Heron Pond, the northernmost cypress swamp in the United States, is in the Cache River watershed.
Floodplain forests and their associated wetlands are among the most productive, biologically diverse habitats in the world, but they are also some of the most threatened. During the past 150 years, the combined effects of logging, draining, and farming have altered and fragmented many bottomland forest ecosystems in North America. Scientists think that the fragmentation of bottomland forest habitat has contributed to declines in populations of songbirds because of habitat loss and potential increases in nest predation and brood parasitism. In recent years, researchers have recognized the importance of restoring and preserving bottomland forests, and efforts are now being made to acquire, restore, and maintain bottomland forest habitats.
The Cache River Wetlands Restoration Project, located in the southern tip of Illinois, is one of the largest habitat restoration projects in North America. The ultimate goal of the restoration project is to acquire, restore, and manage over 60,000 acres of land as bottomland forest within the Cache River watershed. The project is a joint venture involving the U.S. Fish and Wildlife Service, The Nature Conservancy, the Illinois Department of Natural Resources, and Ducks Unlimited. Presently over 32,000 acres of land have been acquired, much of which has been taken out of agriculture and planted with a mixture of bottomland tree species.
In 1993, we began studying the bird communities in the remnant bottomland forests of the Cache River watershed to determine the abundance and nesting success of the birds prior to restoration. Based on data from more than 400 census points and 3,000 nests, we found that species diversity and abundance of migratory songbirds increased and rates of nest predation decreased with increasing size (width) of tracts of bottomland forest. Brood parasitism by Brown-headed Cowbirds (Molothrus ater) was prevalent everywhere, but was lowest in the largest, most unfragmented areas. These results suggest the importance of expanding medium and larger tracts and consolidating existing smaller tracts of bottomland forest.
The Prothonotary Warbler (Protonotaria citrea) has been the focal species for studying how natural processes, such as hydrologic fluctuations, affect the function and value of habitat for songbirds. We now know that fluctuations of water levels (both rate and amount) influence nest predation, in turn affecting season-long productivity of birds breeding in bottomland forests. We are now studying how productivity is linked to the site fidelity of adult songbirds, to the dynamics of local populations, and to a particular habitat being a "source" or a "sink" for songbirds. With continued research we will determine whether or not adult birds adaptively return to source habitats and avoid sink habitats.
Heron Pond, the northernmost cypress swamp in the United States, is in
the Cache River watershed.
Research of tree species preferences by foraging insectivorous birds during the breeding season has led to the recommendation that heavy-seeded species (e.g., hickories that are slow to recolonize restored bottomland forests) and uncommon trees that are preferred by foraging birds (e.g., silver maple) be emphasized in reforestation plantings.
Research during the winter of 1999 in the Cache River watershed established the importance of bottomland forests for wintering birds. The diversity and abundance of birds during the winter are much greater in bottomland forests than in adjacent upland forests. Also, the bottomland forest may provide critical winter habitat for birds of conservation priority (e.g., Red-headed Woodpecker, Melanerpes erythrocephalus; Brown Creeper, Certhia familiaris; and Rusty Blackbird, Euphagus carolinus).
This research in the Cache River watershed will ultimately fill in gaps in our knowledge of bottomland forest ecosystems, and increase our ability to effectively and efficiently restore and manage bottomland forests. We will also be able to monitor the success of the restoration over time, and use our results to assist with other bottomland forest restoration efforts throughout the United States.
Jeffrey P. Hoover and Scott K. Robinson, Center for Wildlife Ecology
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