Signals of aggressive intent are central in bird communication and my aim is to examine the use of vocal and visual displays during simulated and real territory intrusions in rock pipit males. Conspecific intruders are worth different energy investment because they constitute different threats. If owners are able to discriminate between various categories, they could act accordingly. I focused on calls as playback stimuli to judge their information content. I showed that various calls convey different signals to defending males. To identify vocal and visual displays elicited in real conflicts, I observed close encounters between neighbours in border zones and between owners and strangers within territories, respectively. A much discussed issue is whether aggressive displays predict approach, attack or even physical fight. My conclusion is that no single vocal component is a reliable signal leading to physical fights, but one particular, directed visual display is frequently seen before a clash and is then combined with intense vocalizations. The non-directed posture, with calls, is particularly common in the parallel walk display with neighbours. The vocalizations seem to express both aggressive intent, the directed calls, and low-frequency, defensive threat, the non-directed calls, while the males determine how to settle serious conflicts.
Bird communication, aggressive signals, vocal and visual displays, reliability, dear enemy, Anthus petrosus