Factors affecting recruitment in Red Grouse
Red grouse (Lagopus lagopus scoticus Lath.) populations often show cycles in numbers. It has been suggested that these are caused by positive feedback between population kin structure and recruitment of young cocks to the territorial population, and by negative feedback between population density and recruitment. In previous studies of red grouse in north-east Scotland, recruitment was the key demographic factor affecting population change. Changes in recruitment were the result of changes in breeding success and changes in the proportion of young cocks establishing territories in autumn. This thesis investigates the differences between those young males which successfully established a territory and those that did not, on a heather moorland on the edge of the Cairngorm mountains, north-east Scotland. It describes the behaviour and movements of young cocks during the period of territory establishment. In particular it is shown that young cocks which had more close relatives as neighbours were more likely to establish a territory. However, investigation of the effect of relatedness on the aggressive interactions between cocks did not reveal any robust behavioural mechanism by which this relationship might have come about. Relatedness between individuals was estimated from microsatellite genetic data. Young cocks which established territories had larger supra-orbital combs than those which did not. This suggests that hormonal status is important in determining recruitment success, since comb size is an indicator of the level of circulating androgens of an individual. Territory establishment by young cocks took place rapidly in mid-September following the break up of broods. Young cocks were never observed to win encounters with old established cocks during territory establishment. Persistence in engaging in encounters may be more important than winning them.