https://orcid.org/0000-0002-6254-2951
Abstract
Animals living in dense vegetation are limited in their use of visual signals due to the transmission constraints in these dim, cluttered environments. Birds in such habitats are often drab in appearance and thought to rely predominately on acoustic signals for conspecific communication. Here, we investigate the presence and use of a concealed underwing patch in the family Cettiidae. We find that this distinct white patch is widely present in the genus Horornis, with limited evidence for its presence in other genera. In response to simulated territorial intrusions, 2 species, Horornis fortipes (Brownish-flanked Bush Warbler) and Cettia castaneocoronata (Chestnut-headed Tesia) perform wing-flicking displays that results in a flashing effect in H. fortipes. The presence of white underwings raises interesting possibilities about the role of hidden achromatic patches in facilitating visual communication in habitats traditionally thought to be unprofitable for this modality.
RESUMEN
Los animales que viven en vegetación densa están limitados en el uso de señales visuales debido a las restricciones de transmisión en estos entornos oscuros y abarrotados. Las aves en estos hábitats suelen tener un aspecto poco vistoso y se piensa que dependen principalmente de señales acústicas para la comunicación entre individuos de la misma especie. En este estudio, investigamos la presencia y el uso de un parche oculto bajo el ala en la familia Cettiidae. Encontramos que este distintivo parche blanco está comúnmente presente en el género Horornis, con evidencia limitada de su presencia en otros géneros. En respuesta a intrusiones territoriales simuladas, dos especies, Horornis fortipes y Cettia castaneocoronata, llevan a cabo exhibiciones de aleteo que producen un efecto de destello en H. fortipes. La presencia de manchas blancas bajo las alas plantea posibilidades interesantes sobre el papel de los parches acromáticos ocultos en la facilitación de la comunicación visual en hábitats que tradicionalmente se consideraban desfavorables para esta modalidad.
Lay Summary
• Many birds living in habitats that are dark and cluttered are often “drab” in appearance, which can help them stay hidden from sight.
• How can species make themselves detectable in certain situations, such as when communicating with one another?
• We document the presence of hidden white patches under the wings of a group of drab, understory birds commonly called the bush warblers. Using museum specimens, citizen science photographs and written records in field guides, we investigate how widespread white underwing patches are across the family.
• We find that these patches are commonly found in species of Horornis warblers.
• Using high-speed video and experiments in the field, we show that birds might incorporate these patches during wing flick displays used in aggressive encounters.
• These hidden patches may be more frequently used than currently appreciated, and this observation invites further investigation into other “drab” groups of birds to understand their communication strategies.
