It was once believed that birds had little to no sense of smell, relying instead on keen eyesight and hearing. However, scientific research has challenged this notion, revealing that birds do possess a sense of smell, which plays an important role in many species’ lives. Research over the past several decades has revealed a diverse range of olfactory capabilities across avian species.
The Avian Olfactory System
Birds possess the necessary biological structures for olfaction, similar to other vertebrates. Their nasal cavity contains an olfactory epithelium, which houses the primary receptor neurons responsible for detecting odors. These receptors connect to paired olfactory bulbs located at the front of the brain.
The size of these olfactory bulbs varies considerably among species. For instance, in some songbirds, they might be as small as 3% of the brain, while in certain seabirds, they can be up to 37%. This variation correlates with the bird’s reliance on smell; species with larger bulbs typically have a more developed sense of smell. All birds, regardless of bulb size, possess some capacity for smell.
Molecular studies further support these anatomical findings, showing that a larger olfactory bulb size is linked to a greater number of genes encoding olfactory receptors. This indicates that the diversity in olfactory capabilities among birds is a result of evolutionary adaptations to their specific environments and lifestyles. Nocturnal birds, for instance, often exhibit larger olfactory bulbs, suggesting an increased reliance on smell in low-light conditions where vision is less effective.
How Birds Use Their Sense of Smell
The sense of smell in birds serves a variety of functions, ranging from finding food to navigating vast distances and even influencing social interactions. This sensory ability is particularly pronounced in species where visual cues are limited or unreliable.
Foraging is a prominent use of olfaction for many bird species. Turkey vultures, for example, possess an exceptional sense of smell, detecting mercaptans—gases released by decaying carcasses—from considerable distances, even when hidden from sight. This allows them to efficiently locate carrion, contributing to their role as scavengers.
Kiwis, flightless nocturnal birds, use their highly developed sense of smell to find invertebrates and worms underground by probing the forest floor with their long beaks, which have nostrils at the tip. Seabirds like petrels and albatrosses, known as “tubenoses,” employ their keen sense of smell to locate prey such as krill and fish in the vast ocean. They detect compounds like dimethyl sulfide, released when plankton, a food source for krill, is consumed.
Beyond foraging, smell also plays a role in navigation for some birds. Homing pigeons, for instance, are believed to construct an “olfactory map” of their environment, associating airborne odors with specific directions around their home loft. This allows them to navigate back to their roost even from unfamiliar locations. While the exact mechanisms are still being studied, evidence suggests that olfactory cues contribute to their homing abilities.
The sense of smell also aids in predator detection. Some bird species can detect chemical cues emitted by predators, such as mustelids, and may avoid nesting in areas where these scents are present. This ability helps them assess predation risk.
In social contexts, birds use scent for individual recognition, mate selection, and identifying offspring. For example, some seabirds recognize individual scents, and species like black-legged kittiwakes may use odor to assess genetic compatibility and avoid mating with close relatives. Scents from a bird’s preen gland can convey information about reproductive health and genetic quality, influencing mate choice. Crested auklets even produce a distinct citrus-like scent during courtship displays, potentially acting as an “olfactory ornament.”