Pigeon homing: site simulation experiments with bird-borne direction recorders.

Previous experiments showed that pigeons allowed to smell olfactory cues at a 'false' release site, and subsequently transported to and released from another unfamiliar locality, oriented according to the home direction at the false site but eventually homed despite their wrong initial orientation. In the above 'site simulation' experiments, data collection was restricted to the initial bearings and homing performance, and no information was obtained on the actual route flown by pigeons. Route correction in site simulation tests is now investigated by releasing pigeons equipped with bird-borne direction recorders to track their route. Our results show that the experimental birds can actually fly for a long time in wrong directions, related to the home direction at the false release site, before correcting their path to the true homeward direction. This correction occurs 2 h or more after release, when the birds are supposed to have recovered from the anaesthesia of their olfactory membranes which they had been subjected to just prior to release. This result confirms the basic role of the olfactory information, collected during the outward journey, in the pigeon's homing process.

Orientation of pigeons exposed to constant light and released from familiar sites.

It has been proposed that homing pigeons may use pilotage to orient home when released from familiar sites. To test this possibility, a group of pigeons was released from familiar locations after being exposed to a constant bright light. This treatment produced the loss of the circadian rhythmicity of general activity of the birds and thus presumably impaired their time-compensating sun compass mechanism. Experimental birds, both anosmic and olfactorily unimpaired, did not show any tendency to orient home, their bearing distributions being generally not different from random. Their homing performances were also affected. These results show that initial orientation of pigeons released from familiar sites entails the use of the sun compass even when the birds are released after a treatment that makes them arrhythmic in their activity. The possibility that pilotage may play a role in the first part of the homing flight of pigeons remains to be demonstrated.