Birds have a sense of smell just like humans and other animals do. However, not all bird species rely on their sense of smell to the same degree. Birds use their sense of smell for a variety of purposes including locating food, avoiding predators, navigation, and social communication.
The Bird Nose and Olfactory System
Birds have nostrils, just like humans do, that allow air and odors to enter the nose and come into contact with receptor cells. Inside a bird’s nasal chamber are folds and scrolls of delicate tissue called turbinates which contain the olfactory receptors. The olfactory receptors detect odor molecules and transmit signals to the brain which identifies the smell. The area of the bird’s brain that processes smells is called the olfactory bulb.
Birds that rely heavily on their sense of smell often have larger olfactory bulbs in their brains and more olfactory receptor genes than birds that do not rely on smell as much. For example, kiwi birds which locate food by smell have 100 times more olfactory receptor genes than zebra finches which use sight rather than smell to locate food.
In addition to the main olfactory system, birds also have a second olfactory system located in their vomeronasal organ. The vomeronasal organ detects pheromones which are chemical signals that communicate information between members of the same species. It plays an important role in social communication and courtship displays in birds.
Which Birds Have a Good Sense of Smell?
Scientists have tested the relative sense of smell in various bird species by measuring the size of their olfactory bulbs and analyzing their genome for active olfactory receptor genes. Birds with larger olfactory bulbs and more olfactory receptor genes generally have a better sense of smell.
Some birds with an excellent sense of smell include:
- Kiwis – They have 100 times more olfactory receptor genes than birds like finches. Kiwis use their keen sense of smell to locate food at night when vision is poor.
- Vultures – Rely on their sharp sense of smell to locate dead and decaying animals.
- Tubenosed seabirds – Such as albatrosses, shearwaters and petrels have a highly developed sense of smell which they use to locate food.
- Terns – Use smell to recognize their chicks when returning to the crowded breeding colony.
- Parrots – Have a large olfactory bulb and many active olfactory receptor genes compared to other birds.
- Pigeons – Use smell to navigate on long flights back to their nest.
On the other hand, some birds have very little sense of smell including swifts, swallows, herons, owls, eagles, hawks and hummingbirds. These species tend to rely more on sight than smell.
How Birds Use Their Sense of Smell
Finding Food
Some birds use their sense of smell to locate food sources. Scavenger birds like vultures can smell decaying meat and garbage from great distances. Kiwis probe the ground with their long beaks sniffing for worms, insects and other invertebrates to eat. Seabirds such as petrels and shearwaters use smell to locate schools of fish and krill.
Avoiding Predators
Prey animals like birds often have a heightened sense of smell to detect approaching predators. Seabirds called Leach’s storm petrels can smell the odor of predators like owls from 50 yards away. This gives them time to escape the owl ambush. Some birds may also recognize the scent of their own species members after a predator attack and take avoidance measures.
Navigation
Experiments have shown that birds may use their sense of smell for true navigation by identifying unique odors from different locations. One experiment showed that pigeons deprived of smell could still navigate home visually. However, their flight paths were less direct than birds with an intact sense of smell, indicating smell contributes to navigational efficiency.
Communication
Birds communicate with smell in two major ways. First, preening oil secreted from the uropygial gland located near a bird’s tail contains waxes, fatty acids and alcohols that give each bird a unique odor signature. Birds can recognize their own mate or chicks by odor. Second, some birds release pheromones or scents that communicate information. For example, female black-legged kittiwakes release a pheromone from their preen gland to signal readiness for copulation.
Avoiding Bad Food
Along with taste, the sense of smell helps warn birds away from toxic or spoiled food sources that could make them sick. Vultures avoid the scent of decay and feces to prevent eating diseased meat. Seabirds avoid fish that contain defensive chemicals which the birds can detect by smell.
Hygiene
By sniffing their feathers and skin, birds use smell to assess if they need to apply preen oil or take a dust bath to clean themselves. The uropygial gland secretes preen oil that gives feathers water resistance and contains antibacterial and antifungal properties to inhibit microbes. Birds know when they need to apply more after exposure to lots of water or dust.
Why Some Birds Have a Poor Sense of Smell
Birds like parrots, seabirds and vultures have excellent senses of smell. So why do some species like falcons and songbirds have such a poor sense of smell?
There are a few key reasons some birds do not rely on smell very much:
- They occupy ecological niches where other senses like vision are more useful for survival than smell. For example, hawks use vision rather than smell to locate prey during flight.
- They eat foods like seeds, nuts and fruit where scent is less important than sight for finding food.
- They are active during the day rather than at night when vision is reduced.
- They do not eat carrion which requires locating by smell.
- They have alternative adaptations for navigation like magnetic senses rather than relying on smell maps.
Birds tend to evolve a good sense of smell only when it provides a strong advantage for survival in that particular niche. Otherwise vision, hearing and other senses tend to dominate.
Smell Experiments in Birds
Scientists have performed some interesting experiments to study the sense of smell in birds:
- Nostril Plugging – Researchers temporarily plug the nostrils of petrels and find they can no longer locate their nest burrows or avoid predators.
- Nerve Cutting – Cutting the olfactory nerve eliminates or reduces responses to smell.
- Odor Habituation – Exposing birds to the same odor again and again decreases their response, indicating they can detect and remember smells.
- Y-maze Test – Given a choice between two arms of a Y-shaped maze containing different odors, birds consistently choose or avoid particular smells.
- Gene Knockout – Silencing olfactory receptor genes through gene knockout or mutation reduces smell response.
These experiments demonstrate birds do have functioning olfactory systems and sense of smell they use in behavioral responses.
Smell and Bird Evolution
Studying the sense of smell provides clues to how birds evolved. Modern birds or Neornithes evolved from feathered theropod dinosaurs around 150 million years ago during the Jurassic period. Theropod dinosaurs likely had fairly good senses of smell.
Later during the Cretaceous period, a group of Neornithes called Neoaves evolved and radiated into the vast majority of modern bird groups. Analysis shows different groups of Neoaves started losing olfactory receptor genes and grew smaller olfactory bulbs over evolution as some lineages came to rely more on other senses like vision rather than smell.
However, other lineages like kiwis and petrels maintained and even strengthened olfactory abilities as smell became a key adaptation for their niche. Differences in olfactory anatomy and genes among modern birds reflect their ancient evolutionary trajectories.
Conclusion
While not all birds rely heavily on it, the sense of smell is important for many avian species. Birds evolved from theropod dinosaurs which had fairly good smell. While some modern birds reduced their olfactory systems as vision became more central, others maintained or improved smell ability in order to locate food, avoid danger, navigate, and communicate. Birds like kiwis, vultures, petrels and parrots are strongly smell-dependent. Studies of olfactory genes and anatomy help reveal the evolutionary history of birds. Smell provides an essential sensory capacity for birds that occupy niches where odor cues are critical to their survival success.