OYSTERCATCHEB AND NATURAL ENVIRONMENT. 379 



summer environment. In all the other stations, with the 

 exception of Clunie, where eggs have not been known to hatch, 

 a local feeding-ground is present, and may, therefore, be 

 regarded as having great ecological value. 



The most valuable conditions of the local feeding-ground are 

 the presence of a large stock of tipulid and beetle larvae, and 

 comparative freedom from human intrusion. The conditions are 

 best fulfilled by fenced-in old pastures. Ground of this nature 

 is attached to most of the breeding areas. On the Orchy, 

 however, it is absent, and the grassy river-bank takes its place. 

 The great value of an area of old turf is made evident by the 

 history of the Dunavourd territory, where the breeding territory 

 ceased to be occupied whenever the old pasture was ploughed. 

 Occasionally arable land forms the local feeding-ground. In the 

 middle Logerait settlement, and on a shingle island in the Eiver 

 Lyon near Chesthill, wooded islands are the only available local 

 feeding-grounds. The upper island at Logerait and the island 

 at. Chesthill are apparently of natural origin, and provide 

 a different food supply for the young from that occurring in the 

 normal feeding-ground. The fauna of the ground strata of the 

 naturally wooded islands appears to be that of the flood-plain 

 forest association. 



The third area of a favourable station — the general or 

 distant feeding- ground — has, as its chief functions, the feeding 

 of the adults and the supply of large earthworms for the young. 

 For the latter purpose cultivated land is best adapted. Cultivated 

 land adjoins all the breeding areas of the Tummel, Garry and 

 Fender. Under certain conditions (e.g. drought) the young 

 receive very little food from farm land. Arable soil is practically 

 absent from Upper Glenlyon, and from Glenorchy above the 

 Bridge of Orchy. It is, therefore, not essential. But the distri- 

 bution of the birds shows that, wherever the unproductive hill- 

 side takes the place of cultivated land, a much larger area is 

 required to support the same number of birds. The occurrence 

 of cultivated land in the environment is, of course, a secondary 

 condition. It is possible the distribution of the boulder clay, 

 and especially its presence on south-western exposures, favoured 

 the settlement of the earthworm, and thus effected a primitive 

 control over the distribution of the Oystercatcher population, 



2 g 2 



