The olfactory component of pigeon navigation: Steps of analysis

Abstract

179 experimental pigeons (EPs) made anosmic by bilateral olfactory nerve section, and 189 control pigeons (CPs), were released at distances of about 7.5, 30, 180, 500, and 700 km from their home loft. None of the birds had made any preceding homing flight. At short distances (7.5 and 30 km) both types of birds vanished from sight in a preferred compass direction (WNW) without regard to the direction of home. Homing speeds and return rates were lower in the EPs than in the CPs with the differences greater at 30 than at 7.5 km. At distances of 180 km, EPs were clearly inferior to CPs in homeward orientation, as can be read from initial orientation data, distributions of recoveries, and homing success. (Return rate was 35.5% in the CPs and zero in the EPs.) 500 and 700 km north of home, initial orientation revealed no homeward relation in both types of birds, but nevertheless some difference between CPs and EPs. Recoveries were clearly southward oriented in the CPs (which had been transported with their nostrils plugged), but not in the EPs. It is concluded that the range over which olfactory cues can be utilized for navigation can extend up to 500 km, 700 km, and more. For homing from very short distances, on the other hand, olfaction is not as indispensable as it is at longer distances. It is not yet clear whether, in a closer area around home, olfactory cues are supplemented or gradually replaced by other environmental cues. Even at longer distances (180 km) some weak homeward-pointing component persists in the EPs. It is unknown whether it is based on odour perception mediated by trigeminal nerves, or on additional, more or less redundant, sources of information, or whether the “map” component of pigeon homing requires both odorous and other stimuli. Average beeline distances covered from release to recovery site are positively correlated with the distance of displacement in the CPs, but not in the EPs. Some aspects of this finding are discussed. It is shown by one example that day-to-day fluctuations in initial orientation can apparently be caused by temporal fluctuations in olfactory conditions.