2S2 THE ZOOLOGIST. 



the River Garry below the village of Blair and in Glen Fender, all 

 of which are in North Perthshire, during the summers 1909 to 

 1914 inclusive. The former represent the winter environment ; 

 the latter a summer environment of the Oystercatcher, no data 

 being here included from the coastal breeding stations. Observa- 

 tions of a less continuous character were made in other localities 

 as a means of control. No attempt was made to work out the 

 local distribution in either the summer or the winter area, or to 

 obtain experimental control of any environmental factors.* 



On the Firth of Forth localities were noted where Oyster- 

 catchers were found to occur. By repeated observations it 

 was ascertained whether the places were in permanent winter 

 occupation or not. In the former case, the number of occupants 

 was periodically estimated, and the environmental conditions 

 were, as far as possible, discovered. Mytilus edulis was accepted 

 as the chief food supply of the Oystercatcher. Where the birds 

 were occasional visitors to important stations of Mytilus, or did 

 not occur at all, the stations were regarded as potential Oyster- 

 catcher stations, and their conditions found. Two chief types 

 of habitats were recognized on the sea-beach. These were com- 

 pared intensively, in order to determine which might be the 

 more favourable to the Oystercatcher. 



In the summer environment three habitats were separated. 

 The number of pairs per linear measure of loch, river, and hill- 

 stream was used to determine the most favourable habitat. The 

 conditions of all likely or occupied breeding- stations under 

 observation were noted and compared to find those common to 

 all the stations, those present only in the more favourable 

 stations, and those awanting at potential stations. The results 

 derived from the individual stations were then aggregated for 

 the several habitats, and the conditions of the most suitable 

 habitat discovered. 



II. — The Winter Environment. 



1. General Considerations. — The northern shore of the Firth 

 of Forth, below the Forth Bridge, generally descends steeply into 



* Valuable information on the areas under observation was obtained 

 from tbe 'Memoirs of the Geological Survey of Scotland,' Nos. 32, 33, and 

 55 ; Appendix III. to the ' Weekly Weather Eeport ' for 1908 ; the Admiralty 

 Charts and Manual, 



