Newly hatched Mallard ducklings Anas platyrhynchos freeze when they hear the maternal alarm call, which the hen utters when there are potential predators near the nest. Previous laboratory experiments have shown that this freezing response decreases with age; specifically, 72 hold ducklings exhibit significantly less freezing than ducklings 12 or 24 h old. The present study was conducted to assess whether this decline in freezing is the result of greater arousal brought about by having been reared without food or water for three days–rearing conditions often used in experiments on young ducklings and that mimic natural conditions. Thirty ducklings were reared with food and water, and another 30 were reared without food or water. At 72 h of age, the ducklings that had been fed and watered weighed significantly more than the deprived ducklings. Against predictions, they were significantly more vocal than deprived ducklings. Most importantly, both groups exhibited comparably low levels of freezing. Thus, as we had previously concluded, the decline of freezing in ducklings at 72 h is probably an ontogenetic adaptation associated with leaving the nest. Moreover, although freezing declines by 72 h, the physiological response to the alarm call (heart rate) persists for at least 1 week. Thus, there appears to be a decoupling of the behavioral and physiological responses to the alarm call.
Bird Behavior is an international and interdisciplinary journal that publishes high-quality, original research on descriptive and experimental analyses of species-typical avian behavior, including the areas of ethology, behavioral ecology, comparative psychology, and behavioral neuroscience.