Only natural local odours allow homeward orientation in homing pigeons released at unfamiliar sites

Abstract

According to the olfactory navigation hypothesis, birds are able to exploit the spatial distribution of environmental odourants to determine the direction of displacement and navigate from non-familiar locations. The so-called "olfactory activation hypothesis" challenged the specific role of olfactory cues in navigation by suggesting that olfactory stimuli only activate a navigational system that is based on non-olfactory cues, predicting that even artificial odourants alone are sufficient to allow unimpaired navigation. In this experiment, we compared tracks of experimental birds exposed to different olfactory stimuli before being made anosmic at the release site prior to release. One group of pigeons was exposed to purified air enriched with artificial odourants, while a second group was exposed to environmental air. The birds stimulated with artificial nonsense odourants displayed several behavioural differences from both untreated controls and anosmic pigeons exposed to environmental air prior to release: nonsense odourants birds were unable to determine the home direction, they mostly flew within a space outside the homeward oriented quadrant, and they flew shorter distances on the day of release. Our data failed to support a mere activational role of olfactory stimuli in navigation, and are consistent with the olfactory navigation hypothesis.

Olfactory navigation versus olfactory activation: a controversy revisited

“…This was also the case when Anna Gagliardo, Enrica Pollonara, and Martin Wikelski submitted the paper that is published in the journal's current issue (Gagliardo et al 2018). In this study, the authors present findings that the authors interpret as inconsistent with the so-called olfactory-activation hypothesis.…”

“…Their claim was supported by experimental data obtained in Portugal (Jorge et al 2009(Jorge et al , 2010(Jorge et al , 2014. In the present issue of the Journal of Comparative Physiology A, Anna Gagliardo and colleagues report that they repeated one of the critical experiments and were not able to replicate these findings (Gagliardo et al 2011(Gagliardo et al , 2018.…”

“…Exactly this hypothesis is challenged by the current paper of Gagliardo and colleagues. Based on GPS tracking experiments, their study has failed to find support for the idea of a mere activational role of olfactory stimuli, but seems to be in agreement with the olfactory-navigation hypothesis (Gagliardo et al 2018).…”

“…However, the difference appears gradual rather than principal, as many of the initial bearings still lie in the home direction, and the number of late and lost birds were more similar than one would expect if natural odorants carried essential navigational information (Gagliardo et al 2018).…”

“…When released at a location in the opposite direction from home, both the control pigeons, which had been exposed to natural odorants at the false release site, and those exposed to nonsense odorants, oriented as if they had been released at the false release site. In the paper published in the current issue of the Journal of Comparative Physiology A, Anna Gagliardo and colleagues have tried to repeat this experiment using Italian pigeons and have shown that exposure to artificial odorants on the way to the release point has little or no effect on either initial orientation or homing (Gagliardo et al 2018).…”