Reflections in Nature: Scientists have used experiments to determine if birds can smell
Those of you that are continually filling your bird feeders have surely noticed that birds have a seed preference. For example, many seed bags show a cardinal eating sunflower seeds. Does the cardinal prefer the sunflower seed because of its taste, color or smell?
For more than a century, it has been debated whether or not birds can smell. Scientists have made relatively few experiments concerning the olfaction of birds. Olfaction, which pertains to or is used in smelling, comes from two Latin words: olere, meaning smell, and facere, meaning to make.
The sense of smell is one of the oldest of all animal senses. It is not as difficult to measure in animals as it is in birds. Most studies on birds have been inconclusive. Studies of the olfactory lobes in the brains of birds show they vary considerably in size. They are larger in ducks than in songbirds. There is one olfactory lobe in the house sparrow and two in the crow. However, the olfactory lobes of some birds are so large that they become field observation points, suggesting that they have a good sense of smell.
The olfactory lobes of the brain are well developed in the emu and goose. A study done in the Antarctic on the behavior of the albatross, skua and petrel strongly suggested that these seabirds can smell meat, blood and hot fat on the sea. The New Zealand flightless kiwi has large olfactory lobes that are comparable in structure with those in animals. The kiwi has weak eyesight and is believed to find its favorite food, of earthworms, by smell.
The turkey vulture, which also finds its food by smell, has the largest olfactory lobes and largest nostrils of all the new world vultures. In one study, dead animals were picked up and hidden in bushes and hollow trees. With the aid of wind, the odor of the hidden carcasses reached the turkey vultures, while in low-altitude hunting flights, of 100-200 feet above the ground. To make the test more exact, the carcasses were placed inside a unit with a blower used to waft the odors of the dead animals from the ground into the sky. The dead animals were put out at night to prevent the day flying vultures from seeing the carcasses being hidden. During the following day, large numbers of vultures gathered around the units. These tests proved that turkey vultures find their food first by odor and then by sight. In similar tests done with other vultures, it was found that they depend solely on sight to locate food.
Studies done on the California condor showed that smell played only a minor role, if any, in finding food.
In a study done on the size of the olfactory bulb in 108 species of birds, it was concluded that smell is relatively unimportant. Other studies concluded that most birds apparently have adequate olfactory organs, however, in some species the sense of smell is poorly developed and plays little or no part in their lives.
Taste is the sense by which certain qualities, such as an acid, bitter, sweet and salty, are distinguished. The chemical stimulus of taste is brought about by the contact of these items with the taste buds in the mouth
Due to their lack of teeth most birds bolt their food quickly. Birds have a small number of taste buds known as ovoid clusters of chemical sensory receptors that are mostly in the soft area at the base of a bird’s tongue. However, a parrot’s tongue is fleshy and has taste buds. Some parrots have 400 or more taste buds.
Compare this to rabbits (approximately 17,000 taste buds), humans (about 9,000), chickens (24) and pigeons (eight). Most species of birds are said to have 30-70 taste buds.
It was found in tests done on tame pigeons they could detect the difference between starch and protein. Pigeons refused to eat kernels of corn after the protein rich eye had been cut out. This study pointed out that humans, with 9,000 taste buds, could not distinguish between starch and protein in a kernel of corn, while seeming to prove that although birds have fewer taste buds, they are able to use these lesser numbers in evaluating their foods.
After four years of backyard feeding experiments on 43 species of wild free-roaming songbirds of North America, it was concluded that birds definitely first sampled the foods offered before eating. From this long series of experiments, it was concluded that birds selected their food chiefly on the basis of taste while color, shape and texture were not significant under the conditions of the experiment. Size was a factor only when the seed or fruit was too large to be swallowed.
In the last two decades, research has shown that many birds do react to a variety of taste stimuli; however, it has not shown what degree of taste sensitivity they possess and how this affects selection of food.
Even without all this research, I’m sure we are aware that the birds visiting our feeders do have preferences for certain seeds and foods. We certainly have enjoyed the two hummingbirds visiting our scarlet bee balm flowers this summer. The question was were the visits because of the brilliant red color, the smell or the taste?
Bill Bower is a retired Pennsylvania Game Commission Wildlife Officer. Read his blog and listen to his podcasts on the outdoors at www.onemaningreen.com.