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WALTER NEUHAUS 



In another series of 222 trials with a tame robin redbreast {En'thacus 

 rubecula L.) using amyl acetate as a warning against NaCl polluted food 

 (meal worm or commercial bird food) no statistically significant scores 

 were obtained when all possibilities of optical orientation were avoided. 

 In the first 20 trials a score of 90 per cent was obtained, due to insufficient 

 avoidance of the possibility of optical discrimination. 



Table 1. Experiment on pigeons in a three-choice apparatus ; cdnditioning with 



BUTYRIC acid. 



In 1935 Zahn described an experiment in which a blue titmouse (Parus 

 caeruleus L.) after only 10 trials was able to discriminate against con- 

 taminated food scented with Skatole. In a series of 334 trials with the 

 same animal and the same odorous substance, we obtained a non-significant 

 score (54 ± 9 per cent), using the same experimental set up as with the 

 pigeons. Zahn reported that a thrush {Turdus meru/a L.) could be taught 

 to distinguish between clove oil in polluted food and rose oil scented food. 

 It was not possible for us to find an effective pollutive substance. Meal 

 worms which have been kept in concentrated sodium chloride solution, 

 tartaric acid or methanol were eaten without any hesitation. Instead, we 

 used a punishment in the form of an electric shock at the bowl of rose oil 

 while the bird obtained a reward in the form of a meal worm at the bowl 

 with dove oil. In 285 trials the score v/as in the random range. Using 

 optical marking instead of olfactory, 40 trials were enough to reach a high 

 score. In the last 20 trials a score of 95 per cent was obtained. 



Finally a series of experiments with geese in an apparatus similar to the 

 one Michelsen (1959) used in his experiments with pigeons will be described. 

 It was designed to teach the pigeons to correlate smell or lack of smell with 

 colour signs. After a correct choice of a colour associated with the pre- 

 sence or absence of the odour of butyric acid, they were rewarded with 

 food. The scores obtained in 691 trials with a male and 729 with a female 

 goose were in the random range, while Michelsen's pigeons were able to 

 correlate smeJJ and colour correctly. 



All those negative experiments of ours show that it is very difficult indeed 



