The structure of dominance hierarchies in the Paridae : consequences for foraging efficiency and body condition
In species that form social foraging groups during all or part of their lifecycle, individuals are subject to costs in terms of a higher frequency of aggressive interactions and having to share resources with group members, which must be outweighed by the benefits of flocking for all individuals concerned if it is to remain an Evolutionary Stable Strategy. In many group living species, dominance hierarchies exist that reduce the need for repeated agonistic interactions between the same individuals, which use valuable energy and may result in injury. Dominance hierarchies allow the most dominant individuals priority of access to contested resources whilst subdominant individuals may suffer as a consequence. In this thesis, I examined how dominance hierarchies were structured in great tits, blue tits and coal tits and how dominance status affected an individual's foraging efficiency and body condition. The food handling times or vigilance levels of great tits and blue tits were not governed by dominance status but dominant coal tits were less vigilant than subdominant conspecifics thus probably allowing more time for foraging and other social activities i.e. mate finding and territory defence. Though subdominant great tits did not suffer costs in terms of food handling times, they were affected more by interference competition when foraging in mixed tit flocks compared to dominant great tits. Using ptilochronology as a measure of nutritional condition, the results from coal tits in this study contradicted those of previous studies in that dominant coal tits had slower rates of feather growth and produced feathers that were shorter and less dense than subdominant conspecifics, possibly a cost of their high dominance. Feather growth rate in great tits and blue tits was not related to dominance status. The immunocompetence of adult great tits or blue tits was not governed by dominance status nor did great tit or blue tit nestlings show any relationship between their place in the brood competitive hierarchy and immuocompetence.