Anosmia in ZnSO4-treated pigeons: loss of olfactory information during ontogeny and the role of site familiarity in homing experiments

Depriving homing pigeons of olfactory information by spraying an 18% zinc sulphate solution onto their olfactory ephithelium results in anosmia that persists for at least 5 days (tested using the ‘orienting response’). To study whether anosmic zinc-sulphate-treated pigeons (ZnSO4-pigeons) were able to compensate for their loss of olfactory information by using familiar landmarks, we made releases from two different distances (9–24km, 54–70km). The birds had homed once before from each release site. At shorter distances, ZnSO4-pigeons, sham-treated controls and untreated super controls were well oriented. At the longer distances, the anosmic pigeons and the sham-treated controls did not show any directional preference whereas the super controls were oriented towards home. In all cases, however, fewer anosmic pigeons homed successfully and their homing speed was slower than the speed of either control group. In order to determine whether experience during ontogeny affects the orientation behaviour, a group of young pigeons was reared anosmically by application of ZnSO4 solution once a week. A second group of experimental pigeons was made anosmic just before the critical release. When released at unfamiliar sites located between 15 and 24km from home, all but the group of short-term ZnSO4-pigeons were well oriented. Neither permanently nor temporarily anosmic ZnSO4-pigeons showed good homing performances. These data indicate that homing pigeons determine their home direction by relying on the navigational factors they have collected during rearing. The paradoxical finding that anosmically reared pigeons were oriented towards home but did not home successfully leads to the questions of whether intra-nasal irrigation with ZnSO4 solution results in extensive brain damage or whether initial orientation and the rest of the homing process are based on different mechanisms.