Most birds are characterized by a seasonal phenology closely adapted to local climatic conditions, even in tropical habitats where climatic seasonality is slight. In order to better understand the phenologies of resident tropical birds, and how phenology may differ among species at the same site, we used ~70,000 hours of audio recordings collected continuously for two years at four recording stations in Singapore and nine custom-made machine learning classifiers to determine the vocal phenology of a panel of nine resident bird species. We detected distinct seasonality in vocal activity in some species but not others. Native forest species sang seasonally. In contrast, species which have only had breeding populations in Singapore for the last few decades exhibited seemingly aseasonal or unpredictable song activity throughout the year. Urbanization and habitat modification over the last 200 years have altered the composition of species in Singapore, which appears to have influenced phenological dynamics in the avian community. It is unclear what is driving the differences in phenology between these two groups of species, but it may be due to either differences in seasonal availability of preferred foods, or newly established populations may require decades to adjust to the local phenology. Our results highlight the ways that anthropogenic habitat modification may disrupt phenological cycles in tropical regions in addition to altering the species community.

Morphological traits have served generations of biologists as a taxonomic indicator, and have been the main basis to delineate species for museum taxonomists for centuries. Widespread awareness of the importance of behavioural characters, such as vocalizations, has arisen much more recently, and the relative importance of these different traits in the speciation process remains poorly understood. To shed more light on the interplay between morphological and behavioral traits in the speciation process, we generated a draft genome of a cryptic Southeast Asian songbird, the Limestone Wren-babbler Napothera crispifrons, and re-sequenced whole genomes of multiple individuals of all three traditional subspecies and a distinct leucistic population that had previously been misinterpreted as a plumage polymorphism. We demonstrate strong genomic and mitochondrial divergence among all three taxa, pointing to the existence of three species-level lineages. Despite its great phenotypic distinctness, the leucistic population was characterized by shallow genomic differentiation from its neighbor, with only a few localized regions emerging as highly-diverged. Quantitative bioacoustic analysis across multiple traits revealed deep differences especially between the two taxa characterized by limited plumage differentiation. Our study demonstrates that speciation in these furtive songbirds is not governed by the evolution of marked color differences, but is regulated by an interplay between color and bioacoustic traits. Extreme color differences can be anchored in few genomic loci and may therefore arise and subside rapidly.