Kinship and red grouse : the dynamics and behaviour of a declining population
Red grouse (Lagopus lagopus scoticus) undergo cycles of 4-10 year period and it has been proposed that cycling may be a consequence of intrinsic processes. The kinship hypothesis posits a positive feedback during the incline phase of a cycle between kin structure and recruitment of young males, and that this is overturned at high population density when competition among individuals is high. Negative feedback between population density and recruitment subsequently ensues, forcing the population into decline. Consistent with the predictions of such a model, high levels of kin structuring, and a positive relationship between kinship and recruitment have been shown in a natural population during the incline phase. This study uses a range of behavioural, molecular and statistical modelling techniques to examine aspects of the demography, dynamics and behaviour of grouse in the decline phase of a cycle. Specifically 1) patterns of recruitment through the decline phase 2) changes in kin structure through the decline phase and 3) the extent of aggressiveness with a reduction in population density. Observations revealed the percentage of new recruits that were young cocks reduced from 33% in 1999 to 22% in 2001 during the decline phase and were significantly lower than the 46-83% of recruits found to be young cocks during the incline phase. Kin structure was negligible through the decline phase, falling from 8 kin clusters the year after peak density in 1999 to no neighbouring first order relatives in 2002. Levels of individual aggressiveness, defined as call rate, fell between 1999 and 2000 and were found to be negatively influenced by kinship within years during the decline phase. Overall, such findings are in accordance with the predictions of the kinship hypothesis and therefore cannot refute that such intrinsic processes operate to drive cyclic dynamics in red grouse.