Comparison of methyl anthranilate and denatonium benzoate as aversants for learning in chicks

Methyl anthranilate (MeA) has been widely used as a taste aversant for domestic chicks in the one-trial passive avoidance learning (PAL) task. However, MeA has a strong smell that may be aversive to chicks. Therefore, odourless denatonium benzoate (DB) has been suggested as an alternative taste aversant in PAL. The present study was designed to compare the efficacy of MeA and DB as aversants in the one-trial PAL task. In this task, young chicks peck a visually conspicuous bead coated with a taste aversant and in a single trial learn to avoid a similar, but uncoated bead at subsequent presentation. In Experiment 1, chicks were trained using a silver-coloured bead coated with 100% MeA, 0.5% DB or distilled water. After 3 h, MeA-trained, but not DB-trained chicks, exhibited significantly higher avoidance of the test bead than water-trained chicks. In Experiment 2, three pre-training presentations of an uncoated red bead preceded training with the silver bead. MeA-trained chicks showed significantly higher avoidance of the test bead than water-trained chicks. The numbers of water- and DB-trained chicks that avoided pecking the test bead were low and not significantly different from each other. However, DB-trained chicks exhibited significantly longer latencies to peck the test bead than water-trained chicks, indicating that they had retained some memory of the task. Thus, 0.5% DB is a weaker aversant than MeA and it does not induce high levels of learning in the one-trial PAL task. However, DB may prove useful for investigating weakly reinforced learning.