Bird migration is truly one of the most astonishing, and least understood, phenomena in the animal kingdom. Over the years, researchers have shown that some species navigate over thousands of miles using the position of the stars and the Earth’s magnetic field to find their way. One hypothesis is that sea birds, which spend time flying over featureless open water also use their sense of smell to navigate. Now, reports Helen Briggs at the BBC, a recent experiment concludes that sea birds do indeed sniff their way around the ocean, using a scent map to find their way.
Past researchers have tackled the topic of olfaction navigation by blocking the bird's sense of smell or disrupting their magnetic sense, according to a press release. They would move the creatures to unfamiliar parts of the ocean, and then monitored as the scent-impaired birds struggled to find their way home. But critics argued that moving the birds away from their home range might skew the results, and that the sensory deprivation might also impact other factors, like their ability to feed or their motivation to return to their home territory.
That’s why Oliver Padget of Oxford University's Department of Zoology designed a study to eliminate those concerns. He and his team captured 32 Scopoli’s shearwaters, a long distance migrating seabird, at a bird colony at Cala Morell on the Mediterranean island of Minorca.
The birds were divided into three groups: a control group, a magnet test group that were fitted with magnets and a scentless group that received a nasal irrigation of zinc sulfate—a compound that causes them to temporarily lose their sense of smell. All the birds were fitted with tiny GPS trackers. The animals were monitored for a month as they incubated eggs and raised chicks along the rocky coast.
As Briggs reports, the magnets and lack of smell did not seem to impact the birds as they foraged for food and fed their chicks. All of the creatures gained weight at a similar rate. However, the birds without a sense of smell behaved differently than the other birds on long-range foraging trips over open water. After spending time filling up along the Catalan coast, for instance, the irrigated birds showed markedly different flight patterns while heading back to the colony, flying in straight lines that were poorly oriented compared to their free-sniffing friends. According to the release, it was as if they were following a compass bearing, but were unable to adjust their path while out of the site of land. The researchers published their results in the journal Scientific Reports.
The results confirm previous studies that found that the birds likely use their sense of smell to create an olfactory map of the ocean, which they can then use to navigate when visual clues are not available. “Our new study eliminates [objections to past work], meaning it will be very difficult in future to argue that olfaction is not involved in long-distance oceanic navigation in birds,” Padget tells Briggs.
The relationship between navigation and smell is surprising, especially since until relatively recently scientists believed that birds had no sense of smell at all, reports Michael Lipske at the National Wildlife Federation. It wasn’t until the 1960s that researchers began to find that some birds had a strong sense of smell and that seabirds, pigeons, kiwis and others rely on smell to find food, with albatrosses able to catch the scent of a good snack from 12 miles away.
And Shearwaters aren’t the only birds that use a sense of smell to navigate. It turns out, the pigeon’s prodigious homing ability is also related to its sense of smell and that the right nostril in particular is related to its olfactory navigation ability.
The situation is a bit different with songbirds and other feathered friends, which have very small olfactory bulbs (the brain structure involved in the sense of smell). While it’s unlikely they navigate or feed using a sense of smell, Lipske reports that recent experiments show that they are able to recognize relatives through smell and some species even choose which plants to nest in based on smell.
But for Shearwaters, they just have to follow their noses home.