Anthropogenic noise, song, and territorial aggression in southern house wrens

Anthropogenic noise constrains the transmission of birdsong and alters the
behavior of receivers. Many birds adjust their acoustic signals to
minimize the interference of anthropogenic noise on signal transmission.
Birds may also change their acoustic signals to exchange information
during aggressive interactions. However, it is unclear how birds deal with
a potential trade-off between adjusting their acoustic signals to better
transmit in noisy environments versus mediating aggressive interactions.
Additionally, we do not know how urbanization and anthropogenic noise
alters the territorial behavior of receivers. We investigated the
interplay among song, territorial aggression, urbanization, and
anthropogenic noise, in males of the southern house wren (Troglodytes
aedon musculus), using recordings of spontaneous songs (non-aggressive
context) and a playback experiment simulating a male territorial intrusion
(aggressive context). We found that urban wrens behaved more aggressively
in response to the intruder by singing more and spent more time closer to
the intruder than rural wrens regardless of noise. Males produced songs
with lower minimum frequency and trills with wider frequency bandwidth and
higher vocal performance under acute (playback) than relaxed
(post-playback) aggressive encounters. These results suggest that males
use songs to communicate aggressive intent or fighting ability. Urban
wrens produced higher-pitched songs and trills than rural wrens
irrespective of aggressive context. Urban wrens in the noisiest
territories also produced the highest-pitched trills but only in the
non-aggressive context. Rural wrens in the noisiest territories tended to
produce the longest songs (non-aggressive context) or produced the
shortest songs (aggressive context). Results suggest that urbanization
affects territorial and vocal behaviors in southern house wrens. Males in
this species seem to primarily adjust acoustic signals in response to the
territorial intruder rather than noise.