For the Birds Radio Program: Do Birds Yawn? (Reworked)

Original Air Date: Nov. 5, 1997

Are birds really yawning, or is it simply a kind of jaw-stretch?

Duration: 4′09″


Yawning (From 1989)

(Recording of a Brandt’s or Peglagic Cormorant)

During the past hundred years ornithologists have discovered clues about many avian mysteries–such as how migrating birds know when to leave and how they find their way, and the mechanisms by which pesticides affect the nesting cycle. But for every answer there is another question, and so there are still mysteries. One of the great unanswered questions still facing ornithologists is whether birds yawn. I’ve done some hard-nosed investigative reporting with the help of the British Ornithologists’ Union’s Dictionary of Birds to bring you up to date on this important issue.

First of all, there’s no question that most species of birds open their beaks in a movement resembling a mammalian yawn, but no one has yet demonstrated whether or not this “jaw stretching ” also regularly includes the inhalation and exhalation of air. A prominent German ornithologist named Heinroth wrote a paper in 1930 proposing that “jaw stretching” is completely independent of any breathing movements, and that it thus cannot be considered a true yawn. Many students of animal behavior, including Konrad Lorenz, accepted his interpretation. But then, in 1967, in the most comprehensive study of yawning in any bird, two ornithologists clearly observed both inhaling and exhaling in yawning ostriches and published their findings in the journal of the American Ornithologists’ Union. In 1974, a scientist managed to distinguish both a true jaw-stretch, without any appreciable opening of the throat, and a true yawn, with definite inhalation of a breath of air, in both Brandt’s Cormorant and the Pelagic Cormorant. In 1977 an appropriately named Dr. Simmons detected both jaw-stretching and yawning in the Great Crested Grebe and the Brown Booby–presumably neither bird was resting on a Simmons beauty-rest mattress at the time.

It turns out that cormorants and boobies are the only birds in which jaw-stretching is easy to observe because in these families the upper bill can be flexed upwards at the naso-frontal hinge. In other birds it’s a lot harder to tell whether the birds are actually breathing when the beak is opened, and so naturally ornithologists have felt compelled to spend hours watching them and trying to figure it out. By 1985 detailed descriptions of yawn-like movements had been done for penguins, ducks, geese, plovers, Old World warblers, and finches. And there’s probably an ornithologist out there even as I speak who’s taking detailed notes about a thoroughly bored and sleepy blackbird.

Meanwhile, the whole physiological function of the true yawn, in birds or mammals, remains a mystery. It has been suggested that in mammals a yawn serves to purge the deeper parts of the lung of carbon dioxide, which accumulates during shallow, restful breathing. But some people dispute that argument since yawning never occurs during sleep. Filling the lungs with fresh air may be a way of enhancing alertness during a drowsy period, or of somehow speeding up the transition between sleep and an active state.

Meanwhile, if you want to dedicate your life to studying avian yawning, Dr. Peter Norman Ferns of the Zoology Department at the University College at Cardiff, Wales, cautions the casual observer not to confuse jaw-stretching and yawning with other gaping activities, such as panting, soliciting food, threatening displays, and persistent gaping due to a throat infected with syngamid nematodes, also known as gapeworms. If you’re going to study yawning at all, you better do it right.

(Recording of a Brandt’s or Peglagic Cormorant)

This is Laura Erickson, and this program has been “For the Birds.”