Song overlapping, noise and territorial aggression in great tits

Abstract

Communication often happens in noisy environments where interference from the ambient noise and other signallers may reduce the effectiveness of signals which may lead to more conflict between interacting individuals. Signallers may also evolve behaviours to interfere with signals of opponents, e.g. by temporally overlapping them with their own, such as the song overlapping behaviour that is seen in some songbirds during aggressive interactions. Song overlapping has been proposed to be a signal of aggressive intent, but few studies directly examined the association between song overlapping and aggressive behaviours of the sender. In the present paper we examined whether song overlapping and ambient noise are associated positively with aggressive behaviours. We carried out simulated territorial intrusions in a population of great tits (Parus major) living in an urban-rural gradient to assess signalling and aggressive behaviours. Song overlapping was associated negatively with aggressive behaviours males displayed against a simulated intruder. This result contradicts the hypothesis that song overlapping is an aggressive signal in this species. Ambient noise levels on the other hand were associated positively with aggressive behaviours but did not correlate with song rate, song duration or song overlapping. Great tits in noisy urban habitats may display higher levels of aggressive behaviours due to either interference of noise in aggressive communication or another indirect effect of noise.