| The steroid hormone testosterone influences the behavior of male birds in diverse ways. Since 1972, a significant body of research has focused on testosterone's influence on the foraging behavior of the domestic chicken (Gallus gallus domesticus); guiding the majority of this research has been R. J. Andrew's hypothesis that testosterone primarily affects foraging by ‘stabilizing’ males' attention to an entrained task. The evidence supporting Andrew's hypothesis is also consistent with two alternative hypotheses: testosterone may induce a change in the focal distance of the chicken eye, or it may influence chickens' processing of spatial information and object-specific appearance cues that are critical in the learning and performance of foraging tasks. I tested Andrew's stabilization of attention hypothesis, and also evaluated the two alternative hypotheses, in a series of four experiments. I measured the effects of testosterone on chicks' responses to a novel food stimulus, in an experiment designed to isolate stabilization of attention from visual and spatial processing. I examined chicks' feeding patterns in an open-field foraging experiment, and also studied their behavior as they fed from moving food sources, in tests of the stabilization of attention and increased lateral focal distance hypotheses. Finally, I tested chicks in an arena where both spatial and object-specific cues could be associated with food, and then evaluated the effects of testosterone on cue selection. In all four experiments, the data showed no significant pattern of differences in the foraging behavior of testosterone-treated and control chicks. I concluded that the effects of testosterone on foraging behavior in the domestic chick are much less robust than suggested by the literature and, if present, are likely to depend on such things as the breed and age of the animals. |
