I assumed that birds use the geomagnetic field to fly halfway around the world. They don’t. Not all of them.
Homing pigeons, it turns out, use smell. At least for a few hundred miles. Although, at shorter distances:
within a familiar area, pigeons navigate by relying on landscape features memorised during their previous homing flights.
Beyond that… Forty years of olfactory navigation in birds (2013): Forty years ago, Papi and colleagues discovered that anosmic pigeons cannot find their way home when released at unfamiliar locations.
The paper covers clever experiments that factor out magnetic and other mechanisms, and there’s evidence for the olfactory hypothesis:
Pigeons housed in aviaries provided with clockwise or counter-clockwise deflectors, once released, displayed a corresponding deflection in initial orientation.
Homing pigeons do particularly well in the Mediterranean characterised by an environment richer in natural odours than elsewhere due to its high biodiversity of plant species.
Utterly fascinating to imagine what that smell-map is like:
the odour-based map does not have the structure of a map defined by a bicoordinate system, thereby giving the exact position and distance of two points with respect to each other. The olfactory map is supposed to provide information exclusively about the direction of displacement.
So homing pigeons don’t what3words themselves to a specific point but rather hot-and-cold themselves towards home.
They also memorise the smell-trajectory on the way out:
odours perceived during transportation indeed constituted a source of positional information
(Although it’s not essential.)
stable ratios, rather than the absolute concentrations, of at least three different volatile compounds are sufficient
It takes a while to learn. Homing pigeon navigational ontogeny (2024): Learning of an olfactory map occurs during the first months after fledging, when pigeons memorize the odours carried by winds blowing at their home loft in association with the wind’s direction.
These are very dry statements. So there’s also Odors as navigational cues for pigeons (2020) talking about work in Tuscany:
Some of these compounds are emitted by trees, the pine fragrance one smells during a walk in the forest. Other pungent natural emissions come from the sea, while still further VOCs can be emitted from industry.
And what an insight into the world of a homing pigeon!
Beyond the smell-map range? Beyond ~200km, at a continental scale?
Homing pigeons listen to infrasound.
Infrasound detection by the homing pigeon: A behavioral audiogram (1979):
Homing pigeons could detect extremely low frequency sounds (infrasounds) as low as 0.05 Hz in a sound isolation chamber. …
Natural infrasounds come from many sources including weather patterns, topographic features, and ocean wave activity. Infrasounds propagate long distances and can be detected hundreds or even thousands of km away from their sources.
That is to say: thunderstorms, magnetic storms, earthquakes, jet streams, mountain ranges, and rocket launchings
are all global landmarks for these birds.
Homing pigeons listen to the song of mountains and the ocean swell.
What a picture of our planet they have.
Caveat: the evidence for infrasound use is less strong than the olfactory map. The capability is there and there’s circumstantial evidence via Concorde but no direct tests that I can find.
Although homing pigeons don’t rely on it, other birds do indeed use the geomagnetic field.
It’s in their eyes.
How evolution has optimized the magnetic sensor in birds (2024):
magnetoreception is based on a complex quantum mechanical process that takes place in certain cells in the retinas of migratory birds.
It’s migratory birds specifically: cryptochrome 4 is more sensitive in robins than in chickens and pigeons.
Imagine being able to see an extra colour and that colour is north.
I went through a period attempting to imagine my way into the umwelt of a dog, how dogs perceive the universe (2004): You don’t smell a lion, you smell 70% of the likelihood of a lion – is it nearby in space, or in time?
There is no cognition step between sense and act with smell.
Smell is all about moving through the insides, through a field of intensities, of potential.
Whereas the world of vision, of surfaces, gives us room to think before acting.
Learning about homing pigeons takes me right back to those thoughts.
I assumed that birds use the geomagnetic field to fly halfway around the world. They don’t. Not all of them.
Homing pigeons, it turns out, use smell. At least for a few hundred miles. Although, at shorter distances:
Beyond that… Forty years of olfactory navigation in birds (2013):
The paper covers clever experiments that factor out magnetic and other mechanisms, and there’s evidence for the olfactory hypothesis:
Homing pigeons do particularly well in the Mediterranean
Utterly fascinating to imagine what that smell-map is like:
So homing pigeons don’t what3words themselves to a specific point but rather hot-and-cold themselves towards home.
They also memorise the smell-trajectory on the way out:
(Although it’s not essential.)
It takes a while to learn. Homing pigeon navigational ontogeny (2024):
These are very dry statements. So there’s also Odors as navigational cues for pigeons (2020) talking about work in Tuscany:
And what an insight into the world of a homing pigeon!
Beyond the smell-map range? Beyond ~200km, at a continental scale?
Homing pigeons listen to infrasound.
Infrasound detection by the homing pigeon: A behavioral audiogram (1979):
That is to say: are all global landmarks for these birds.
Homing pigeons listen to the song of mountains and the ocean swell.
What a picture of our planet they have.
Caveat: the evidence for infrasound use is less strong than the olfactory map. The capability is there and there’s circumstantial evidence via Concorde but no direct tests that I can find.
Although homing pigeons don’t rely on it, other birds do indeed use the geomagnetic field.
It’s in their eyes.
How evolution has optimized the magnetic sensor in birds (2024):
It’s migratory birds specifically:
Imagine being able to see an extra colour and that colour is north.
I went through a period attempting to imagine my way into the umwelt of a dog, how dogs perceive the universe (2004):
Whereas the world of vision, of surfaces, gives us room to think before acting.
Learning about homing pigeons takes me right back to those thoughts.