For a long time, the common belief was that birds possessed little to no sense of smell, relying almost entirely on their exceptional vision. This idea has been largely overturned by decades of scientific research, which confirms that all birds have the anatomical structures for olfaction. The question is no longer whether birds can smell, but rather how effective this sense is and how far its reach extends across the avian world. The effectiveness of a bird’s sense of smell is highly variable, depending on the species’ lifestyle and ecological needs.
The Science of Avian Olfaction
Air enters through the external nostrils, or nares, and passes through a series of internal nasal chambers called conchae. These chambers are lined with the olfactory epithelium, which contains the receptor cells that detect airborne chemical compounds.
These receptor cells transmit signals via the olfactory nerves directly to the olfactory bulb, a structure located at the front of the forebrain. The size of the olfactory bulb relative to the rest of the brain is a reliable indicator of a species’ reliance on smell. Birds with a highly developed sense of smell possess a proportionally larger olfactory bulb.
The complexity of the nasal cavity also plays a role, as a more convoluted or scrolled posterior concha increases the surface area of the scent-detecting olfactory epithelium. While most birds rely on passive inspiration to draw air over the receptors, some species, like the kiwi, have specialized nostrils near the tip of the bill and can actively “sniff” the ground.
Range and Variation in Bird Smell
Birds with the most acute sense of smell, such as the Procellariiformes (tube-nosed seabirds like petrels and albatrosses), have olfactory bulbs that can be over 37% the size of their cerebral hemispheres. These seabirds can detect the scent of dimethyl sulfide (DMS), a compound released when plankton is consumed by krill, from distances of up to 12 miles away.
Turkey Vultures also possess a highly developed olfactory system, with a complex, scrolled concha and a large olfactory bulb. They are known to detect the scent of ethyl mercaptan, a gas produced by decaying animal matter, from over a mile away. This allows them to locate fresh carrion hidden beneath a forest canopy, where sight would be ineffective. The nocturnal, flightless kiwi, which has poor eyesight, uses its sense of smell to locate earthworms and insects underground, essentially sniffing out its prey.
In contrast, many songbirds (Passeriformes) and parrots have relatively small olfactory bulbs, sometimes less than 5% of the cerebral hemisphere size. These species rely primarily on their exceptional vision and hearing for survival and foraging. However, even in these small-bulbed birds, olfaction is not absent, and they use it for more localized, short-range tasks. The range of a bird’s smell is therefore directly proportional to the evolutionary importance of scent in its daily life.
Practical Uses of Smell in Bird Life
Foraging is a primary use, with species like the Northern Fulmar being attracted to fish oils and squid from downwind. The ability to detect these specific chemical cues allows them to efficiently exploit food resources that are otherwise invisible.
Olfaction also plays a significant role in navigation, particularly for seabirds and homing pigeons. Experiments have shown that seabirds like Scopoli’s shearwaters use an “olfactory map” of atmospheric odors to navigate over the open ocean. Homing pigeons are also believed to associate wind-borne odors with specific directions, helping them find their way back to their loft after being displaced.
Furthermore, scent cues are used for social and reproductive purposes, even in species with smaller olfactory bulbs. Crested Auklets, for example, engage in social rituals where they bury their faces in the citrus-scented feathers of other birds, suggesting the use of scent for mate assessment or social bonding. Some songbirds, such as European Starlings, use smell to select aromatic plants for their nests, which may help reduce parasite loads.