Can Birds Smell? Vultures, Kiwis and Seabirds

Where did the idea that birds cannot smell come from?

The belief goes back at least to the 1820s, when the bird artist John James Audubon reported experiments in which vultures ignored a hidden rotting carcass but were attracted to a stuffed deer skin. He concluded that vultures hunt by sight alone. Later researchers have pointed out that Audubon was probably watching black vultures, which do rely mostly on sight, rather than turkey vultures.

Birds also seemed to be built for vision. Most have huge eyes, and the part of the brain that processes smell, the olfactory bulb, looks small next to that of a dog or a rat. For more than a century, textbooks repeated that birds were nearly “anosmic”, or unable to smell.

That view began to change in the 1960s. The American researcher Betsy Bang measured the olfactory bulbs of more than 100 bird species and found that some, such as vultures, kiwis and seabirds, had large ones. Since then, studies of behavior and of bird genes have shown that smell plays a role in finding food, navigating, recognizing other birds and even choosing nest material.

How turkey vultures smell dead animals

The turkey vulture is the classic example of a bird that smells. It has one of the largest olfactory regions of any bird. Flying low over woodland, it can detect ethyl mercaptan, a sulfur-smelling gas released in the first stages of decay, and track it to a carcass hidden under trees.

In the 1960s the American ornithologist Kenneth Stager showed experimentally that turkey vultures are attracted by smell. He also recorded a story told by gas company workers: ethyl mercaptan was added to natural gas so that leaks could be smelled, and turkey vultures were reported gathering over places where a pipeline was leaking.

Turkey vultures prefer fairly fresh carcasses, and the smell of the early stages of decay is the signal that leads them there. The closely related lesser and greater yellow-headed vultures share this ability. Other New World vultures, such as the black vulture and the condors, have a much weaker sense of smell and often follow turkey vultures to food. Even soaring vultures that rely on sight are mostly searching, not waiting, as explained in why do vultures circle?.

How kiwis sniff out worms

New Zealand’s kiwis, including the North Island brown kiwi, are the only birds in the world with nostrils at the very tip of the bill. At night, a kiwi walks through the forest tapping and probing the leaf litter and soil, and it often sniffs loudly as it goes.

Experiments in the late 1960s showed that kiwis could find food buried in the ground using smell alone, choosing containers that held food over empty ones. Kiwis have small eyes and poor eyesight, and they also use touch-sensitive pits at the bill tip and their hearing to locate prey. Smell is one tool among several, but it is unusually important for a bird.

Kiwis eat earthworms, beetle larvae, spiders and other invertebrates, plus some fallen fruit. Their combination of tiny eyes, whisker-like feathers around the face and a keen nose has led some biologists to describe them as birds that live like small mammals.

How albatrosses and seabirds smell food at sea

Albatrosses, petrels and shearwaters belong to a group known as tubenoses, because their nostrils sit inside raised tubes on the bill. They have some of the largest olfactory bulbs of all birds, and they use smell to search the vast, featureless ocean for food.

One key scent is dimethyl sulfide, a compound released when tiny marine algae are eaten by krill and other grazers. In the 1990s the American biologist Gabrielle Nevitt showed that some petrels and prions are attracted to this smell, which marks areas where their prey is likely to be. Other tubenoses respond to the fishy odor of oils from krill and squid.

A 2008 tracking study of wandering albatrosses, which carried GPS loggers, found that the birds often approached prey by flying upwind in a zigzag pattern, the way an animal follows a scent trail. The researchers estimated that a large share of the prey the albatrosses caught was first detected by smell rather than sight.

Other birds that use smell

Smell is not limited to a few specialists. Homing pigeons appear to use airborne odors as one of their navigation cues, and pigeons whose sense of smell was blocked often had more trouble returning home from unfamiliar places. Some seabirds, such as petrels nesting in burrows, find their own burrow in the dark partly by its smell.

Studies of songbirds suggest they can tell individuals apart by scent, and some species line their nests with aromatic plants that may help keep parasites in check. Chickens and ducks react to smells in their food and surroundings. Genetic studies have found hundreds of olfactory receptor genes in many birds, including species once thought to have almost no sense of smell.

How a bird’s sense of smell compares with ours

Birds that rely on smell are not all better smellers than people for every odor, and most birds still depend mainly on vision and hearing. But a turkey vulture can find a carcass under a forest canopy from the air, and an albatross can detect food over many kilometers of ocean. For those tasks, their noses are far more useful than ours.