Do Chickens Have a Sense of Smell?

Chickens don’t have a nose to wriggle up, like a human who smells something odd or interesting. Neither to they noticeably sniff at things, like a dog does. Nevertheless, chickens have a keen sense of smell. And it’s likely every bit as good as a human’s, if not better.

Olfaction System

Olfaction is a fancy word for sense of smell. As it turns out, a chicken’s olfaction system isn’t all that different from a human’s. A chicken has two nostrils through which it breathes. The air it breathes moves through a fully developed nasal cavity before reaching olfactory receptors that connect to an olfactory bulb.

The olfactory bulb is the brain’s smell center. And a chicken’s olfactory bulb is structurally similar to that of humans and other vertebrates.

The size of the olfactory bulb relative to the size of the brain indicates the bird’s degree of odor discrimination. Ducks and geese have larger olfactory bulbs than chickens and turkeys. Therefore, odor perception in waterfowl apparently is even more refined than in chickens.

The olfactory receptors, also called smell receptors, are a complex family of genes. This family is one of the largest gene families in vertebrates.

A chicken has about 350 receptors, all of which are fully functional. In contrast, a human has some 1,000 receptors, but only about 350 are functional. The remainder are inactive. That we humans don’t use all our receptors, while a chicken does, indicates that sense of smell is more important to a chicken than to a human.

But it gets even more interesting. Based on an ability to recognize structurally related scents, receptors fall into three major subfamilies — alpha, gamma, and gamma-c. All mammals, reptiles, and birds share the first two subfamilies. But the gamma-c receptors are unique to birds.

Not only that, but a chicken’s gamma-c receptors far outnumber its receptors in the other two subfamilies. Which begs the question, can chickens smell things we human’s can’t?

Sense of Smell and Body Odor

Chicks start smelling their environment even before they hatch. Their early survival depends on a learned preference for the familiar odors of “home” and “mama.”

The body odor in chickens, as in humans, relates on one level to environment and diet. On a deeper level is a baseline odor that reveals individual identity and state of health.

That probably sounds far fetched unless you’re familiar with the group of genes making up the major histocompatibility complex. This mouthful of genes forms the genotype of a body’s immune system. The genes express themselves in odors emitted as the body’s baseline scent.

Much of a chicken’s body odor is imbedded in preen oil. This waxy oil contains chemical odors birds can detect. The amount and chemical composition of preen oil varies both seasonally and between hens and roosters. Preen oil odors reveal a chicken’s individual identity, sex, reproductive state, and relationship to other chickens in the flock.

That a chicken can recognize dozens of individuals within a flock is likely, at least in part, due to body odor. When a rooster’s engages in wing-flapping and feather-ruffling during courtship displays, he may well be transmitting his body odor in the direction of his chosen hen.

Olfaction in chickens, humans, and other animals is an emerging science. So far we know that, indeed, chickens have a sense of smell. And their sense of smell influences much more of their ecological, social, and sexual behavior than has so far been discovered.