Suppression of Autumnal Migratory Unrest in Dark-Eyed Juncos Held During Summer on, Near, or Far From their Previous Wintering Sites

Abstract

Abstract In previous experiments, Dark-eyed Juncos (Junco hyemalis) were captured on a winter home range to which they had shown year-to-year site fidelity and held there until just before the autumn. They failed to show normal autumn migratory restlessness and fattening, which suggested that previous experience at the migratory destination suppressed readiness to migrate. We asked what the suppressing cues might be. Possibilities included very local features peculiar to the individual's winter home range (e.g. its trees) and cues common to the general region (e.g. geophysical or celestial information); features of the latter sort might give information about latitude. To test these possibilities we monitored autumn restlessness and fattening of new groups of juncos that were held before migration where some could perceive landmarks of their familiar winter home range and others only more general information about their location. In autumn those held at, near, and far south of their winter home ranges again failed to become restless or fat. A small group held far north of their winter home ranges became somewhat restless, significantly more so than the others. These may have perceived that they had not reached their usual winter latitude, but alternative explanations are possible.