Territory Size Variation in the Ovenbird: The Role of Habitat Structure

The hypothesis that structural habitat cues are the proximate factor determining territory size was tested by examining the relationships among habitat structure, prey abundance, and intrapopulation variation in territory size in Ovenbirds (Seiurus aurocapillus). Territory size was negatively correlated with prey abundance, with territory size decreasing as prey abundance per unit area increased. In addition, there was a significant difference in prey abundance per unit area between territory sites and areas of the study site not occupied by ovenbirds. A regression of prey abundance with variables describing the habitat structure of territory sites was significant, with habitat structure accounting for 73% of the variation in prey abundance among territories. This regression analysis, in combination with an additional discriminant function analysis of habitat occupancy, suggested a gradient of habitat quality as a function of vegetation structure that is related to both habitat selection and variation in territory size. To determine the possible mechanisms responsible for the inverse relationship between prey abundance and territory size, several hypotheses were considered. Both sampled prey abundance and predicted prey abundance as a function of habitat structure provided adequate models to explain the observed variation in territory size. Although an index of intraspecific competition was correlated with territory size, it was not significantly correlated with either sampled prey abundance or predicted prey abundance. Therefore, the index is not sufficient to account for the observed inverse relationship between prey abundance and territory size. A partial correlation analysis of territory size with prey abundance and predicted prey abundance supported the structural cues hypothesis, with variation in territory size being related to structural features of the habitat rather than prey abundance per se.