Birds were long thought to rely primarily on sight and hearing, with their sense of smell considered almost nonexistent. However, research now shows birds possess a functional sense of smell, though its importance varies greatly among species. This ability plays a role in finding food, navigating, and even social behaviors.
Dispelling a Common Myth
The myth that birds lack a sense of smell originated from early observations focusing on their strong visual and auditory senses. For example, 19th-century naturalists like John James Audubon conducted experiments where turkey vultures seemingly failed to find hidden carrion, concluding sight was their primary tool. This view persisted for over a century. However, these early studies often had methodological flaws. Modern research now shows that while sight and hearing are prominent, olfaction is indeed present and functional in birds, albeit to varying degrees.
The Avian Olfactory System
A bird’s sense of smell is structurally similar to that of mammals and other vertebrates. Birds have external nostrils, called nares, usually near the base of their upper beak. Air enters these nares, passing through nasal cavities to the olfactory epithelium, which contains specialized receptors.
These receptors bind with odor molecules, sending signals to the olfactory bulbs at the front of the brain that process scent. The size of their olfactory bulbs relative to brain size indicates the importance of smell, with larger bulbs correlating to a more developed sense.
Masters of Scent: Birds with Keen Olfaction
Some bird species have a remarkably acute sense of smell. Turkey vultures, for instance, detect the scent of decaying carcasses, specifically ethyl mercaptan, from over a mile away. Their large olfactory bulbs, four times larger than those of black vultures, enable them to locate hidden food sources even under dense forest canopies. This allows them to find carrion other scavengers might miss.
The kiwi, a nocturnal, flightless bird native to New Zealand, is another example. Uniquely, kiwis have nostrils at the tip of their long beaks, which they use to probe the forest floor for earthworms and other invertebrates. Their highly developed olfactory system, with a large olfactory bulb, compensates for poor eyesight in their dark habitat. Research shows kiwis can detect earthworms up to three centimeters underground, demonstrating precise scent-based foraging.
Seabirds, particularly tube-nosed albatrosses, petrels, and shearwaters, also have exceptional olfactory capabilities. Over vast oceans, where visual food cues are scarce, these birds rely on smell. They are highly sensitive to dimethyl sulfide (DMS), a gas released by feeding zooplankton, indicating productive feeding grounds. Beyond foraging, some seabirds, like Cory’s shearwaters, use an “olfactory map” to navigate back to remote breeding colonies, even over hundreds of miles. Studies show impaired smell significantly hinders their navigation.
The Varied Spectrum: Birds with Limited Olfaction
While some birds excel at scent, olfaction is less prominent for many species relying on vision and hearing. Songbirds, woodpeckers, pelicans, and parrots were long assumed to have poor smell, partly due to smaller olfactory bulbs. Their foraging and social interactions often depend more on visual cues, like identifying distant prey, or auditory signals, like complex songs. This reflects their ecological niches and adaptations.
Despite less acute smell than specialists, recent studies reveal subtle but important uses of olfaction even in these species. For example, zebra finch fledglings distinguish their nests by scent, suggesting a role in spatial orientation. European starlings and blue tits select aromatic herbs for nests, which may deter parasites, indicating a functional application of smell. Thus, while less dominant, smell is a widespread, functional trait across the diverse avian world.