98 DAVID JENKINS AND ADAM WATSON 



the stock was healthy and had good breeding success, both parents stayed 

 with broods until these broke up in July or August and vigorous distraction 

 display by one or both sexes was the rule on the principal study area. It has 

 been rare there since. In 1957 adults and young behaved as discrete family 

 parties and stayed on their home territories. In 1958 and 1959 broods com- 

 monly disbanded and mixed; often there was only one adult with a brood 

 of chicks. Sometimes they moved to water and in August 1959 a number of 

 birds moved from the lower ground to hills where there were berries. 



STUDY AREA 



This paper is concerned with one study area of 1,135 acres (418 hectares) of 

 open moorland in Glen Esk, mostly at 200-270 m (700-900 ft) above sea- 

 level. It is apparently typical of many low grouse moors in north-east 

 Scotland and is surrounded by hills where we have other study areas. The 

 size of the area was decided arbitrarily so that it includes all the main physio- 

 graphical features of this particular locality. These are : two small farms with 

 some arable and inbye land; dry, peaty slopes; wet, rather boggy areas; 

 some moraine hillocks; streams; a wood; several gritty access tracks; and 

 patches of various types of moor vegetation [Molinia, Festuca and Deschampsia 

 grasslands; Juncus and Scirpus bogs; Ardostaphylos, Erica, Vaccinium slopes, 

 etc.). The heather is regularly burned with small fires of up to about 20 acres. 

 Nine tenths of the heather is less than 30 cm (twelve inches) high. 



Initially the area worked was 325 hectares (830 acres) of flat or gently 

 sloping moorland that was particularly suitable for counting grouse, but this 

 was extended to 418 hectares in December 1956 to include a hill rising to 

 about 360 m (1,200 ft). The purposes of the extension were to include some 

 hilly terrain different from the flattish remainder, to surround all the stubbles 

 where grouse are caught for marking, and to incorporate some large patches 

 of berried plants {Vaccinium myrtillus L. and V. vitis-idaea L.) in the study area. 



WEATHER 

 Summer weather does not seem to influence the fate of young grouse to any 

 great extent and brood sizes have been similar in wet and dry summers 

 (Jenkins, i960). As a rule winter snowfall does not worry grouse since it is 

 usually accompanied by wind that drifts patches of hill-top clear of snow, but 

 the winter weather may be important in other respects since it can have a 

 lasting effect on food supply. 



Prolonged low temperature and low humidity in the absence of snow have 

 been associated with widespread spoiling of heather which then goes brown 

 in colour. An apparently reasonable explanation is that the plants become 



