Our work on animal communication involves research that integrates behavioral and evolutionary ecology. We use a variety of methods and approaches including phylogenetic analysis, genomics, and field experiments of behavioral interactions to address the proximate and ultimate factors controlling variation in signals and signaling. We conduct the majority of our behavioral research on the white-crowned sparrow (Zonotrichia leucophrys), which is a well-studied model organism for studies on learning, communication and signal evolution. We also use comparative approaches to assess the tempo and mode of signal evolution in Neotropical suboscines (Aves: Tyranni).
URBAN DEPENDENT SELECTION ON BIRD SONG
Recording white-crowned sparrows holding territories in the Battery West section of the Presidio in San Francisco, CA.
Human activity has modified habitats and altered ecological and evolutionary processes around the world. Urban environments are some of the most highly modified habitats on the planet, as human density continues to increase in cities. Despite this, many species persist in urban settings. Most research has focused on the effects of urbanization on species diversity and conservation. Surprisingly, there has been comparatively little investigation into adaptations of species that remain in urban environments.
We are investigating the factors that influence the evolution of bird song in the urban environment. We have a unique opportunity to compare current and historical songs from urban and rural habitats for a subspecies of white-crowned sparrows (WCS, Zonotrichia leucophrys nuttalli) and will use this system to compare evolutionary trajectories of each location. Our previous research found an increase in low frequency urban noise in San Francisco, CA over a 30-year period. As predicted by signal detection theory, we found a concomitant increase in minimum frequency of WCS songs (Fig 1).
Building on these findings, our study will address three fundamental questions: (1) how are birds adjusting their song to the urban environment?; (2) how has song urbanization affected signal salience?; and (3) are urban songs adaptive? To address these questions, this study is using hand-rearing experiments, female choice tests, collection of behavioral and ecological data in the field, and development of the first mechanistic, individual-based model of quantitative song evolution, to investigate the mechanisms and consequences of song evolution in an urban environment. This work will transform our state of understanding of urban-dependent selection on mating behaviors and, more broadly, the adaptations of species that persist in urban environments. Results will inform both our understanding of how acoustic communication systems evolve as well as urban conservation efforts.
DIVERSIFICATION OF A PANTROPICAL RADIATION (AVES: TYRANNI)
Some of the diversity of bill shapes found in the Tyranni (images from Ridgely and Tudor 1994). Beginning at the species on top and moving clockwise, bill morphology and behavior of these furnariid species are convergent on that of nuthatches, jays, warblers, thrushes, tits and woodpeckers
The Passeriformes (“perching birds”) are divided into a cosmopolitan clade of ~4,500 songbirds known as the oscines (suborder Passeri) and a smaller, mostly Neotropical clade of 1,261 species known as the suboscines (suborder Tyranni). Although suboscines are relatively species-poor in the Paleotropics (only 59 suboscine species occur there) they constitute one of the predominant avian groups in many North American terrestrial habitats and in essentially all terrestrial habitats found in Central and South America.
The pantropical distribution of the Tyranni, and their prevalence throughout the Neotropical landscape make them a particularly well suited taxon to investigate diversification patterns and processes at intercontinental and continental scales. A first step in understanding the evolutionary pressures that have propelled this diversification is to characterize the patterns of diversification.
The unifying principle of this research is that a well-resolved molecular species-level phylogeny of the Tyranni will provide the conceptual foundation for a taxonomic revision of this suborder as well as a number of subsequent independent analyses of character evolution and biogeography.