VISUAL-SEARCH FOR CRYPTIC STIMULI IN PIGEONS - IMPLICATIONS FOR THE SEARCH IMAGE AND SEARCH RATE HYPOTHESES

In three experiments, detection of cryptic 'prey' was examined in pigeons, Columba livia, using an operant discrimination procedure and complex computer-generated stimuli. The first experiment manipulated the frequency with which each of two target types appeared within a session and found evidence for Tinbergen's claims that a high-frequency target is better detected than a low-frequency target. The second experiment suggested that an uninterrupted 'run' of encounters with one cryptic target facilitates performance and that this facilitation does not appear when two targets appear intermixed. This is consistent with previous findings, although the experiment indicated that improvements in detection occur only at a certain point during learning about the features of the stimuli. Experiment 3 confirmed this and showed that the improvement in detection following a run of encounters was temporary. Since the two targets were equally cryptic, these experiments refute the idea that improved detection results from a reduction in search rate, and provide evidence consistent with the search image hypothesis. (C) 1995 The Association for the Study of Animal Behaviour