Behaviour 2019
Code of Silence? Crow Responses Vary with Changes in the Pattern of Pauses during Collective Cawing
Douglas W Wacker, Ileana M Rodriguez, Jared D Slattery, Andrea J Bilotta. University of Washington Bothell, Bothell, WA, United States

Research on cawing in American crows (Corvus brachyrhynchos) has often assessed the acoustic variation of isolated caw syllables emitted by individual crows.  However, crows often emit caw syllables in bursts (i.e., multisyllabic calls) and sometimes call collectively in groups.  For example, when crows mob predators, they collectively caw, with bouts of accelerated call emission and even overlap.  We aimed to determine whether patterns of caw call emission would alter assembly responses in crows.  We used recorded calls from an online repository, xeno-canto, to create three different playback files where pauses (i.e., the duration of silence between successive calls) were randomized, accelerated, or decelerated.  Decelerated playback led to significantly fewer movements towards the playback speaker and fewer crows within 30m of the speaker compared to randomized playback.  The closest approach of any crow to the speaker was also lower in response to randomized vs. decelerated playback.  Post hoc tests did not reveal differences in accelerated vs. randomized or decelerated playbacks.  These findings suggest that crows use collective cues when responding to group calling bouts.