Many birds communicate via a diverse set of vocalizations, but the contexts, roles, and structure of their varied songs and calls may change with age, differ between sexes, and vary temporally and geographically. In New World orioles, most tropical species exhibit the ancestral states of sexual monochromatism (both sexes have similar plumage) and monovocalism (both sexes sing and often duet together), whereas migratory temperate species tend toward dichromatism (males brightly colored and females drab) and divocalism (males sing almost exclusively). In this study, I examined the vocalizations of the Bahama Oriole, a non-migratory, monochromatic species, to learn where it fits within this generalized dichotomy; to document sources of variation in vocalization rates and spectrographic structure; and to improve survey design for this critically endangered species. Accordingly, this study describes the primary vocalizations of the Bahama Oriole, and examines how vocalizations vary with age, between sexes, at different times of day, during the breeding season, and among the three remaining island metapopulations on Andros, The Bahamas.
Hatchlings and fledglings produced vocalizations that were higher pitched than those of adults. Adults possessed a large repertoire, including five main vocalization types that were delivered independently or in combination. Second-year and after second-year-plumaged adults produced spectrographically similar vocalizations at similar rates. Although adult males and females could not be reliably distinguished in the field, both individuals of pairs were often heard giving the full range of vocalizations and frequently duetted together, particularly during the pre-incubation period. Antiphonal duets involved mated pairs, were limited to songs and whistle calls, and exhibited similar within-individual and between-individual variation in the spectrographic and temporal features of duets. Thus, the Bahama Oriole more closely resembles tropical oriole species (monovocal) than temperate species (divocal) in its vocalization behaviors. Adults vocalized at similar rates throughout the day prior to incubation, suggesting that surveys can be conducted at virtually any time of day during this period. Singing and most call types waned after chicks hatched, but whines increased dramatically as adults engaged in caring for their offspring. Minor but significant clinal variation in singing existed among the three metapopulations, suggesting possible cultural drift.
Lee, VA. March 2011. Vocalization behavior of the endangered Bahama Oriole (Icterus northropi): ontogenetic, sexual, temporal, duetting pair, and geographic variation. Master's thesis: Loma Linda University, Loma Linda, CA.