Effect of Body Size on the Resource Holding Potential of Male Varied Tits Parus varius.

Abstract

Resource holding potential (RHP) of males seriously affects their fitness in many species. We examined (1) whether RHP, such as priority access to food and success in obtaining a breeding place, differs among males and (2) if so, what factors affect RHP in male Varied Tits. Based on the observation of aggressive interactions at an artificial feeder in winter, we recognized a dominance rank linearity among fourteen males examined. Tarsus length affected priority for access to food. However, it is not known how priority for access to food affects a Varied Tit's survival in field. In the breeding season, eight of 14 males did not use nest boxes in the study area. Breeding males had a higher proportion of dominant interactions in winter than non-breeding males. Non-breeding males tended to have shorter tarsi than breeding males, although the difference was not significant. These facts suggest that male RHP has an important effect on their possibility of breeding. Reproductive success of breeding males did not correlate with tarsus length. This suggests that male body size did not affect the breeding performance once egg laying began.