Song overlapping, noise and territorial aggression in great tits

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.