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Field & Street



The Swainson's hawks that nest in Kane County may not have fledged any young this year. Bob Montgomery, who works for the Max McGraw Wildlife Foundation in Dundee, discovered one nest, but saw no evidence that the birds that occupied it had any success. He did see some additional adults in other parts of the county, so there could have been one or two nests he did not find. There have been reports in the past week from local birders of an immature Swainson's in Kane County, so one of those undiscovered nests could have been successful.

The range map for Swainson's hawk in Peterson's Field Guide to the Birds shows a contiguous breeding range for the species that extends as far east as central Iowa and southeastern Minnesota. A tiny dot on the map marks the small, disjunct population in northeastern Illinois. How they got here is a mystery. It may be that in presettlement times the range of the hawk extended this far east. Perhaps habitat changes on the land between Kane County and central Iowa extirpated all the birds that once lived in that region. Or perhaps some wandering migrants, blown off course by storm winds, ended up here and found a way to make a living hundreds of miles from their conspecifics. All we know for certain is that they have been in Kane County for the past 20 years.

We can certainly say that the Swainson's hawk has been rare in the state as far back as our records go. The first Illinois nest was discovered in 1875 in Richland County, which is one county west of the Indiana line and more or less straight east of Saint Louis. In 1900 another nest was found near Philo, which is a few miles southeast of Champaign.

Since then, the few records we have all come from the northern part of the state, almost all from a triangle with angles anchored in Rockford, De Kalb, and Elgin. The Kane County birds are the only known nesting population.

Swainson's hawks are one of the species in the genus Buteo, a group that also includes red-tailed, broad-winged, and red-shouldered hawks. Buteos are built like miniature eagles, with long, broad wings and tails. The Swainson's hawk is about the same size as a red-tail, but its wings are more slender and pointed and its tail somewhat longer and more slender. Soaring high in the air, it almost looks like a peregrine falcon.

It often hunts by flying low over the ground like a northern harrier. This is a good method for a bird that does not fly fast. The low flight enables it to surprise its prey --it suddenly looms over a mouse or ground squirrel and seizes it before the animal has time to react. It also hunts from perches, sitting in trees or on fence posts, watching its surroundings and waiting for something edible to show itself. And, as an animal of the nearly treeless Great Plains, it spends a lot of time on the ground, waiting and watching.

It requires open country to hunt over and trees to nest in. In presettlement Illinois it was certainly a bird of the oak savannas. In South Dakota you would expect to find it nesting in the trees along riverbanks and hunting the prairies nearby. In a pinch it will build a nest in an isolated tree, and there are a few recorded instances of nests built on the ground.

The habitat requirements I have outlined here are almost exactly the same as those of the red-tailed hawk. If you were a PhD candidate looking for a thesis topic, you might consider looking into the question of how these two species divide the territory in the vast regions where they both nest.

One difference between them is the food they eat. Red-tails eat an enormous variety of creatures, ranging in size and ferocity from voles up to house cats. Swainson's hawks tend to stick to small rodents like mice and ground squirrels, and they also eat a substantial number of insects like grasshoppers and crickets. They sometimes hunt while in the air, catching flying insects in their talons.

This time of year Swainson's hawks are gathering in large flocks all across their breeding range and beginning their migratory movement south for the winter. They make the longest migratory journey of any North American buteo, heading south through the tropics to winter on the pampas in Argentina, 15,000 miles or more from their nesting grounds.

Two months from now you could stand on a high ridge on the isthmus of Panama and watch almost the entire world population of Buteo swainsoni float by. They let the thermals carry them, soaring so high on the rising air they can't be seen from the ground and then gliding in a slow southward slide until they can pick up another thermal.

Not all Swainson's hawks make this arduous flight. A small population spends the winter on the grasslands of Florida. Bob Montgomery wonders where those Florida birds come from. He would like to be able to link breeding areas with wintering areas. It could be that our local birds, and other populations at the eastern edge of the species' range, make the short flight to Florida in the fall rather than the long flight to Argentina.

"If we could capture these birds and take some blood samples," he told me, "we might be able to find if they are genetically different from the western birds." Given the tiny Illinois population, such a program, or even a banding program, would not be worth the risk to the well-being of the birds, but it would be wonderful to know where the Florida birds spend the summer and where the Illinois birds spend the winter.

We also have reason to be concerned about the western population. The pampas are presently undergoing the sort of transition that hit the prairies of North America a century ago. The endless expanses of waving grass are being converted to deserts of wheat and corn, places where a hawk has a very hard time making a living.

Our tiny Kane County population gives the Swainson's hawk a place on the endangered species list in Illinois. You will often hear arguments against the idea that we need to protect a population like the Illinois Swainson's hawk. After all, this bird is apparently doing well over a contiguous range that extends from Alaska to northern Mexico and from Iowa to California. Does it really matter what happens to this isolated handful of birds that is somehow clinging to existence among the corn and soybeans of Kane County, Illinois?

It could. Maybe Montgomery's hunch that these birds are genetically different from the western birds is right. They may represent a distinct subspecies, and losing them could diminish the genetic pool of the species. Small, isolated populations are also likely sources of genetic innovation. A significant genetic change could zip through our Swainson's hawk population in no time. I am not saying this will happen, and nobody could say where such a change might lead, but it is generally a bad idea to restrict possibilities, to foreclose on the future.

The habitat of the Kane County birds is threatened by the continuing spread of the metropolis. The trees where they nest could be cut. The fields where they hunt could soon be covered with asphalt, concrete, and bluegrass. Can we protect these birds from such development? I checked with Deanna Glosser, endangered species program manager for the Illinois Department of Conservation, and found that the answer is maybe. It all depends on the nature of the threat.

The Illinois Endangered Species Protection Act requires state and local governments to consult with the IDOC about projects that could pose a threat to endangered species. The department can offer suggestions for changes in the project to reduce the threat or even state the opinion that the project should not proceed at all, but they cannot say no. Local governments, in some cases, have that power. If, for example, a developer wanted to subdivide land within the borders of a municipality, he would need the approval of the city government for his plans. They could deny him permission if they chose.

However, if a development did not involve subdividing, if, for example, a developer bought a single piece of land and put a single development--a shopping center, say--on it, he might not even have to ask the municipal authorities for permission.

So the IDOC can urge, recommend, and plead, but to a considerable extent our Swainson's hawks must depend on the consciences of real estate developers for their survival. Isn't that comforting?

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