In altricial birds, nestlings usually respond to the sound and appearance of the provisioning adults by begging for food when the adults arrive at the nest. Nestlings can, however, also beg incorrectly on hearing misleading sounds in the environment and fail to beg when the adult arrives. This study uses the blue tit Cyanistes caeruleus to test the hypotheses that nestling begging strategies are influenced by the reliability of the stimulus to beg, and that nestling motivational state affects the response to different stimuli. Here, we show experimentally that nestling hunger strongly influences the response to stimuli that vary in their reliability. While hunger increases begging rate, it also increases the likelihood that nestlings will beg when the parent is absent. This is in agreement with both the predictions of signal detection theory and recent empirical work on other species. We found, however, no evidence that age-related perceptual constraints influence the begging response of ten day old nestlings to different stimuli.