Dissertation Research: Bird Song Divergence, Interspecific Territoriality, and Biogeography within a Sky Island Species Complex

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Territorial animals face challenges in recognizing and responding to the threat posed by competitors. Particularly interesting for studies of territoriality are circumstances where two closely related animals in strong competition for resources use dramatically different signals to deter intruders. Such a situation occurs at the narrow boundary between the recently diverged Moreau's and Fuelleborn's sunbirds, which differ dramatically in territorial song and appear to show highly disparate levels of territoriality towards one another. Intriguingly, the geographical distribution of these two species suggests that one is expanding its range at the expense of the other across the 'sky island' forest isolates of the Udzungwa Mountains, Tanzania. This study integrates experimental and molecular approaches to examine the causes and consequences of aggressive asymmetries between populations. To examine support for alternate hypotheses that explain apparent aggressive asymmetry, the study will employ a series of playback experiments in which territorial subjects incur a simulated intrusion via the broadcast of a competitor's songs. Using DNA sequence data, the study will examine: 1) whether one species has recently invaded the Udzungwa Mountains at the expense of the other, and 2) the extent of gene flow between species.This study takes advantage of an unusual 'sky island' contact zone between species to test how signal evolution and territoriality interact, and how such interactions may influence the long-term outcomes of competition among ecologically similar species. It is rarely possible to examine how behavioral differences might scale up to impact extinction-recolonization dynamics in island-like distributions.