Flocks of red-winged blackbirds began arriving in the Chicago area about March 1. The earliest birds were males traveling in mixed flocks with grackles and cowbirds. Their arrival every year at this time is one of the first signs of spring, a harbinger of green leaves, bright flowers, balmy breezes, and tiger mosquitoes.
Redwings may be the most common birds in North America. They nest all over the continent, from Alaska to Central America. The average U.S. population has been estimated at nearly 200 million. Here in Illinois, they almost always head the list as the most numerous birds on our annual spring censuses.
They may also be the most studied birds in North America. A bibliography of publications since Audubon wrote about the bird a century and a half ago shows more than 700 studies of various aspects of the lives of redwings. In the decade from 1971 through 1980 alone, 349 studies were published, and through 1980, 75 students had written master's or doctoral theses on the species.
There are a number of reasons for all this attention. To start with, it is cheap to study redwings. No matter where you live in North America, redwings live there too. Redwings are also very visible birds. They aren't hidden in the crowns of tall trees. They nest in cattail marshes and in open upland situations, places where a careful observer concealed in a blind can watch every aspect of their lives.
In fact, you don't even need a blind to see most of a redwing's life. Sit quietly on a slope overlooking a cattail marsh anytime during the next couple of months, and you can learn a whole lot about the breeding cycle. The process is beginning right now, as the males begin to establish their territories by singing their gravel-voiced book-er-tee song and displaying their bright red epaulets.
An ideal marsh territory for a redwing would measure about 60 feet on a side and include both cattails and at least one tree to provide a singing perch. Students of redwing behavior have discovered that the borders of these territories are almost as precisely defined as the property lines in a human city. Working out the definitions requires a certain amount of conflict between neighbors. Most of these battles are fought symbolically with song and display, but some of them turn into real brawls.
Experiments with color-banded birds have shown that males return to their territories each year. In a typical marsh, opportunities for young males open up only as old males die. Redwings seem to recognize each other as individuals. Males who were neighbors last year tend to settle their disputes without actual combat. Fights are far more likely when new birds move into a territory.
All of this jockeying for position is preliminary to the arrival of the females. Female redwings don't look much like the males. Instead of glossy black and red, they are brown striped birds with a slight wash of pink on the breast that is visible only in a good light.
When the females arrive, we will see another reason scientists are interested in studying redwings. This is a polygynous species. Males on their territories will try to attract not just one female, but a whole harem. Not all of them will succeed at this. Some will get only one mate, and others will collect as many as four, but two is the most typical number.
For students of evolution, this arrangement raises all sorts of questions. Differences in reproductive success are regarded as the engines that make the process of natural selection work. Well-adapted creatures live long lives and have many offspring, thus passing their good genes on to large numbers in the next generation. Less-favored individuals are eaten by predators or driven out of the choicest territories or turned down flat when they try to get a date, so their genes perish with them.
So one of the questions for redwing students is who gets the girls? Do the biggest harems go to the biggest males or the most aggressive or the birds with the brightest epaulets or do they go to the males with the best territories?
The answer may be all of the above. Different scientists have seen different things and drawn different conclusions from what they saw. However, the preponderance of evidence is that females are more interested in the quality of the territory than in the quality of the male. A male whose territory offers good nesting sites will attract females regardless of his personal qualities.
The obvious counterargument to this conclusion would be that the best males get the best territories, but again, things are not that simple. With males showing such a strong tendency to spend their whole lives on the territories they established when they were young, the quality of a male's territory may depend more on what was available when the bird came of age than on his personal qualities. If he hits adulthood at just the right moment, he can move directly into the penthouse. Hit it at the wrong time, and he gets stuck in the slums all his life.
There is a further complication. Thanks to our intimate knowledge of the private lives of redwings we know that they mess around a lot. Consider this report from a biologist named Maurice Giltz who studied redwings in Ohio and who saw things that rendered him nearly incoherent: "On three occasions around four o'clock in early May, I observed bright pink to red-breasted females gather in a group increasing in size to 45 females as they flew over an alfalfa field of 40 acres. These females flew to an adjacent old field beside a woodlot with brush and last year's growth of weeds emerging from puddles of water up to 80 square yards in size. The males in the area followed the females to the puddles and bathed with the females. There were alternating bathing and copulating of the whole group of birds, the males jumping from one female to another and all of them alternating in and out of the water. I concluded that promiscuity was rampant."
In another study in Colorado several male territory holders were subjected to the avian equivalent of a vasectomy. They copulated with the females of their harems, but their sterility prevented them from actually fathering any young. Despite that sterility, the females somehow laid fertile eggs and hatched baby redwings from them. Makes you wonder what ever happened to family values.
Most of the recent students of redwing behavior have been looking for evidence of sexual selection in operation. The concept of sexual selection goes back to Darwin, and it has been used to explain everything from the peacock's tail to the fat-padded mammaries of human females. The idea is that over many generations, peahens consistently chose males with the most gorgeous tail display and men consistently chose women with large breasts. The consistency of this preference then spread these traits through the entire population.
After many thousands of hours of careful observation, the question of whether, or how, sexual selection is operating in redwings is still wide open. Seemingly solid conclusions are regularly overturned by new evidence. Yesterday's promising hypothesis falls apart when put to the test, and a resounding maybe seems to be the answer to every question.
Perhaps we just know too much to be comfortable with broad generalizations. Perhaps we are encountering the full range of behavioral possibility in this widespread and numerous species. We don't expect all humans to act alike; perhaps we need a similar open-mindedness to study the actions of simpleminded species like the redwing.