In the summer, the air around California’s Central Valley rivers and streams is lively with birds flapping and chirping. Although these riparian areas go quiet in the winter, it’s not true that the birds are gone.
It turns out that while many birds headed south for the winter to tropical habitats, birds that breed in the boreal forest of Canada flew in to take their place. These “neotemperate migrants,” as the researchers call them, include birds such as the yellow-rumped warbler, white-crowned sparrow, fox sparrow, cedar waxwing, and varied thrush.
The new study highlights the need to protect and restore riparian habitats to support birds throughout their annual life cycle—not just during the breeding times of spring and summer.
Often neglected in conservation planning, wintering habitat can be key to a songbird’s survival, affecting its reproductive success, migration timing, and overall health.
“Habitat conservation and restoration doesn’t just benefit breeding birds, but also supports continental populations of boreal breeding songbirds that require winter habitat for the half of their life spent not on breeding grounds,” says coauthor Andrew Engilis, a scientist and curator of the University of California, Davis Museum of Wildlife and Fish Biology.
“We are sure that if similar analyses were done in other regions of the US, there would be similar results.”
The researchers examined bird diversity in the lower Cosumnes River and lower Putah Creek watersheds in the Central Valley between 2004 and 2012. They found that just as many bird species used the riparian habitats in the winter as in the summer, and genetic diversity was actually higher in the winter than during summer months.
“You might have to look harder, but there are just as many species there,” says lead author Kristen Dybala, a postdoctoral student at UC Davis at the time of the study and currently a research ecologist with Point Blue Conservation Science.
“We found strong evidence that Central Valley ecosystems are very important in supporting bird populations throughout the year.”
The study appears in The Condor: Ornithological Applications.
The Solano County Water Agency, Putah Creek Council, CALFED Bay-Delta Program, US Environmental Protection Agency, California Department of Water Resources, UC Davis Department of Wildlife, Fish and Conservation Biology, and the cities of Davis and Winters, California, supported the work.