Depriving homing pigeons of olfactory information by applying a local anaesthetic, gingicain, to their olfactory epithelium results in systemic effects. Furthermore, anosmia persists reliably for only an hour. In contrast, intra-nasal irrigation with 18 % zinc sulphate solution results in anosmia that persists for at least 5 days. No systemic effects of zinc sulphate on anosmic pigeons could be detected while monitoring their olfactory capabilities using the orienting response. To compare the orientation and homing of definitely anosmic, zinc-sulphatetreated pigeons with those of controls, I made releases from two different distances (9–24km, 63–70km). At shorter distances, pigeons treated with zinc sulphate showed no directional preference in their vanishing bearings, whereas both groups of control birds (sham-treated controls and untreated super controls) were well oriented. At the longer distances, the situation was more complex: pigeons treated with zinc sulphate were oriented but the chosen direction did not correspond with the home direction. The control groups did not show any directional preference. In all cases, fewer anosmic pigeons homed and they did so more slowly than did the controls

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