High‐speed displays encoding motor skill trigger elevated territorial aggression in downy woodpeckers

Abstract

Abstract1. 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.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. 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.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-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. 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. K E Y W O R D Sdowny woodpecker, evolution, gestural signal, motor skill, territorial behaviourThis is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

Context-dependent scaling of kinematics and energetics during contests and feeding in mantis shrimp

“…A central and often exceptionally challenging goal of organismal biology is to measure animal performance in real behavioral contexts (Losos et al, 2002). Recent studies have used movementbased analyses to test how performance influences contest success (Briffa and Fortescue, 2017) or mate choice (Barske et al, 2011), or to ask how theories of sexual selection can be informed by performance measurements (Byers et al, 2010;Manica et al, 2017;Schuppe and Fuxjager, 2018). Our study contributes new evidence and approaches to reveal how the energy animals invest in powering movement can change with behavioral context.…”

Skeletal muscles that actuate sexual displays are specialized forde novoandrogen synthesis

“…Androgenic steroids can act via skeletal muscle to mediate many elaborate social displays that animals use for courtship and competition [29, 30, 33]. Our current study uncovers an important new dimension to this process by showing that select muscles that govern such behavior are likely specialized for de novo androgen synthesis.…”

“…The woodpecker LC is likely no exception, given that it is heavily enriched with androgen receptor [35]. Thus, local synthesis of androgens in this muscle probably supports its ability to generate a fast drum, which is more effective during territorial combat [33]. Precedent for this idea comes from experimental work in a species of tropical bird, called the golden-collared manakin ( Manacus vitellinus ).…”

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