High‐speed displays encoding motor skill trigger elevated territorial aggression in downy woodpeckers. (30th November 2017) - Schuppe, Eric R.
Abstract: Many species perform social displays that incorporate complex body movements. However, the reason why such exaggerated behavioural signals evolve in the first place is unclear. Recent work posits that physical displays arise in part because they showcase an animal's motor skill—that is, the ability to produce challenging motor acts with great coordination, precision and/or speed. Support for this idea is largely correlational, with few studies attempting to manipulate metrics of motor skill to assess their effect on physical display efficacy. Here, we address this issue in the downy woodpecker ( Dryobates pubescens ). Individuals of this species compete for territories through the performance of drums, which are complex displays produced by rapidly hammering the bill against a resonate surface at rates of 16 hits/s. This display is a whole‐body endeavour, and its production relies on the ability to swiftly oscillate the head forward and backward at fraction‐of‐a‐second periods. Using a series of playback studies, we expose resident birds to experimentally engineered drums that reflect putative fine‐scale differences in the motor command of the head and neck. We show that resident individuals respond more aggressively to drums characterized by a cadence with a 9‐ms faster beat speed. These residents even modulate their own drum speed to resemble this high‐performance stimulus, although they often fail to reach it. Residents also appear to appraise drum acceleration by listening to the time intervals between successive beats in a single drum, while tracking how these time intervals change as the signal progresses. Our data support a connection between motor skill and the effectiveness of a physical display produced through elaborate body movement. We, therefore, suspect that motor skill is adaptive and evolves in response to selection by competition for effective drum displays. A plain language summary is available for this article. Abstract : Plain Language Summary