For the past few weeks I've been spending as much time as I can afford studying the birds of the oak savannas of the midwest. This is a bookish enterprise. All but a few tiny, degraded remnants of our native savannas vanished before the end of the 19th century, so there is no place I can go to actually see a savanna and the birds that live in it.
So I'm looking at historical accounts written by people who were around when savannas still existed. And I'm studying the habits of various species of birds to figure out which ones have a way of life that would fit into one of the environments on a savanna. It's a matter of inference and surmise, of deductive reasoning from premises that are sometimes strong and sometimes not so strong.
My goal is to create a list of species we can call, with a fair degree of confidence, savanna birds. My deadline for the list is February 20. That is the day I have to give a talk on savanna birds at a conference on midwest oak savannas being held at Northeastern Illinois University and sponsored by the university, the Nature Conservancy, the EPA, and the University of Wisconsin at Stevens Point.
Ecology, like every other human endeavor, has its fashions, and right now the oak savanna, the mixture of grassland and trees that covered a large part of presettlement Illinois, is a fashionable ecosystem. It also represents a second stage in our rediscovery of the native vegetation of the midwest. You could say that stage one began about 60 years ago, when botanists at the University of Wisconsin started trying to create a native tall-grass prairie in the university's arboretum. It accelerated 30 years ago when Robert Betz of Northeastern Illinois University, working with Floyd Swink and Ray Shulenberg of the Morton Arboretum, began to study prairie remnants in the Chicago area.
Twenty years ago Betz persuaded the Nature Conservancy to buy the Gensberg-Markham Prairie, the largest remnant in the area, and his efforts had a lot to do with making public conservation agencies aware of the need to acquire prairie lands for preservation. Betz, Shulenberg, and Swink also played key roles in initiating the now-flourishing work of prairie restoration around Chicago. Some of that work helped arouse interest in the oak savanna.
Early accounts of the Illinois landscape all mention the groves of trees that were scattered around the prairie. Drawing on memories of Europe, travelers likened the land to the parks on English estates. The landscapes of our city parks are still nothing more than manicured savannas.
Early settlers were drawn to the oak groves on the prairie for sternly practical reasons as well as aesthetic appreciation. Groves provided shade on hot summer days, protection from winter winds, and wood for lumber and fuel. Downers Grove, Elk Grove, Buffalo Grove, and all the communities with the word "park" in their names are reminders of the attraction those oak groves exerted.
Ecologically, one of two things happened to the groves after settlers arrived. Where farmers turned their cattle loose in the groves, the old oaks remained as a canopy but the plants of the understory were nibbled to extinction. Where the groves became ungrazed woodlots, protection from fire allowed trees like the sugar maple and basswood to invade, converting the groves into dense forests. By the time botanists began the serious cataloging of native plant communities they couldn't find a good example of a savanna to survey.
We have learned a bit since then. A recently discovered plant list compiled in the 1840s has given us a small glimpse of some oak groves before much damage took place. And we have discovered a few remnants that escaped the notice of earlier investigators.
There is a temptation to focus on the oak groves when we think about savannas, since they seem like the most distinctive feature of the landscape. But the essence of a savanna is variation. There were indeed shady groves of tall oaks whose broad crowns formed a nearly continuous canopy of leaves. There were also large patches of prairie dotted with scattered single trees. There were groves that covered a single acre and groves that extended over hundreds of acres. There were groves of big old trees and groves of small young trees. And there were places called brush prairies where low shrubs of dogwood and blackberry and hawthorn were the dominant plants. Each of these varied landscape types would have had its own distinctive group of birds, so the list of savanna birds has to include them all.
Despite the lack of savannas to study and the complexity of the savanna landscape, I have found that it is possible to construct a list that is about 90 percent sure things and 10 percent species that reasonable people can disagree about.
The obvious candidates are birds whose ways of life require both trees and open areas. The red-tailed hawk is a good example, and so are robins and grackles, eastern bluebirds, and flickers. Red-tails nest in trees but soar high over open lands in their search for prey. Robins and grackles build their nests in trees but feed on the ground both under the trees and out in the open. Flickers and eastern bluebirds are both hole nesters, so they need trees, usually dead ones, for nest sites. Flickers are woodpeckers, but they often feed on the ground both in woods and in the open. Eastern bluebirds typically feed in open areas.
Robins and grackles are both perfect examples of savanna birds that have become birds of city parks, golf courses, and suburban neighborhoods. Flickers do well in those places too if the area is unkempt enough to have some dead trees--or at least dead branches--to provide nest holes. When farmers still used wooden fence posts, bluebirds commonly nested in them.
There is a whole group of species we usually think of as edge birds because we typically find them along the borders between woods and open ground. But most of these should really be thought of as brush birds. Song sparrows are a good example, along with yellow warblers and catbirds. In today's landscapes we typically find these birds at woodland edges, but that may be simply because woodland edges are a good place to find shrubs and brushy tangles. At Somme Woods, where I have been helping with a nesting survey for the past few years, we find these birds nesting in dogwood thickets well away from any trees.
There are other brush birds with a greater need for trees. House wrens need at least one dead tree to provide a nest hole, and indigo bunting males like to sing from the tops of the highest trees around. We can imagine them at edges where grove met prairie.
The greatest mysteries are the birds now on the endangered, threatened, or extirpated lists. Most creatures who qualify for the very dubious honor of inclusion on these lists are rare or extinct because their habitat has become rare or extinct. The Illinois lists are dominated by wetland species. Prairie birds are the next most numerous category. And then there are a number of species we would have to consider savanna species.
Bachman's sparrow is one of those. This is a southern bird whose range extended only as far north as the central part of our state. In Texas Bachman's sparrows live in pine groves. In the Georgia piedmont they live in brushy fields with young pines. Based on historical records and what few recent sightings we have, the Illinois birds prefer old fields with brush and scattered small trees. This was a savanna bird.
We used to have two kites in Illinois. Kites are a very aerial group of birds of prey. They feed on a mixture of large insects and small reptiles, amphibians, and mammals. They often snatch flying insects right out of the air and then eat them in flight, holding the luckless arthropod in one talon while pulling it apart with their beaks. The swallow-tailed kite, a bird that can take your breath away, has a wingspan of four feet and a deeply forked tail more than a foot long. You could imagine it living totally in the air, never touching ground at all. It is officially extirpated from Illinois. Its smaller relative, the Mississippi kite, is on the endangered list. These were savanna birds in Illinois. They nest in tall trees and hunt over both wooded areas and open prairies and marshes.
The long-eared owl is another likely savanna bird. This species also nests in trees and hunts over open areas.
As complicated as my job of historical construction is, I am supported by two thoughts. One is that despite the destruction of our native savannas, nearly all the birds that once inhabited it are still around. Their numbers and their geographic ranges may be much reduced, but they have not disappeared. Restoration efforts, combined with better management of lands where significant portions of savanna ecosystems remain, could bring them back.
My other comfort is that in the absence of healthy savanna ecosystems to study, no matter what birds I put on my savanna list, nobody can prove I'm wrong.