Projects to map the distribution of breeding bird species in a given area have covered numerous California counties. Called breeding bird atlases, they describe abundance, timing of breeding, and aspects of life histories. Trained citizen scientists do the field work. Their observations are synthesized into species accounts and maps, which reveal a great deal about the lives of local birds. It also helps inform conservation and management decisions.
Three neighboring counties, Sacramento, Solano and Napa, have completed atlases. I recently perused the atlases for Solano and Napa. They offer insights into Yolo County’s breeding birds, including (1) possible sources of Yolo breeders; (2) region-wide range contractions; and (3) region-wide range expansions. Let’s look at those.
Species that breed regularly near the Yolo border could be sources of occasional or suspected breeding birds in Yolo, and should be looked for more carefully here. Several species are confirmed breeders just over the Napa County line east of Lake Berryessa, including Cassin’s vireo, dark-eyed junco and Lawrence’s goldfinch, while Wilson’s warbler and chipping sparrow are probable breeders there. Cassin’s vireo is also a possible breeder in Cold Canyon in Solano. The vireo has nested on the Blue Ridge in Yolo County. Common merganser probably breeds near Lake Berryessa in Napa County, and this may explain the occasional summering bird in Putah Canyon. Purple finch nests in the Wragg Canyon area near Lake Berryessa. Finally, the main tributary of Cold Canyon in Solano County, Wild Horse Canyon, has many coastal forest birds, including chestnut-backed chickadee and Steller’s jay. It could be a source for the sporadic occurrence of these species in Putah Canyon.
Several range contractions match those in Yolo. Prairie falcon seems to have disappeared as a breeder in Yolo. Likewise, there has been only one nest of prairie falcon in Napa in recent decades, and the species is now absent from Solano. Purple martins nest only in the western mountains of Napa County, nowhere close to Yolo, and there are none in Solano. This species used to nest in our western hills. Yellow warbler was widespread in Napa into the 1980’s, but was gone by 2010 and has been absent from Solano in recent decades. It went missing from Yolo years ago.
Several species have expanded eastward from the coastal forest into our area. Chestnut-backed chickadee expanded into Solano in the mid-twentieth century, and was confirmed as breeding recently. Allen’s hummingbird has reached Vacaville and Rio Vista, though not (yet) Yolo. Pileated woodpecker is a recent immigrant to the east slope of the Vaca Mountains in Solano, and perhaps thence to Putah Creek. Pygmy owl was in western Napa, but not Solano or Yolo, before the late twentieth century. Brown Creeper expanded eastward to breed at Lake Solano County Park in 2011. There are recent records from Yolo. Breeding juncos are recent arrivals in Solano, are probable along Putah Creek, and nested in Yolo this year.
Yolo Audubon began an atlas project in 2008. It remains incomplete, and would need a large, committed band of volunteers to finish it.
Visit the website of the Napa Solano Audubon Society for information about its breeding bird atlases, at the Citizen Science tab.
Michael Perrone, Conservation Chair, YAS