Illinois Natural History Survey - University of Illinois

Urban Conservation of a Wetland Bird Species

In spite of the loss of many of northeastern Illinois' presettle-ment wetlands, a large number of wetlands remain in this highly urbanized and rapidly developing region. These wetlands are home to significant populations of wetland birds. These include colonial species, such as Great Blue Herons, American Egrets, Double-crested Cormorants, Black Terns (Illinois endangered), and Black-crowned Night Herons (Illinois endangered), as well as species with dispersed distributions, such as Pied-billed Grebes (Illinois threatened), Common Moorhens (Illinois threatened), Least Bitterns (Illinois endangered), and Yellow-headed Blackbirds (Illinois endangered). A major impediment to the conservation of these species and their wetland habitat is a general lack of information regarding the population dynamics and habitat requirements of these species in urban environments. This paucity of information makes long-term planning for conservation, development, habitat mitigation, and habitat restoration extremely difficult.

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A surburban development arising in a wetland landscape of northeastern Illinois, habitat to a number of endangered and threatened wetland bird species.

Our research is currently focused on one species, the Yellow-headed Blackbird. This species was an abundant resident in the southwestern Great Lakes region a century ago. Since that time, however, its population has declined precipitously and Yellow-headed Blackbirds currently persist in small numbers in only a few populations east of the Mississippi. One of the largest of these populations is in northeastern Illinois, in the marshes of Cook, Lake, and McHenry counties. However, these marshes are under constant development pressure, and the Illinois Yellow-headed Blackbird population has continued to decreased at an alarming rate over the past 20 years (approximately 8% per year; Illinois Department of Natural Resources data).

We have been studying the northeastern Illinois population of Yellow-headed Blackbirds for the past two years in order to identify factors contributing to its decline, document whether individuals from this population return to the area annually, describe the movements of individuals among the marshes of the region, and describe the population trend and age structure. Our long-range goal is to gather the information required to develop a conservation plan that will ensure the survival of the Yellow-headed Blackbird in northeastern Illinois and in the southern Great Lakes area.

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The Yellow-headed Blackbird (Xanthocephalus xanthocephalus).

To date we have marked over 200 individual birds, establishing that adults breeding in one year are very likely to return to the area to breed again. We also found that these birds can and do successfully breed in close proximity to human development, provided that their marsh habitat remains intact. In addition, we found that nesting and fledgling success over the two-year period was relatively high, suggesting that the population is producing enough young to remain stable.

So why is this population declining, and why has this population, isolated by hundreds of miles from the large western populations, persisted? A longer period of investigation will be required to answer these questions. Declines may be solely due to the loss of habitat, in which case protection of sufficient marsh habitat may be all that is required to ensure the persistence of the species in Illinois. On the other hand, large-scale demographic factors may be partially responsible for the decline. As is the case with many migratory songbirds, young produced in one location seldom return to breed in the same area. Because the Illinois population lies hundreds of miles from the center of the species' range, it is possible that young birds looking for a place to settle seldom find the area. Like humans in a small rural town, the young that are produced there tend to move to the larger (bird) population centers and the population dwindles for lack of new recruits.

Clearly, this species is capable of co-existing with humans in urban and suburban Illinois. We are continuing to monitor the population of eastern Yellow-headed Blackbirds of northeastern Illinois in the hope of understanding what will be required to safeguard the remnant of this species.

David A. Enstrom and Michael P. Ward, Center for Biodiversity; James Herkert, Illinois Endangered Species Protection Board

Charlie Warwick, editor



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