Changes in the size of avian breeding territories in relation to the nesting cycle

Abstract

Changes in the territory size of birds in the course of their nesting cycle were examined, using data from field studies of the swallow, Hirundo rustica, and the yellowhammer, Emberiza citrinella, and from the literature for 37 other species. Swallows and yellowhammers had their largest territories in the fertile period of the female (nest-building and egg-laying periods) during both first and second clutches. Other species also mostly had their largest territories in the fertile period of the female with only a few species having a peak during pair formation or during the nestling period. Territory size peaked in the fertile period of the female irrespective of territory type (nest site, nest site with some food resources, or nest site with all food resources). Seven of these species had their largest territories in the fertile period of both the first and the second clutch. This pattern supports the hypothesis that prevention of extra-pair copulations is a major selective pressure causing males to maximize territory size and hence minimize the risk of intrusions and copulations by other males at the time when their female can be fertilized. Maintenance of a large territory is thus viewed as a mate-guarding behaviour.