Characteristics and level of aggression by female Pied Flycatchers at different distances from the nest hole

Abstract

Proposed reasons for female aggression include defence of nest site or food resources on their territory, prevention of intraspecific brood parasitism or infanticide, or monopolisation of male's contribution to feeding of young. Here I investigate the characteristics and the level ofaggression of Pied Flycatcher (Ficedula hypoleuca) females at different distances from the current nest site during the nest building and egg laying period . A live female was presented in a cage 1, 10, 20 and 40 m away from the nest box of the females and the behaviour of the focal females was recorded. In total, we conducted 76 presentations (19 per distance category). The time spent by females at their own nest box increased significantly with the decreasing distance of the intruded female . This suggests that females used staying at their own nest box as a defence when an intruder was very close. Female aggressive behaviour was concentrated around the nest site and decreased gradually as the distance from the nest hole increased. The main reason for female aggression seems to be the need to defend their own nest site against intruders. However, this does not totally exclude the importance of other reasons for female aggression . Both the intensity and characteristics of female-female aggression were dependent on the distance from the current nest site . This should be taken account when different studies on the level of female aggression are compared.