Pied-billed grebe by Tim Manolis
Hot off the press, Sacramento County Breeding Birds: A Tale of Two Atlases and Three Decades of Change raises red flags for some of the county’s wetland species.
Breeding bird atlases use field observations to record possible, probable, or confirmed nesting in uniform-sized blocks within a county or state. Biologist/artist Tim Manolis led a Sacramento County atlas project in 1988-93, but the results were never published. When Edward Pandolfino of Western Field Ornithologists heard about it he suggested repeating the effort and packaging the two data sets together. The second Sacramento atlas
, covering 2016-20, followed the lead of recent state atlases in the eastern US in using data uploaded to the birding app eBird to supplement targeted observations. “It’s a lot more efficient, and lets everybody get involved,” says Pandolfino, lead author of the publication.
Overall avian species richness didn’t change significantly, but distributions did for many species. Some wetland specialists, including cinnamon teal, pied-billed grebe, common gallinule, American coot, northern harrier, and yellow-headed blackbird, were found in fewer blocks. Pandolfino notes that the grebe, gallinule, and coot, which have similar breeding requirements, disappeared from almost the same blocks. “Some of these blocks had no net loss in hectares of wetlands but a dramatic increase in development,” he adds. “You wind up with patches surrounded by development where the birds are vulnerable to predators.” Rice field acreage in the Natomas Basin, which hosted black terns and American bitterns, was reduced by residential development and airport expansion; the tern no longer nests in the county. Trends are less clear for other species, like herons and egrets. On the positive side, raptors once hammered by DDT have rebounded, and Cooper’s hawks, western bluebirds, and others have adapted to urban areas.
Pandolfino cautions that atlases show presence, not numbers. “The data is binary—yes or no for each block,” he says. “A species may be declining in population but still breeding in the same block.” But that doesn’t reduce the value of the project as a baseline.