Young Fowler's toads from on and near the shores of a lake were tested in a circular pen 60 feet in diameter. Under a variety of conditions (e.g. including group tests, individual tests, simultaneous testing of two groups from different shores, long distance displacement, and transit to the test pen both in view of the sky and in lightproof containers), the toads oriented under the sun to a compass direction (Y-axis) corresponding to a line bisecting the home shoreline at right angles. This orientation persisted after 72 hours in darkness, indicating the existence of an internal clock mechanism. Reorientation to a new shore was evident in 24 hours and was virtually complete after 48 hours. Orientation failed or was partially inhibited in small toads tested under dense cloud cover, at noon, and after sunset. Also, the type of orientation exhibited under the sun was evident at night under the moon, but to a lesser extent under starry skies. These mechanisms are useful in foraging and in dispersal from nursery shores. Adults are oriented at night to the breeding site even without benefit of a chorus for reference. Adults oriented to the Y-axis of the breeding site. A recorded chorus distracted migrating adults pursuing a compass course toward a pond. Non-breeding adults compensated for a displacement made in view of the sun. Celestial orientation is considered a basic orientational mechanism which most likely developed early in anuran history.
