426 THE ZOOLOGIST. 



THE RELATION OF THE OYSTERCATCHER TO ITS 

 NATURAL ENVIRONMENT. 



By J. M. Dewak, M.D. 



(Continued from p. 383.) 



In North Perthshire the average monthly rainfall shows a 

 progressive increase in amount through April, May, and June, 

 the first being the driest month of the year. In April and May 

 the rainfall tends to be evenly distributed over each month, and 

 the water is largely absorbed by the soil. In June the greater 

 rainfall is apt to be concentrated into torrential downpours, 

 and most of the water runs directly off the land into the streams. 

 The loch faithfully registers the increase and the changed 

 character of the rainfall. In April and May the level is falling. 

 Towards the end of May the loch is at bottom level. With the 

 entry of June it begins to rise more or less quickly, according 

 as the rainfall is above or below the average, and is, or is not, 

 torrential in character. The fall and subsequent rise of the 

 loch were well marked in May and June, 1912, the first half of 

 June being excessively wet. At the time of the first laying in 

 the beginning of May, 1912, the level of the loch was 0*6 metre 

 below the winter high-water mark. The level fell another 

 0"3 metre in the course of May. From June 10th to 17th the 

 water rose 0*7 metre. From this date the level of the loch fell 

 irregularly. Data were obtained for four pairs in as many 

 territories. In one instance the first laying was unknown. In 

 the other three instances both the first and second layings were 

 under observation. The first layings took place in the begin- 

 ning of May, and all came to grief from various causes. The 

 second layings occurred in the end of May and beginning of 

 June. The relation of the seven nests to the level of the water, 

 and the subsequent histories of the second layings, proved highly 

 interesting. The results are given in the form of a table which 

 is subjoined. The measurements are distances, no means being 

 available to measure the heights of the nests above water-level. 

 The fall of the loch was determined on two posts by the water- 



