The function and evolution of vocal and visual signals in a Neotropical songbird, the Rufous-capped Warbler (Basileuterus rufifrons)

Animals communicate using multiple signaling modalities, with vocal and visual signals being the most prevalent in birds. The responses of animals to signal divergence among populations, along with the extent of divergence itself, may promote reproductive isolation and potentially speciation. Research on mating signal divergence, and experimental tests of responses to divergent signals, will expand our understanding of the mechanisms of reproductive isolation. In my dissertation, I investigated the form and function of vocal and visual signals in the Rufous-capped Warbler (Basileuterus rufifrons), a Neotropical resident songbird with complex song and bright plumage. I described male vocal behaviour in this species, and experimentally tested whether males and females showed seasonal variation in vocal behaviour during conspecific territorial interactions. I quantified range-wide variation in plumage, song, and morphology, and I experimentally tested whether two sympatric subspecies responded differently to each other’s songs. I found that male Rufous-capped Warblers have large, complex repertoires, and vary their singing behaviour depending on the season, time of day, and presence of conspecifics. I found that female Rufous-capped Warblers sing, which is the first report of female song in this species. Females used both songs and calls to contribute to joint territory defence, but they approached playback and sang most often in the non-breeding season. My results suggest that Rufous-capped Warblers comprise two distinct species, the northern, white-bellied B. rufifrons and southern, yellow-bellied B. delattrii, based on phenotypic differences between them and low responses to heterotypic signals by two divergent subspecies living in sympatry. My research provides insight into the vocal behaviour of tropical resident wood-warbler species, and adds to the growing number of studies showing that female signals function in territory defence in tropical songbirds. My findings also support a revision of the Rufous-capped Warbler’s taxonomic status, thus refining our understanding of biodiversity in wood-warblers and Neotropical animals

NEST DESCRIPTION AND NESTING BEHAVIOR OF THE RUFOUS-CAPPED WARBLER (BASILEUTERUS RUFIFRONS)

Abstract · The breeding biology of most tropical resident bird species is little-documented, particularly for sexually monomorphic species in which sex-specific contributions to nest-building and nestling provisioning are challenging to quantify. We describe nest structure and adult behavior throughout the nesting cycle for a color-banded population of Rufous-capped Warblers (Basileuterus rufifrons), a widespread sexually monomorphic tropical resident songbird. Using focal observations of 11 nests, combined with video monitoring during the incubation and nestling periods, we provide new information on this species’ nesting behavior, particularly sex-specific parental contributions to nest building, incubation, and nestling care. All nests were dome-shaped structures with a side entrance constructed of grasses, twigs, and leaves, as is typical for Basileuterus warblers. Females were the primary nest-builders, although we also observed male-assisted nest-building at one nest, which is a rare behavior in wood-warblers. Females were the sole incubators, and the incubation period in this population was 13–14 days. Video recordings confirmed that males and females made equivalent contributions to nestling feeding and nest sanitation. Our study provides detailed observations of both male and female Rufous-capped Warblers during all stages of the nesting cycle, and thus improves our understanding of nesting behavior in this common yet little-studied species.Resumen · Descripción del nido y comportamiento de anidación del Chipe gorrirrufo (Basileuterus rufifrons) La biología reproductiva de la mayoría de las aves residentes tropicales es poco conocida, particularmente para especies monocromáticas en que las contribuciones de cada sexo a la construcción de nido y la alimentación de los pichones son difíciles de observar. Describimos la estructura del nido y el comportamiento de los adultos durante todo el ciclo de anidación para una población anillada del Chipe gorrirrufo (Basileuterus rufifrons), una especie común de Paseriforme residente tropical monocromática. Con base en observaciones de 11 nidos y monitoreo de video durante los períodos de incubación y presencia de pichones, proveemos nueva información sobre el comportamiento de anidación de esta especie, particularmente sobre las contribuciones de cada sexo a la construcción de nido, la incubación, y el cuidado de los pichones. Todos los nidos presentaron estructura en forma de domo con entrada lateral, construidos con hierbas, palitos, y hojas, típicos de las especies de Basileuterus. Los nidos fueron construidos principalmente por las hembras, aunque en un nido observamos que la construcción fue asistida por el macho, un comportamiento raro en la familia Parulidae. Solo las hembras incubaron los huevos, y el período de incubación en esta población fue de 13–14 días. Los videos confirmaron que los machos y las hembras contribuyeron igualmente a la alimentación de los pichones y la limpieza del nido. Nuestro estudio provee observaciones detalladas de ambos sexos del Chipe gorrirrufo durante todo el ciclo de anidación, mejorando nuestro entendimiento sobre el comportamiento de anidación en esta especie común pero poco estudiada