| Summary: | This study has been an attempt to gain a batter understanding of the factors involved in variation in aggressive behavior and clutch characters in the red grouse. Variation in physical clutch characters and chick behavior are described. Analysis of the relationships between these characters showed few overall correlations and thus did not indicate a small number of unitary causative factors behind the variation. Comparison of hens breeding in captivity showed that good chick survival resulted from a heavy hen parent. A study of breading over one generation demonstrated that egg weight, hatch weight and growth to 4 days showed varying degrees of maternal inheritance but no indication of genetic inheritance to any significant degree. Observations on groups of chicks from hatch to maturity showed no organized social structure based on aggressive behavior that might influences the dominance interactions of adults. The dominance remings of adult cocks were measured in small, temporary groups, and these rankings were stable for at least a year on retesting. Dominance was negatively correlated with late juvenile growth and positively correlated with comb size which is an indicator of testosterone activity. More dominant birds were also older, and moulted their primary feathers earlier. A model for the development of aggressive behavior is proposed in which external influences depress growth, thereby accelerating moult and increasing androgen production, which in turn determines adult dominance through aggression. This is discussed in relation to the model of population limitation by territorial behavior in the red grouse.
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