Homing pigeons smell their way home, a new study confirmed.
They remember local smells to build up a mental map to guide themselves across many miles of unfamiliar territory back to their loft.
And experimental flights of pigeons confirmed artificial odours do not stimulate or trigger a pigeon’s navigation system.
Four decades ago it was proposed pigeons built up a mental map around their loft based on odours wafting in on the breeze.
Experiments showed homing pigeons without a sense of smell had dramatically reduced navigational abilities and this phenomenon was explained with the olfactory navigation hypothesis.
It predicts pigeons are able to build up an odour-based navigational map by associating the wind-borne environmental odours with the directions from which they blow at the home area.
When taken away from their loft, the pigeons are able to recognise the local prevalent odours characterising the release location, thereby determining the direction of home.
Once the birds know where they are relative to home, they can orient by using a sun or a magnetic compass.
But recently this hypothesis was challenged by the olfactory activation hypothesis.
This suggested pigeons can provide their way home provided they had been exposed to odourants during the outward journey, regardless whether these odourants were “map” odourants potentially learned in association with the wind directions, or novel artificial non-sense odourants.
In a series of experiments Professor Anna Gagliardo of the University of Pisa in Italy disproved this.
The study involved 63 adult inexperienced pigeons that were allowed to perform spontaneous flights in their home area.
They were then divided into three experimental groups then each fitted with a GPS-tracking device, and released singly 53 kilometres from home.
The first group was transported in open crates so they could smell their journey before being released.
The second group were carried and kept at the release site in airtight containers ventilated with natural air.
They were then were allowed to smell the environmental air at the release site for at least an hour before their sense of smell was temporarily switch off by having their nasal cavities washed with a zinc sulphate solution.
The third also travelled in an airtight container, with the air filtered to remove most of the natural odourants it might contain.
During the trip to the release site the birds were exposed to the artificial scents of lavender, eucalyptus, rose and thyme.
The third group were also given the nasal wash.
And the biologists found a noticeable difference between each group in terms of how well the pigeons could navigate.
As expected, most of the control pigeons found their way home successfully.
By contrast, the majority of the pigeons in each of the other two groups struggled to find their way home with an interesting difference between the two groups released under anosmic (smell disrupted) conditions.
The birds exposed to environmental odour cues performed significantly better than the birds stimulated with artificial smells.
Prof Gagliardo said: “Even the movements recorded on the first day of our test showed that only those birds exposed to natural environmental odourants were able to orient homewards.
“The birds that were stimulated with artificial nonsense odourants prior to their release were not able to orient in the home direction and flew significantly shorter paths on the day of release compared to the birds allowed to smell natural air both during transportation and at the release site.
“Our tests with GPS tracking experiments provided further evidence for the critical role the sense of smell plays in avian navigation,” she says.
The study was published in the Journal of Comparative Physiology A.
