Response of domestic chicks to methyl anthranilate odour

Methyl anthranilate is widely used to make ingestive stimuli taste aversive in studies of visually mediated passive-avoidance learning in domestic chicks, Gallus gallus domesticusHowever, since methyl anthranilate smells strongly to the human nose, its odour may be involved in the learning process. We sought (1) to determine whether chicks can use the odour of methyl anthranilate as a disciminative stimulus in passive-avoidance learning and (2) to evaluate the use of denatonium benzoate as an alternative odourless reinforcer. In experiments 1 and 2, chicks were presented with familiar- or novel-coloured food or water, with or without the odour of methyl anthranilate or denatonium benzoate, to see whether either odour would elicit neophobia. Methyl anthranilate odour increased chicks' latency to eat or drink when it was presented in conjunction with novel-coloured food or water, showing that chicks can detect it. Denatonium benzoate had no effect. In experiment 3, chicks learned to avoid food or water that was made unpalatable by means of denatonium benzoate and paired with the odour of methyl anthranilate, showing that chicks can use this odour as a discriminative stimulus in taste-avoidance learning. In experiment 4, chicks learned to avoid pecking at a pin-head coated with denatonium benzoate or paired with the odour of methyl anthranilate, showing that denatonium benzoate is a satisfactory reinforcer for one-trial passive avoidance learning and that the odour of methyl anthranilate is in itself a punishing stimulus. We conclude that methyl anthranilate odour does influence avian learning and that denatonium benzoate is a suitable odourless alternative for use as a punishing stimulus.