Birds were long thought to rely primarily on exceptional vision and hearing, with an underdeveloped sense of smell. Modern research has challenged this belief, showing many bird species possess a functional, often acute, sense of smell. This ability plays a role in finding food and navigating vast distances.
How Birds Smell
Birds perceive scents through their olfactory system, which includes olfactory bulbs in their brains. The relative size of these bulbs indicates a species’ olfactory capabilities. While some birds have smaller olfactory bulbs, others, particularly those foraging in low-light or featureless environments, possess notably large ones. Larger olfactory bulbs correlate with a higher number of olfactory receptor genes, responsible for detecting specific odor molecules.
Scent molecules enter the bird’s nasal passages, contacting specialized olfactory receptors. These receptors bind to odor molecules, sending signals to the brain’s olfactory bulbs for processing. The presence of these receptors across all tested bird species confirms their ability to smell. Diversity in olfactory bulb size and the number of receptor genes across avian species reflects adaptations to their ecological niches and behaviors.
Birds with Keen Noses
Some bird species are renowned for their developed sense of smell, utilizing it for survival. Turkey vultures, for instance, locate carrion by detecting ethyl mercaptan from decaying flesh over significant distances, even under dense forest canopies. This acute sense allows them to find carcasses one to three days old, indicating a preference for fresher carrion.
Kiwis, nocturnal, flightless birds of New Zealand, possess an exceptional sense of smell, with nostrils at the tip of their long beaks. This adaptation allows them to probe the ground and sniff out invertebrates like earthworms. Their olfactory bulb is among the largest relative to their forebrain size, second only to the condor, highlighting smell’s importance in their foraging strategy.
Many procellariiform seabirds, such as petrels and albatrosses, exhibit a developed sense of smell. They detect dimethyl sulfide (DMS), released by phytoplankton grazed by krill and other prey. This allows them to locate productive foraging areas over vast ocean expanses, navigating an “olfactory landscape” to find food patches.
The Many Roles of Avian Scent
Beyond foraging, smell serves diverse functions in avian life, contributing to navigation, predator avoidance, and social interactions. Homing pigeons, for example, use olfactory cues to create an “odor map” of their environment, aiding their return to the loft from unfamiliar locations. They associate specific smells with wind directions, allowing them to deduce their position relative to home.
Birds also use smell to detect and avoid predators. Studies show some species, like great tits, recognize mustelid predator chemical signals and alter their behavior, such as avoiding nesting in areas where these scents are present. This ability to assess predation risk through smell is present even in young birds, suggesting an innate response.
Olfaction plays a role in avian social behaviors, including kin and mate recognition. Zebra finch fledglings distinguish between kin and non-kin based on olfactory cues. Birds also use scent to identify suitable mates. Research suggests species like black-legged kittiwakes and song sparrows assess genetic compatibility through partner odor profiles, often preferring mates with different genetic makeups for healthier offspring. Nest recognition can also involve olfactory cues, with female birds showing a preference for their own nest’s odor, particularly during the nestling phase.