 



