FLUCTUATIONS IN A RED GROUSE POPULATION 113 



to adjust the number of hens to the number of cocks and so regulate popula- 

 tion density. 



Sexual activity starts with the first mild weather in February or March. 

 The late winter periods of decrease have also occurred at this time and 

 perhaps they are associated with a second change in behaviour when both 

 sexes become more aggressive. The decrease may also be associated, as 

 perhaps in 1959, with a change in food supply or other resources. However 

 the process works, it is clear that the population levels observed are not due to 

 chance, nor primarily to mortality, but that numbers are regulated by some 

 active process operating through the behaviour of the grouse themselves. 



Perhaps the August populations have not been fully exploited by man, but 

 the amount of shooting depends chiefly on the enjoyment gained from a 

 certain expenditure of cash and energy. There is little consideration of 

 economics. In 1957 the study area grouse were probably exploited ideally 

 since the population was reduced to a level similar to that one might suppose 

 it would have fallen to anyway. Efficiency in exploiting a grouse population 

 must depend on knowing what the subsequent levels are likely to be. This 

 will depend on an accurate knowledge of the numbers of birds present and 

 their history and on local conditions. Whether the population is declining 

 or expanding may be important considerations and the condition of neigh- 

 bouring moors may be involved also. A great deal of further research is 

 necessary before the prediction of December population levels becomes a 

 likely possibility. 



ACKNOWLEDGEMENTS 

 Professor V. C. Wynne-Edwards has supervised and sponsored this work 

 and we are grateful to him for his advice and encouragement, and for the 

 faciUties available in his department at Aberdeen University. The field work 

 was done on the Glen Esk estate of the Earl of Dalhousie and we are greatly 

 indebted to him and to his factor. Major T. P. D. Murray. We have had 

 fruitful discussions with many colleagues and are particularly grateful to 

 Dennis Chitty and George Dunnet. 



SUMMARY 

 I. A long-term programme of research into the population dynamics of red 

 grouse is being organized in north-east Scotland. This paper is a prehminary 

 report on the methods used and the results obtained in the first three years. 

 The work described is an intensive study of the birds on 418 hectares (1,135 

 acres) of moorland at 210-270 m (700-900 ft) elevation in Glen Esk, Angus, 

 with particular reference to changes in numbers during autunm and winter. 



