Sibling competition selects nestlings to beg as quickly as possible when a stimulus in the nest entrance is presented. However, predation risk may select for nestlings to properly assess stimuli before begging, because nestlings that beg to erroneous stimuli may signal their position to a predator. The begging behavior of Coal Tit (Parus ater) and Great Tit (Parus major) nestlings to an artificial stimulus imitating a predator was examined. Sightless nestlings begged to the stimulus, but older nestlings did not. Developmental improvement of the sentient capacity, especially the acquisition of vision, might explain results of this study.