Plumage polymorphism in raptors

ABSTRACT

Trait polymorphisms are a perennially popular topic of study in ecology and evolutionary biology. Plumage polymorphisms occur broadly in birds, with a particularly high rate among the raptors. The regularity of this heritable, melanin-based trait in raptors has prompted research into its potential connections to aspects of life history such as immune response, foraging ecology, and mating systems. Because raptors are a non-monophyletic grouping of multiple orders, they can further be leveraged to explore the eco-evolutionary drivers of recurrent plumage polymorphism phenotypes. Here we characterize plumage polymorphism throughout the raptors and review the existing literature on factors involved in its development and maintenance. We identify patterns and trends in this past body of research and discuss the opportunity to strengthen our understanding of plumage polymorphism through a holistic research approach. Specifically, we detail the likely benefits of applying genomic tools to plumage polymorphism research in raptors while encouraging both a focus on unstudied polymorphic species and on the potential interactions among multiple hypotheses that might promote plumage polymorphism.

RESUMEN

Los polimorfismos de rasgos son un tema de estudio popular que se mantiene vigente en ecología y biología evolutiva. Los polimorfismos del plumaje ocurren ampliamente en las aves, con una tasa particularmente alta entre las rapaces. La regularidad de este rasgo heredable en las rapaces, basado en la melanina, ha impulsado investigaciones sobre sus posibles conexiones con aspectos de la historia de vida como la respuesta inmune, la ecología de la alimentación y los sistemas de apareamiento. Debido a que las rapaces son un grupo no monofilético de múltiples órdenes, se pueden aprovechar aún más para explorar los factores eco-evolutivos que impulsan los fenotipos recurrentes de polimorfismo del plumaje. Aquí caracterizamos el polimorfismo del plumaje a través de las rapaces y revisamos la literatura existente sobre los factores involucrados en su desarrollo y mantenimiento. Identificamos patrones y tendencias en estas investigaciones pasadas y discutimos la oportunidad de fortalecer nuestra comprensión del polimorfismo del plumaje a través de un enfoque de investigación holístico. Específicamente, detallamos los probables beneficios de aplicar herramientas genómicas a la investigación del polimorfismo del plumaje en las rapaces, mientras alentamos tanto un enfoque en especies polimórficas no estudiadas como en las posibles interacciones entre múltiples hipótesis que podrían promover el polimorfismo del plumaje.

Lay Summary

• Plumage polymorphism, a trait where multiple color types occur within a bird population that are not explained by sex or age alone, is a common pattern throughout the raptors.

• The regularity of plumage polymorphism throughout the raptors has prompted much research on this group that has supported multiple explanatory hypotheses about polymorphism.

• Hypotheses to explain plumage polymorphism in the raptors are mostly related to their predatory ecology, and together suggest that for any one polymorphic species, multiple factors often interact to maintain plumage morphs.

• Previous research has provided many helpful insights but has focused on a small proportion of the world’s polymorphic raptor species. Most research is focused on the largest families, but in the most polymorphic of these—the owls—relatively few species have been studied.

• There is a broad opportunity to further develop our understanding of plumage polymorphism in the raptors through a variety of complementary research approaches undertaken in a holistic manner.