Food supply for settling male rock pipits affects territory size

Theory predicts that abundant food may favour larger breeding territories, provided that males could gain some important benefit, such as improved mating success or breeding performance, from keeping a large territory. The time saved when food is easy to find may be used to defend more space, unless increased defence costs offset the savings in foraging time. A previous experiment with concealed food addition close to laying did not reveal any effects on rock pipit, Anthus petrosus, territories. In this study the food intake rate of males was manipulated at the time of arrival from the winter quarters, by providing a concealed food source at the centre of each territory. The aim was to reduce foraging time, without attracting intruders, in order to isolate any effects of food abundance. Fed males had larger territories and tended to defend longer stretches of shoreline than control males. The difference in territory size was not related to male age or order of arrival. These results suggest that males settling at concentrated food sources may be able to establish large territories, and that keeping a large territory confers some advantage. We discuss possible reasons why food intake rate later during the breeding season did not affect territory size. (C) 1997 The Association for the Study of Animal Behaviour.