Fortune favours the aggressive: territory quality and behavioural syndromes in song sparrows, Melospiza melodia

While the relationship between aggression and resource value in competitions for discrete resources is well established, the relationship between aggression and territory quality is less well understood. Territoriality imposes spatial structure on social interactions: if spatial heterogeneity in habitat quality leads to clustering of high- and low-quality territories, and if consistently more aggressive individuals are more likely to obtain higher-quality territories, the resulting clusters of territory holders of similar aggression are likely to influence a wide array of social dynamics in territorial species, particularly when aggressive behaviour is consistently associated with variation in other behaviours, such as boldness. Using 8 years of historical nesting data in a northeastern population of song sparrows, we here determine (1) whether historical nesting success (defined both as clutch size and survival) is spatially clustered; and (2) whether aggression or boldness in first-year territorial males is correlated with the historical clutch size or nest survival of each maleʹs territory. We found significant clustering of both predation risk and large clutch sizes, even when controlling for the identities of historical territory owners. The aggressive behaviour of new territorial males was correlated with historical clutch size, but not with historical nest survival; in contrast, boldness was not correlated with either historical clutch size or nest survival. Thus, spatial variation in habitat quality is correlated with territorial aggression, but territory holders may either prioritize or be unable to assess all variables contributing to territory quality. In addition, a boldness-aggression syndrome does not necessarily result in both behaviours covarying with territory quality.