What's the answer? To train a vast network of citizen scientists, who can gather data at a speed and volume that's unprecedented in scientific research, providing rapid preliminary assessments of the status of threatened bird species. In some ways, the establishment of this network--ready to go whenever data on threatened birds are needed quickly--is more important than the individual Lab projects that spawned it. Project Tanager and its successor, Birds in Forested Landscapes, have added huge amounts of new data on woodland birds, but they also served as a vital training ground for our volunteer researchers--all of whom had to go beyond their knowledge of birds and learn how to identify plants, habitat types, and other environmental factors. Many participants have written to say how much the projects helped to make them more well-rounded as naturalists. They also learned about the methods of science. Now the basic infrastructure is in place that will enable Lab researchers, through the project participants' network, to gather data on threatened species in the shortest possible time.

A case in point--which shows the potential value of citizen science efforts--is the Lab's research on the Cerulean Warbler, a bird whose population has dropped by 3.2 percent per year in the East since 1966 and is a possible candidate for federal listing as an endangered species. This species may be expanding its range and increasing in numbers in New York, New Jersey, and the New England states; however, in these areas, Cerulean Warblers are not adequately censused by the Breeding Bird Survey. How can we make accurate estimates of this species' population trends or even begin to make habitat management recommendations without learning more about the Cerulean Warbler's specific habitat requirements and regional population densities? Why is it, for example, that several dozen Cerulean Warbler pairs nest in a cluster along Salmon Creek (not far from the Lab of Ornithology), while a kilometer or two up the creek there are apparently none--even though the habitat looks similar?

To gather data quickly from a large number of study areas, the Lab developed the Cerulean Warbler Atlas Project (CEWAP), which is now linking volunteer birders and professional biologists in an attempt to survey and map all known breeding populations of this beautiful, sky-blue songbird (see Birdscope, Winter 1998). We started small last year, focusing our attention only on the Northeast, but this year Lab volunteers are conducting surveys throughout the Cerulean Warbler's breeding range. To amass this much data over such a wide area using professional scientists would take years, if not decades. But we plan to complete the data-gathering phase of this project in only two breeding seasons.

How has the project done so far? In its first season, CEWAP volunteers surveyed approximately 120 sites and found roughly 1,000 male Cerulean Warblers--the largest numbers being in New York and West Virginia, where the most intensive surveys took place. But we also had good coverage in New England and, interestingly, the 13 Cerulean Warblers found in Massachusetts topped the entire previous population estimate for the species in that state. Unfortunately, we had the fewest northeastern CEWAP participants in Pennsylvania--in the heart of the Cerulean Warbler's range.

Lab researchers entered the locations where CEWAP participants saw Cerulean Warblers into a Geographic Information System (GIS). CEWAP participants found significant populations of Cerulean Warblers in Upstate New York, northern New Jersey, and several areas in West Virginia. In addition, we learned about a large population in nearby Ontario, Canada, in an area being studied by Raleigh Robertson and his students at Queens University.

Our 1997 survey data revealed that Cerulean Warblers live in a much wider range of habitats than researchers generally believed. As we reported in the Winter 1998 issue of Birdscope, our participants found the greatest number of these birds either in bottomland forests or on dry ridges. When we divided the sites geographically, we found that the majority of occupied sites in the New York-New England region were in bottomland forest, whereas the vast majority of sites farther south in the Appalachian region were on dry ridge tops (see graph below).

This graph illustrates the use of upland versus bottomland forest habitats by Cerulean Warblers in the northeastern United States (number of birds found in parentheses). In New York and New England, more Cerulean Warblers were found at bottomland sites, whereas in the Appalachian region, more occupied sites were in upland habitats.

So, what is the common denominator between the two different types of habitat that Cerulean Warblers find attractive? That very question was a primary theme at a symposium on Cerulean Warbler biology that took place this past April at the North American Ornithological Conference in St. Louis, Missouri. Lab biologists Ken Rosenberg and Sara Barker presented a paper there on the habitat use and population status of Cerulean Warblers in the Northeast--based entirely on data collected by CEWAP volunteers. Researchers at the symposium noted that occupied Cerulean Warbler sites usually have tall trees protruding above the canopy. Both riparian forests and ridge tops create a situation in which individual tall trees can tower above the rest of the forest, providing a singing warbler with an extensive view of its own and adjacent territories. In much of the Cerulean Warbler's range, large oak trees were important components of the birds' habitat--indeed, the presence of tall oaks was frequently mentioned by CEWAP participants as the factor that distinguished sites with Cerulean Warblers from similar forest areas nearby that lacked the birds. If our CEWAP data from the current field season continue to back up that finding, this could be an important piece of information in determining the specific conservation needs of the Cerulean Warbler, providing a more fine-tuned description of the kind of habitat that should be preserved to help the species.