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Birds in Forested Landscapes
The question "How much forest does a forest bird need?" is almost as difficult to answer as "How much wood could a woodchuck chuck if a woodchuck could chuck wood?" Though the first question is very basic, it’s not so simple to answer, particularly when you’re considering multiple species in different geographic regions. To address this question and many others, the Cornell Lab of Ornithology, in cooperation with Partners in Flight, has designed a new citizen-science project called Birds in Forested Landscapes (BFL). The project was field-tested during the 1996 breeding season and will be open to volunteer birders throughout North America this year. As habitats such as forests, prairies, and wetlands are lost because of changing land uses, biologists must determine how much habitat is required to support viable populations of birds. This challenge would be easier to meet if we were sure that the sum of the parts always equaled the whole. In other words, do six 50-acre patches of forest serve the same ecological purpose as a contiguous 300-acre forested tract? And does the shape of the forest patch or the amount of edge associated with it influence which birds use it? Scientific evidence suggests that forest fragmentation (dividing large forest tracts into smaller pieces separated by nonforest habitat) is detrimental to some woodland bird species. Project Tanager, the predecessor to BFL, showed that nest predators such as jays, crows, chipmunks, and raccoons, and nest parasites such as Brown-headed Cowbirds are much more likely to be found in heavily fragmented forests. However, because tanagers build their nests high in trees where they are difficult to observe, Project Tanager biologists and participants had a hard time determining whether the rates of nest predation and parasitism were abnormally high in fragmented forests. BFL was conceived to solve this problem and to address other management and conservation issues surrounding forest birds. The initial goal of BFL is to determine how forest fragmentation and land use influence the presence and nesting success of seven species of North American forest thrushes—Wood Thrush, Veery, Swainson’s Thrush, Gray-cheeked Thrush, Varied Thrush, Hermit Thrush, and Bicknell’s Thrush—and two forest raptors: Cooper’s Hawk and Sharp-shinned Hawk. Because thrush nests are usually placed close to the ground and hawk nests are larger and more conspicuous than most songbird nests, these nests should be easier to find and monitor than tanager nests. The project was designed in such a way that additional species can be studied in subsequent years using the BFL model. As a group, thrushes form a conspicuous component of forest bird communities; at least one species is found in virtually every region of North America. This means that almost anyone who wants to take part in this project will have at least one species nearby to study. Moreover, thrushes have loud, distinctive vocalizations, making them amenable to study with a standardized tape-playback protocol, playing a recording of the target species and listening for a response. In addition, thrushes were selected as the major focus of BFL because all but one of the seven species are declining over significant portions of their range. For example, Breeding Bird Survey (BBS) data from the Biological Resources Division show that the Wood Thrush has declined throughout much of its range at a rate of at least two percent each year since 1966. The Veery has also declined significantly over its entire range, and the Swainson’s Thrush has declined significantly in the East. Although only a small portion of the range of the Bicknell’s Thrush is sampled by the BBS, this species has shown an annual rate of decline of nine percent since 1980 in the sampled region. The Varied Thrush, a species found in the mature forests of the Pacific Northwest, is particularly vulnerable to land-use changes. Only the Hermit Thrush, whose large range partially overlaps those of the other thrushes, shows an increasing population trend. Accipiters such as Cooper’s Hawks and Sharp-shinned Hawks are excellent indicator species for determining the health of a forest ecosystem, because they are high on the food chain and have large breeding territories. In addition, these raptors occur in nearly every U.S. state and Canadian province. Both are long-distance migrants that winter partly in the Neotropics, although many individuals spend the winter in the United States. Because of habitat loss and population declines, these hawks are considered species of special concern in different parts of their range. By determining management and conservation guidelines for top-level avian predators, BFL will ensure that adequate habitat is provided for a large number of other forest birds. In addition to contributing to our knowledge of thrushes and hawks, BFL will serve as a conduit for habitat management and conservation recommendations to the developers of Partners in Flight’s North American Bird Conservation Plan. Partners in Flight is an extensive coalition of biologists, land managers, and educators committed to identifying the habitat requirements of healthy bird populations and ensuring the long-term protection and management of bird habitat throughout the continent. This is a colossal job and would be nearly impossible without the assistance of thousands of volunteers throughout North America. So, how does BFL work? Once you sign up, you’ll receive a research kit, which includes complete instructions, reference materials, data forms, and cassette tapes or CDs for censusing forest birds. You will have a choice of censusing thrushes, hawks, or both groups of birds (the protocols for censusing and monitoring nests of thrushes and hawks will differ slightly). All BFL participants will select census points in forest patches of different sizes, then visit each point at least twice during the breeding season to search for thrushes, hawks, or both, to look for evidence of nesting, and to record certain characteristics of their study sites. On the first visit, they will look and listen for thrushes, hawks, Brown-headed Cowbirds, and predators and play a recording of the target species’ vocalizations. On the second visit (and on any subsequent visits), they will look for evidence that the birds are breeding. In the field, participants record all their observations on field data sheets. Later, at their home or office, they can transcribe the data to computer-readable data forms and mail them to the Lab of Ornithology. Lab biologists will then analyze the data and report the results to participants (through Birdscope), land managers, and developers of the North American Bird Conservation Plan. The results will also be published in scientific journals and popular magazines. Volunteers can sign up to participate in BFL either by using the accompanying coupon, sending e-mail to forest_birds@cornell.edu, or calling (607) 254-2440. If you have already mailed a BFL sign-up coupon to the Lab, you don’t need to send a second one. Birds in Forested Landscapes is an excellent project for birding groups, such as bird clubs and chapters of the National Audubon Society, and, student organizations, such as chapters of The Wildlife Society. By becoming part of the BFL team, you will further your knowledge of bird identification and avian ecology, participate in scientific research, and help protect forest birds and their habitat throughout North America. Birds in Forested Landscapes is funded by the National Fish and Wildlife Foundation and matching donations, so there’s no charge for participating in BFL during the 1997 field season. |
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