Data from: High-speed displays encoding motor skill trigger elevated territorial aggression in downy woodpeckers

1) Many species perform social displays that incorporate complex body movements. However, the reason why such exaggerated behavioral signals evolve in the first place is unclear. 2) 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. 3) 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 sec-1. This display is a whole-body endeavor, and its production relies on the ability to swiftly oscillate the head forward and backward at fraction-of-a-second periods. 4) 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-msec 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. 5) 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.

1) 诸多物种都会展现包含复杂肢体动作的社交展示行为，但这类夸张的行为信号最初为何会演化而来，目前尚无定论。
2) 近期研究提出，物理展示行为的出现部分源于其能够展现动物的运动技能（motor skill）——即通过出色的协调性、精准性和/或速度完成高难度动作的能力。目前该假说的支撑证据多为相关性数据，鲜有研究通过操控运动技能的相关指标，来评估其对物理展示行为效能的影响。
3) 本研究以绒啄木鸟（*Dryobates pubescens*）为研究对象，探讨这一科学问题。该物种通过鸣鼓行为争夺领地，这类复杂展示行为是指以每秒16次的频率，快速用喙敲击共振面所产生的声响。鸣鼓属于全身性的动作，其完成依赖于在极短时间内快速往复摆动头部的能力。
4) 本研究通过一系列回放实验，向领地内的留居个体播放实验设计制作的鸣鼓声响，这些声响反映了头部与颈部运动指令的潜在细微差异。实验结果显示，留居个体对节奏快9毫秒的鸣鼓声响会展现出更强烈的攻击性反应。这些留居个体甚至会调整自身的鸣鼓速度，以匹配该高性能刺激信号，但往往无法达到该速度水平。此外，留居个体似乎会通过聆听单次鸣鼓中连续敲击的时间间隔，并追踪这些间隔随信号推进的变化，来评估鸣鼓的加速度特征。
5) 本研究的数据证实了运动技能与复杂肢体动作所产生的物理展示行为的效能之间存在关联。因此我们推测，运动技能具有适应性，且会因针对高效鸣鼓展示的竞争选择压力而演化。