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Homing pigeons go by smell, study suggests

Nov. 11, 2013
Courtesy of the European Geosciences Union
and World Science staff

Smell may ac­count for the ex­tra­or­di­nary navig­ati­onal skills of hom­ing pi­geons, a study says.

Hom­ing pi­geons are do­mes­ti­cat­ed pi­geons bred for their abil­ity to find their way to their home lofts when moved away long dis­tances—in some cases, as much as one-seventh the width of the Earth. How they man­age to find their way back is still de­bat­ed, es­pe­cially giv­en that they can find their way over ter­ri­to­ry nev­er be­fore en­coun­tered. 

To nav­i­gate, sci­en­tists say, birds re­quire a men­tal “map” (to tell them home is south, for ex­am­ple) and a “com­pass” (to tell them where south is), with the sun and the Earth’s mag­net­ic field be­ing the pre­ferred com­pass sys­tems. 

The map is in fact avail­a­ble in the at­mos­phere: odors and winds, ac­cord­ing to the new find­ings pub­lished in Bio­geo­sciences, a jour­nal of the Eu­ro­pe­an Geo­sciences Un­ion. The study found that computer-generated “vir­tual pi­geons” could find their way home like real ones us­ing only da­ta meas­ured from the ac­tu­al at­mos­phere.

Ex­pe­ri­ments over the past 40 years have shown that hom­ing pi­geons get dis­ori­ented when their sense of smell is im­pa­ired or when they don’t have ac­cess to nat­u­ral winds at their home site. But many re­search­ers were not con­vinced that wind-borne smells could pro­vide enough in­form­ati­on to make the pi­geons’ map. 

Now, Hans Wall­raff of the Max Planck In­sti­tute for Or­nith­ol­o­gy in See­wiesen, Germany, has found that the at­mos­phere does con­tain such in­form­ati­on.

In pre­vi­ous re­search, Wall­raff col­lect­ed air sam­ples at over 90 sites with­in 200 km (125 miles) of a form­er pi­geon loft near Würzburg in south­ern Germany. The sam­ples in­di­cat­ed that the rel­ati­onships among the lev­els of cer­tain scent-producing chem­i­cals in­crease or de­crease along spe­cif­ic 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 said. 

But a pi­geon that has nev­er left its loft does not know in what directi­ons what changes oc­cur – un­less it has been ex­posed to winds at its home site, he added.

At home, a bird is thought to as­so­ci­ate cer­tain smells with par­tic­u­lar wind directi­ons. “If the per­cent­age of com­pound A in­creases with south­erly winds, a pi­geon liv­ing in a loft in Würzburg learns this wind-correlated in­crease. If re­leased at a site some 100 km south of home, the bird smells that the ra­tio of com­pound A is above what it is on av­er­age at its loft and flies north,” Wall­raff ex­plained. 

To use an anal­o­gy, a per­son in Mu­nich could smell an Al­pine breeze when there is wind blow­ing from the south. When moved clos­er to the moun­tains, they would de­tect a strong Al­pine scent and re­mem­ber that, at home, that smell is as­so­ci­ated with south­erly winds: the per­son would know that, rough­ly, they needed to trav­el north to find home.

In his pa­per, Wall­raff pre­sented a mod­el show­ing that “vir­tual pi­geons” with only knowl­edge of winds and odors at home, can find their way back to their lofts by us­ing real at­mos­pher­ic da­ta.


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Smell may account for the extraordinary navigational skills of homing pigeons, a study said. Homing pigeons are domesticated pigeons bred for their ability to find their way to their home lofts when moved away long distances—in some cases, as much as one-seventh the width of the Earth. How they manage to find their way back is still debated, especially given that they can find their way over territory never before encountered. To navigate, scientists say, birds require a mental “map” (to tell them home is south, for example) and a “compass” (to tell them where south is), with the sun and the Earth’s magnetic field being the preferred compass systems. The map is in fact available in the atmosphere: odors and winds, according to the new findings published in Biogeosciences, a journal of the European Geosciences Union. The study found that computer-generated “virtual pigeons” could find their way home like real ones using only data measured from the actual atmosphere. Experiments over the past 40 years have shown that homing pigeons get disoriented when their sense of smell is impaired or when they don’t have access to natural winds at their home site. But many researchers were not convinced that wind-borne smells could provide enough information to make the pigeons’ map. Now, Hans Wallraff of the Max Planck Institute for Ornithology in Seewiesen, Germany, has found that the atmosphere does contain such information. In previous research, Wallraff collected air samples at over 90 sites within 200 km (125 miles) of a former pigeon loft near Würzburg in southern Germany. The samples indicated that the relationships among the levels of certain scent-producing chemicals increase or decrease along specific 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. But a pigeon that has never left its loft does not know in what directions what changes occur – unless it has been exposed to winds at its home site, he added. At home, a bird is thought to associate certain smells with particular wind directions. “If the percentage of compound A increases with southerly winds, a pigeon living in a loft in Würzburg learns this wind-correlated increase. If released at a site some 100 km south of home, the bird smells that the ratio of compound A is above what it is on average at its loft and flies north,” Wallraff explained. To use an analogy, a person in Munich could smell an Alpine breeze when there is wind blowing from the south. When moved closer to the mountains, they would detect a strong Alpine scent and remember that, at home, that smell is associated with southerly winds: the person would know that, roughly, they needed to travel north to find home. In his paper, Wallraff presented a model showing that “virtual pigeons” with only knowledge of winds and odors at home, can find their way back to their lofts by using real atmospheric data. “My virtual pigeons served as tools to select those volatile compounds whose spatial distributions, combined with variations dependent on wind direction, were most suitable for homeward navigation,” said Wallraff.