Variation in the function of Eagle Owl vocal behaviour: territorial defence and intra-pair communication?

The main aim of this work was to investigate the possibility that in territorial males of a species present throughout the year on their territory with their mate, there are manifest differences in the call functions within the call period. I listened monthly to dusk call displays of 17 Eagle Owl Bubo bubo males from early October to mid-February. Two different call periods exist in this species: in the first (October-December), the territorial function seems to be predominant, whereas in the second (January-February), calling related to mating prevails. Actually, in this latter period the behaviour of both male and female changes: both mate duets and number of copulations after them increase, and the choice of song posts and male vocal behaviour are different. The call functions are discussed in terms of the male-announcement, female-reproduction and territoryestablishment hypotheses.