Male black-capped chickadees begin dawn chorusing earlier in response to simulated territorial insertions

Variation in the level of competition for mates and territories is likely to influence the behaviour of competitors. The start of the dawn chorus in songbirds is influenced by a variety of internal factors (e.g. circadian rhythms) and external factors (e.g. light levels, social cues). Here we investigate whether the start time of the dawn chorus is influenced by the singing behaviour of conspecific competitors. Using an Acoustic Location System, we recorded the dawn chorus in neighbourhoods of 5–10 black-capped chickadees, Poecile atricapillus. We used playback to simulate an unfamiliar male performing a dawn song bout within an existing male’s territory. Playback began 15 min before the earliest song sung by any male on the preceding day. Focal males began singing a mean ± SE of 4.3 ± 1.6 min earlier on the day of playback (time relative to sunrise), significantly earlier than on the previous day. We also found a significant communication network level response where neighbouring males began singing 2.3 ± 0.8 min earlier in response to playback. Dawn song bouts of males that received playback were longer, but ended at a similar point relative to sunrise. As this effect of a simulated conspecific on chorus start time is on the scale of only a few minutes, other factors probably play a significant role in shaping the timing of dawn chorus onset. Our results show that animals adjust the timing of their sexual communication in response to increased levels of competition.