Brightness Features of Visual Signaling Traits in Young and Adult Eurasian Eagle-Owls
Recent research has demonstrated the important role of visual communication in nocturnal birds. Achromatic plumage patches (i.e., pigment-free white feathers) with high levels of contrast against dark backgrounds are excellent candidates for visual signaling in the dark or at twilight, when differences in color may be less effective. In this study, with the goal of investigating the signaling role of certain achromatic plumage patches, we examined the characteristics and patterns of the brightness (i.e., total reflectance) of Eurasian Eagle-Owl (Bubo bubo) white feather patches for both young birds and adult individuals. Our results showed that (1) the total reflectance of young birds' white feathers differed significantly from that of adult owls' white feathers; (2) the brightness differed between the sexes in adults only, with females showing a significantly higher reflectance than males; (3) the total reflectance of the white patch around a young bird's mouth was positively correlated with brood size; (4) the total reflectance of the white badge on the throat of adults was positively correlated with their hematocrit values; (5) an assortative mating scenario based on the brightness of an individual's white badge was deemed possible; and (6) we did not detect any significant relationship in the levels of reflectance for related individuals: the young and their parents were not found to be distinguishable based on the brightness of their white feather patches. Trabajos recientes han demostrado la importancia del papel que las señales visuales desempeñan en la comunicación de las aves nocturnas. Los plumajes acromáticos (es decir, aquellos libres de pigmentos) con altos niveles de contraste contra un fondo oscuro son los mejores candidatos para enviar señales visuales en la noche o en horas crepusculares, cuando las diferencias de color pueden ser menos efectivas. Con el objetivo de investigar el papel en la señalización de ciertos parches de plumas acromáticas, estudiamos las características y los patrones de brillo (es decir, la reflectancia total) de la mancha blanca presente en polluelos y en adultos de Bubo bubo. Los resultados mostraron que (1) la reflectancia total de la mancha blanca de los polluelos difirió significativamente de la de los adultos; (2) en adultos existen diferencias en el brillo de la mancha blanca en función del sexo, siendo las hembras las que tienen valores más altos de reflectancia; (3) la reflectancia total de la mancha blanca de los polluelos está positivamente relacionada con el tamaño de nidada; (4) en el caso de los adultos, existe una relación entre la mancha blanca en la garganta y el valor de hematocrito de los individuos; (5) es posible que la mancha blanca de los búhos adultos actúe como una señal en un posible escenario de emparejamiento selectivo; y (6) no detectamos ninguna diferencia en el brillo de la mancha dentro de los núcleos familiares, es decir, los individuos de cada familia no parecen diferenciarse en función de los rasgos de la mancha blanca.Abstract
Resumen
The difference between the white patch around the mouth of a Eurasian Eagle-Owl young bird (A) and the white badge on the throat of a full-grown individual (B).
Sex-specific variation (males = stippled bar; females = open bar) in the total reflectance of white feather patches in Eurasian Eagle-Owl young birds and adult breeders.
Illustration of the significant relationship between the total reflectance of the white feather patch around young eagle-owls' mouths and brood size.
Illustration of the significant relationship between the total reflectance of the white feather badges on breeding Eurasian Eagle-Owls and their hematocrit values.
Variation in the total reflectance of the white feather badges within (males = stippled bar; females = open bar) and among breeding pairs of eagle-owls, illustrating greater variation among pairs than within pairs, thereby suggesting possible assortative mating based on feather brightness.
Contributor Notes
Associate Editor: Jeff P. Smith