Orientation and homing success of experienced and inexperienced anosmic pigeons

Abstract

Pigeons considerably experienced in homing (EX) and others completely inexperienced (IN) were released simultaneously at sites approximately 30 and 150 km from their home loft at Würzburg, Germany. Some of them had been made anosmic by means of bilateral olfactory nerve section (experimentais, EP); untreated birds served as controls (CP). EX/CPs were much better than IN/CPs in initial homeward orientation. Yet EX/EPs were not better than IN/EPs; their vanishing bearings were not homeward oriented at all. They showed, instead, a PCD (preferred compass direction) as is typical for birds from this loft. Over 150 km most of the EX/CPs (88%) but only 1 out of 39 EX/EPs returned to the loft (as against 24% and 0 of the IN birds). As shown by recoveries, the EX/EPs flew, on average, quite long distances but failed to orient their courses homeward. Recovery sites were, on average, farther from home than the release site. Over 30 km all the EX/CPs, but also almost half of the EX/EPs, returned to the loft (the latter, however, much slower than the controls). Return rates in the IN birds were 79 vs 16%. From the return rates over long and short distances it is concluded that goaloriented navigation over unfamiliar terrain requires an intact olfactory apparatus. Some redundancy of stimuli suitable for homeward orientation appears to exist at shorter distances. It is assumed that within a familiar area around home, which becomes larger with increasing homing experience, the pigeons are able to pilot to their loft by means of individually learned non-olfactory landmarks.