For the Birds Radio Program: Hearts
Laura celebrates her wedding anniversary thinking about bird hearts. (4:02) (Date confirmed) (Reworked from 3-18-88)
Today is my nineteenth wedding anniversary. Birds don’t really get married, much less celebrate wedding anniversaries, but I wanted to mark the occasion with something romantic, so I decided to talk about hearts.
Hearts and birds somehow go together. The poet Robinson Jeffers said to give your heart to Hawks. Othello preferred to wear his heart on his sleeve for daws to peck at, daws referring to the Eurasian Jackdaw, a relative of our crow. Edgar Allan Poe begged his raven to “Take thy beak from out my heart.” Christina Rosetti was definitely having a better day when she said that her heart was like a singing bird.
Bird hearts are every bit as interesting as human hearts. The avian heart is one of the most powerful pumps known to man, and the hummingbird heart is one of the most powerful of all. Ornithologists Joel Peters wrote of a hummingbird:
Darting, hovering helicopter
Fueling at a flower,
Tell me how your engine heart
Generates such power!
Like mammals, birds have a four-chambered heart which completely separates the circulation routes for arterial and venous blood. But a mammal heart is puny and weak compared to the heart of a comparably-sized bird. A robin’s heart beats 570 times every minute. A sleeping chickadee’s heart beats from 522 to 675 times a minute, and once it is awake and flying, the rate doubles to more than a thousand beats a minute. An active Blue-throated Hummingbird’s heart races at 1,260. Our own Ruby-throated Hummingbird, while resting in a dark chamber, has a rate of 614, and no one has developed a technique for measuring it when the hummer is awake. While incubating eggs, a bird’s heart rate jumps, especially on cool nights. a House Wren’s heart beats 455 times a minute at rest normally, but goes up to 701 while sitting on a nest.
Not only do birds have rapid heart beats; they also have extraordinarily high blood pressure. The systolic pressure for a starling is 180 mm, and for a canary is 220. In comparison, a healthy person’s systolic pressure should not exceed 150. A bird’s high pressure pushes the blood through the body very quickly. It takes only about 6 seconds for blood to make a complete circuit through the body of an adult chicken.
This high blood pressure also pushes a bird’s heart just about to the limits of mechanical safety. Many banders have caught birds in their nets only to have them die of heart attacks in their hands. One cardinal, who died after an exhausting territorial squabble, was examined carefully, but no outer wounds were present. A post-mortem revealed a 7 mm wound in the ventricle, probably caused by the great pressure built up during the excitement. Although post-mortems are not often done on birds, a Field Sparrow with a ruptured aorta and a Bald Eagle with a ruptured right auricle were also apparently victims of excitement.
In selectively breeding domestic turkeys for rapid growth and heavy meat production, breeders unwittingly also selected strains that have high blood pressure and weak arteries. As a result, some turkey flocks have suffered high mortalities from aortic rupture followed by internal hemorrhaging. To prevent this, a tranquilizing drug is often added to feed mixtures to reduce nervous tension and lower blood pressure. Perhaps some of that tranquilizer should have been added to the laboratory vat in which was kept alive Bill Cosby’s notorious Chicken Heart.