A mourning dove has been living on my block since we moved in in early February, often perching in a tree on the corner or doing its head-bobbing pigeon walk around the courtyard of our building searching for food. It--only another mourning dove can tell whether it is a he or a she--may have found a mate.
I was pleased to see it, because in our highly urban Edgewater neighborhood the only other birds around were the alien triumvirate: starlings, house sparrows, and pigeons. Our lonesome mourning dove was the sole representative of North America in either the flora or the fauna of our community. It was the only living thing here now that would have been here 200 years ago. I developed a rooting interest in its well-being, so I am happy to see it has found a companion.
Rigorous honesty forces me to admit that the pair I am seeing now may be birds that just arrived in the neighborhood. The bird I was seeing last month may have flown headlong into a window and squashed its skull like a grape. But I prefer to believe that this is the same bird, and since pairing up is a normal springtime phenomenon, I'll go on believing that one of the birds in this pair is our resident dove.
There are other mourning doves in the neighborhood. I even see them in the shadows along Sheridan Road, where the solid wall of high rises shows what a dynamic free enterprise system can do to a lakeshore.
Most mourning doves spend the winter in small flocks, which break into pairs in early spring. Long-term studies suggest that these pairs are permanent, that the birds stay together for life. Of course the mortality rate is very high--about 55 percent per year for adult birds--so a lifetime commitment for most individuals lasts no more than a year.
Yesterday I heard doves singing for the first time this spring. One singer was perched on a wire in the alley behind my apartment. It could have been the bird I have been seeing for the past month, but I can't assume that without being sexist. The resident bird could have been a female that has now been joined by a male. The other singer was a block west on Winthrop Avenue. It would be interesting to know how many pairs a highly urban neighborhood could support. I should probably take some early morning walks and count singing birds--at least those I can hear above the traffic.
The singing--the soft, mournful cooing that gave the bird its name--means that the birds are setting up territories, laying claim to a piece of land they hope will be big enough and rich enough to support a family.
Once they start nesting they will keep it up until September, raising as many as five broods. As far as I can discover, mourning doves raise more broods of young in a typical nesting season than any other North American bird. However, those broods are very small. Two is the usual number of eggs in each clutch. By comparison, robins nest two or three times a season, but the female typically lays five or six eggs in each clutch.
If the marital fidelity of mourning doves suggests support for family values, their child-rearing practices are a feminist's delight. The female builds the nest, which is a platform of interwoven sticks so flimsy that you can stand underneath it and actually see the eggs through gaps in the weave, but the male finds the sticks and brings them to her.
Once the eggs are laid incubation is divided precisely between the sexes, with the male sitting on the nest by day and the female at night. Once the young hatch, after about two weeks, both parents feed them for the next two weeks, the time it takes them to mature to the point that they can leave the nest.
Birds of the family columbidae, pigeons and doves, produce a highly nutritious substance called pigeon milk, which is used to feed the young until they are old enough to take solid food. The "milk" is produced in the crops of both males and females.
A bird's crop is an enlargement in the esophagus. In some birds it's just a slight swelling, in others it's a well-developed sac, and in pigeons and doves it's a two-chambered sac.
Many birds, especially insect eaters, don't have crops. They feed more or less continuously throughout the day, taking in lots of small meals that they can digest as they go. Most birds with crops get only occasional shots at a really big meal. Vultures, for example, may go days between carcasses. The crop allows them to take in a very large amount of aged steak and store it until their stomachs are ready to digest it.
Seed-eating birds use their crops in much the same way. If a turkey finds acorns littering the ground under a particular oak, it can really pig out, stuffing as much as a pound of nuts in its crop to be digested at leisure. Finches of the northern forests store seeds in their crops during the day and digest them at night, providing themselves with a continuous fuel source during cold winter nights.
But only pigeons and doves produce milk in their crops. During the breeding season the walls of the crops of both males and females thicken by as much as 20 times. The milk comes from cells that are continuously sloughed off the insides of the walls. It is a cheesy substance, rather like ricotta. About 25 percent of it is fat, and another 10 percent is protein. The blind, helpless chicks stick their heads down their parents' throats to suck up the milk, which is their sole food during the first ten days to two weeks of life. As they get older they begin to swallow partly digested seeds mixed with the milk. When they leave the nest they are ready for the nearly all seed diet of their parents.
Much of what we know about the details of the lives of mourning doves comes from research paid for by hunting licenses. In 31 states, including Illinois, doves are considered game birds. We have regular seasons and bag limits on them. They are fast and maneuverable fliers, and you would need to shoot very well to hit one--so you can see the attraction for the sportsperson. However, the average mourning dove weighs about four and a half ounces--feathers, feet, and all--so you would have to kill a lot of them to put together a dinner. Plucking and gutting a bird is a major effort, and it's hard to see much sense in doing all that work if all you get is a mouthful of meat.
Mourning doves are the most widespread of the 17 species of columbidae native to North America. Their nesting range covers the continent from Alaska to Panama and the islands of the Caribbean. They can get along in all sorts of habitats. The mourning doves in the Edgewater of 200 years ago would have been feeding across open dunes and nesting in pines and cedars, and you can find them now in mesquite in the southwest or in cottonwood windbreaks on the Great Plains. They like open ground to feed on and scattered trees to nest in, but in a pinch they can nest on the ground.
It is hard to write about mourning doves without mentioning the other pigeon that was around these parts 200 years ago. The passenger pigeon, America's most famous extinct bird, might have been the most common bird in eastern North America in 1795. It favored dense forests rather than open woods, but like the mourning dove it was a seedeater, a builder of flimsy nests, a fast and powerful flier, and a devoted parent.
The main difference between the two species was the way they bred. Mourning doves scatter their nests. Pairs quietly install themselves in the thin trees of a Chicago parkway, raising their young while very few humans even notice their presence.
Passenger pigeons nested in huge colonies. Thousands of pairs of birds would gather where the chestnut and beechnut and acorn crops were especially rich and
raise more thousands of young. In the North America of 200 years
ago this was an excellent strategy. It took the utmost advantage of local and temporary abundances of food, and it simply overwhelmed the local predators. Cooper's
hawks or raccoons, whose populations were held in check
by the much lower numbers of resident prey, could stuff themselves silly and still not make a dent in the passenger pigeon colonies.
Unfortunately the strategy could not withstand large numbers of men with shotguns who had boxcars standing by to haul away as many pigeon carcasses as their marksmanship could create. And it couldn't withstand the loss of habitat created by the greatest clear-cut in history. The sadness in the coo of the mourning dove reminds us that we have something to be sad about.