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Experiments have shed much light on the begging behaviors of baby songbirds. A. Songbird species that are especially vulnerable to predators have evolved ways of reducing the dangers associated with begging calls. B. Songbird parents focus their feeding effort on the nestlings that beg loudest for food. C. It is genetically disadvantageous for nestlings to behave as if they are really hungry when they are not really hungry. D. The begging calls of songbird nestlings provide a good example of overly damaging cost to signalers of signaling. E. The success with which songbird nestlings communicate their hunger to their parents is dependent on the frequencies of the nestlings' begging calls. F. Songbird nestlings have evolved several different ways to communicate the intensity of their hunger to their parents.