A study by German ornithologists has modelled how pigeons use
odours and winds to help them navigate their way home.
The navigation prowess of pigeons and other birds is not well
understood. What is known is that they need both a "map" (to know
where their home is) and a "compass" (to know which way north is).
Many researchers believe that the Sun and the Earth's magnetic
field are used to provide the compass part, but that doesn't
necessary help with the map part.
A paper published in Biogeosciences suggests that the map part is provided by
odours and winds in the atmosphere. There have been a number of
experiments over the last few decades that have shown that pigeons
struggle to find their way home when their sense of smell is
impaired or when they don't have access to natural winds at
Hans Wallraff from the Max
Planck Institute of Ornithology has collected air samples from
ninety different sites within a 300 kilometre radius around a
pigeon loft looking for particular volatile organic compounds --
the chemicals responsible for scents. The study revealed that the
ratios of these odours would increase or decrease in certain
directions. "For instance, the percentage of compound A in the sum
A+B or A+B+C+D increases the farther one moves from north to
south," Wallraff explains.
The changes in ratios of chemicals correspond with changes in
the perceived odour. However, if a pigeon has never left its loft
it will only know that odours change in certain directions if it
has been exposed to winds. So a pigeon sitting in its loft might
learn to associate an increase in the percentage of compound A with
southerly winds. So if it is then released 100 kilometres south of
home it may smell that there is more of compound A in the air and
know that it has to fly north to get back to the "home level" of
compound A. An analogy might be if a person could smell bagels from
their house whenever there was a wind coming from the south. If
they were then dropped somewhere where the smell of bagels was much
stronger, they might be safe to assume that they needed to go north
to find home.
Starting with this hypothesis, Wallraff built a model using real
atmospheric data in which virtual pigeons could only navigate using
knowledge of winds and odours they found at home. The model would
introduce random mutations to virtual pigeons, making them most
sensitive to those volatile compounds that are most effective for
navigation. Over the course of a thousand generations of pigeons,
the model could create virtual pigeons capable of finding their
bearings as well as real pigeons.
Wallraff believes that this is a "missing piece in the puzzle of
homing pigeon navigation" and shows that smells in the wind can
function as a map system.
"In this research, I wanted to find out whether and in what way
the chemical atmosphere fulfils the demands for avian navigation.
Eventually, to identify the chemical compounds birds actually use
for home-finding, we will need real birds again. But this is far in
This is not the first study to show the role that pigeons' sense
of smell plays in navigation. A 2011 study published in the Journal of Experimental Biology
showed that pigeons with a blocked right nostril were unable to
create the "map of smells" that guides them home.