Agonistic behaviour of Mediterranean Peregrine Falcons during the breeding season: defending cliff territories from intruders

Agonistic interactions play a key role in structuring raptor communities, particularly in cliff-nesting assemblages where space and security are limiting resources. We investigated the frequency, intensity and temporal modulation of agonistic behaviour in a Mediterranean island population of the peregrine falcon Falco peregrinus, focusing on interactions with common ravens Corvus corax and other cliff-dwelling species. Using 15 years of standardised focal observations across 83 nesting cliffs, we quantified aggressive activities and actions and modelled their relationships with cliff characteristics, neighbour proximity, interacting species and breeding stage. Agonistic behaviour occurred at most cliffs, but in a minority of the sampling period (16%), indicating episodic but widespread territorial conflict. The intensity of aggression was primarily shaped by nearest-neighbour distance to other falcons, species-specific interaction asymmetries and breeding stage, rather than by cliff size alone or by social status (neighbour vs intruder). Peregrine falcons showed peak aggression during territorial displays and courtship, followed by a marked decline during incubation and chick rearing, whereas common ravens exhibited a progressive seasonal increase in aggression despite declining investment across breeding stages. These contrasting patterns indicate that seasonal aggression is not universally driven by increasing reproductive value of nest contents but instead reflects species-specific cost–benefit landscapes shaped by territorial rigidity, social structure and life-history strategy.