For the Birds Radio Program: Exsanguination

Original Air Date: Oct. 12, 1994

How much blood does a bird have? And how do we know this? (3:36) (I think it’s correct that I reworked the script from 2-7-94)

Audio missing


As a student of avian physiology, I’ve learned some things I’d just as soon not discovered. For example, I’ve long known that in baby birds, the body is about 12 percent blood while adult bodies are only about 6 percent blood. The amount of blood in an animal is a critical factor when calculating just how much of a particular medication to administer, so this basic fact is important. But I was nonetheless taken aback to learn just how scientists determined it. There’s a fancy name for the process: exsanguination, which literally means letting the blood out, through a needle inserted into a blood vessel This is done while the bird is still alive, with a working heart to cooperatively pump away as the vital fluid leaks into the researcher’s container.

Oddly, birds never go into shock even after losing huge quantities of blood, and survive blood loss much better than mammals do, apparently because they efficiently detect blood loss and constrict their blood vessels to maintain blood pressure. A duck can withstand the rapid loss of 12 percent of its total blood volume with only a slight drop in blood pressure, ad if, after a few days, it is bled again, it can lose an even greater quantity before its pressure drops again to the same level. One researcher learned that rats, cats, and dogs could lose only half as much as pheasants, crows, hens, ducks, or pigeons before dying. When I saw the graph showing the results of the study, all I could do was wonder how anyone could sit by passively as the life literally drained out of these animals. Was that little fragment of knowledge really worth the cost of learning it?

Fortunately, much of this basic research was done long ago, though the study of blood loss fatality in birds was just done in 1969. Some animal research not only increases our knowledge and helps our own species, but also provides knowledge that improves the lives and health of our pets and those wild creatures that are treated by veterinarians or rehabilitators. Outright cruelty makes all but a few researchers uncomfortable, and many refuse to consider experiments that are unjustifiable or only remotely justifiable, though some arrogantly consider any question that they can think up worth getting an answer to at any cost.

When science and government work together, they can send humans to the moon and eradicate smallpox, but science aided by government, or government aided by science, can also do incalculable harm. Radiation research on humans devised by American scientists and governmental authorities is no more justifiable than Nazi medical experimentation on human subjects—somehow bleeding a chicken seems pretty gentle in comparison. Science—that is, the human mind’s capacity for asking questions and devising ways of learning the answers—is what brings about giant steps for mankind. But only the human heart can tell us whether each of those giant steps will carry us forward or backward.