Data are presented on social and vocal learning in cowbirds (Molothrus ater) housed in large aviaries and given more degrees of freedom than in conventional experimental studies. The studies show that social and vocal outcomes are facultative responses to social contexts. Several findings are reviewed: First, cowbirds quickly self-organize into groups by age and sex; second, opportunities to interact across age and sex do exist and affect courtship competence; third, female cowbirds organize themselves differently in the presence and absence of male competition; and fourth, young, naive cowbirds show rapid and differential sensitivity to group dynamics. Taken as a whole, the data show that social Umwelten are dynamic, developmental ecologies.Solitude is a human presumption. Every quiet step is thunder to beetle life underfoot, a tug of impalpable thread on the web pulling the mate to mate and predator to prey, a beginning or an end. Every choice is a new beginning for the chosen.-Barbara Kingsolver, Prodigal SummerTerra firma provides humans with sure footing but sometimes narrow thinking about the sensory world of other inhabitants. The air-ground complex is one of myriad environments, many neither terra nor firma. Navigating and exploring underwater or underground as many animals do has also been intimidating for humans but is now yielding to newer technology and the continued persistence of those humans convinced of the value of knowing other worlds.Our goal here is to examine a broader contextual concept: How does a social world fit with a self-world? Is a social world merely the sum of self-worlds? Although most scientists agree that animals' sensory systems can be profitably analyzed by looking at animals one by one, scientists show less consensus that animals' perceptual systems, that is, how animals explore, respond, and categorize their sensory worlds, are uninfluenced by animals around them (Gibson, 1966). We propose that the social context matters even at basic levels of sensation and perception: Animals perceive compounded arrays of stimulation, and the salience of the Andrew P, King, Meredith J. West, and David J. White, Department of Psychology, Indiana University Bloomington.We thank the Howard Hughes Foundation, the Indiana University Department of Psychology, the Animal Behavior Program at the National Science Foundation, the Research Experience for Undergraduates Program at the National Science Foundation, and the National Science and Engi- parts depends on what else the animal is experiencing. To introduce our ideas means starting where Von Uexkull and other ethologists began, attempting to describe the compounded experiences animals may see, hear, smell, touch, taste, and feel (Von Uexkull, 1934/1957. But in this article, we address sensory pickup of social stimulation. A cross-modal dimension we stress is proximity, that is, being near to another animal. For example, the "sensation" dimension to which we refer is not seismic, as it might be for a rodent underground, but is the proximal "sens...