New Research Finds That Pigeons Navigate By Smell

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The ability of birds to navigate over incredibly long distances has fascinated people for hundreds of years. There is a body of evidence showing that an individual bird has the ability to migrate across hemispheres and return next spring to the very same tree where it was marked the previous year. John James Audubon conducted one of the earliest experiments in this area of research in 1803 when he tied a bit of thread to the leg of an Eastern Phoebe at his home in Pennsylvania before it migrated to some unknown location in the southern United States. He then observed the same bird on his property the following spring and like so many others wondered how a bird could achieve such a feat of navigation. Our current understanding suggests that birds navigate according to a variety of ways and means, including the position of the sun and stars, visual landmarks, bands of polarized light in the atmosphere, the magnetic fields of the Earth itself, and even chemical odors. It is thought that most birds probably use a combination of these cues and senses to find their way. Homing pigeons are probably the most recognized of avian navigators and are known to possess the incredible ability of somehow returning to their point of origin after being purposely displaced from a loft by as much as 800 km.

Generally speaking and with a few notable exceptions, such as vultures, birds do not have a very highly developed sense of smell and it has long been assumed that pigeons navigate by magnetic cues. However, creative experimental work published in 2001 by some Italian researchers discovered that pigeons rely on their sense of smell to detect volatile hydrocarbons for geographic orientation to at least some degree (Gagliardo et al. 2001). Recently completed research by Galiardo and colleagues, known as the Pisa experiments, has shown that pigeons rely on their sense of smell for navigation much more than was previously thought. This is exciting stuff because olfaction was always considered a secondary or even tertiary means of orientation in birds.

These researchers took 48 individual homing pigeons and surgically cut the nerves that relay information about smell to the brain in 24 birds and then severed what is known as the trigeminal nerve and is involved in the detection of magnetic fields in the other 24 birds. All of the birds were then transported 30 miles away from their loft and released. 23 of the birds that could no longer detect magnetic fields managed to find their way back to the loft within 24 hours, while only 4 of the birds that could no longer smell were able to navigate back to the loft and appeared to have lost all sense of direction with respect to their point of origin. These results suggest that smell is the key to how pigeons orient themselves and that they are actually able to perceive the landscape as some sort of odor map. This is an incredible discovery that forces us to reconsider what we thought we knew about avian navigation.


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