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Davis, California

Tuesday, April 23, 2024

Birds Bounce Back in Putah Creek


Habitat restoration improved populations of 27 out of 41 bird species since 1999

The Putah Creek Riparian Reserve has rebounded significantly over the last 20 years since the Putah Creek Accord restored water flow to the area. A team of wildlife biologists publishing in the journal Ecological Restoration have shown that bird populations have more than doubled in that timeframe, with insects, fish, turtles and river otters also returning to the recovering ecosystem. Kristen Dybala analyzed much of this collected data as a postdoctoral scholar in the UC Davis Department of Wildlife, Fish and Conservation Biology.

“We hoped that we would see some growth in the riparian species,” said Dybala, the first author of the paper, who now serves as a senior research ecologist at the conservation nonprofit Point Blue. “We wanted to know that the efforts on the creek have been providing the specific habitats for the riparian bird species.”

Members of the UC Davis Museum of Wildlife and Fish Biology have been collecting population data of more than 40 bird species along Putah Creek since 2000, when the annual flow to the creek was increased. The creek had suffered in the 1990s from droughts and low water levels, which caused population and wildlife loss. The creek’s flow was significantly altered by the creation in the 1950s of the Monticello Dam, which formed Lake Berryessa. Concerned citizens of Solano and Yolo Counties were able to force an agreement with the Solano County Water Agency to restore some flow from the dam to assist the native fishes.

To monitor how the creek was responding to cold water flowing into the ecosystem, 14 sites were chosen along nearly 25 miles of Putah Creek, from the outflow near Monticello Dam to where the creek spills in to the Yolo Bypass. Riparian birds, which flourish along the river, were counted along with woodland birds such as woodpeckers and synanthropic species such as crows, which live near human settlements.

“If you start at the upper part of the creek above Winters, the bird life there is influenced a lot by the surrounding landscape, lots of oak woodlands and chaparral in the upper canyon,” said Andrew Engilis, the curator of the UC Davis Museum of Wildlife and Fish Biology and one of the authors of the paper. “The bird life tends to be anchored by the woodland habitat. As you move down the creek toward Davis, you enter an agricultural landscape. The dynamics of the birds begin to change. By the time you get to the end of the creek, you get the more riparian-dependent species.”

To make accurate bird counts, staff and students ventured to the 14 sites along the creek and listened to the bird calls. Skilled bird watchers can identify birds by the notes in their songs, and the sight of a yellow warbler in a tree or an Anna’s hummingbird buzzing by the site serves as a visual confirmation.

“Some silent birds are too poorly seen to be identified and some notes heard cannot confidently be assigned to species,” said John Trochet, a research affiliate at the UC Davis Museum of Wildlife and Fish Biology and one of the authors of the paper, in an email interview. “But the repetition of the surveys in space and time leaves large, significant numbers of identified birds allowing for trend assessment.”

Nearly all the birds included in the study increased in population density between 1999 and 2012, including riparian, woodland and synanthropic species. Riparian birds weren’t the only species focused on during restoration efforts along the creek. Nest boxes were installed on trees in the reserve, creating homes for birds which use cavities in trees to nest and breed. Woodpeckers normally create these cavities when they are carving out holes in trees searching for food. The populations of birds which use cavities while nesting enormously improved during the study period. Multiple restoration efforts combined together created better outcomes.

“Restoration projects targeted both terrestrial and aquatic environments,” Trochet said. “Much of the creek below Monticello Dam is incised and confined by levees. In some places along the creek, however, the valley flats are set back enough to do some stream course modification. Logs were set in the stream to create deeper pools for anadromous fish (like chinook salmon) to hole up en route to spawning in the creek. A meandering stream course was engineered in a few places, better mimicking what the channel likely looked like before the dam was completed in the 1950s. Gravels were added in places as spawning beds, because with the dam in place, that was the end of natural migration of gravels from upstream of the dam site.”

Cold water from the dam creates habitat for California fish, which help keep the waterways healthy and lively. Fish serve as food for some species of birds, which then create nesting habitats for other types of birds. The complex ecosystem of the Putah Creek Riparian Reserve is improving because concerned citizens managed to turn the faucet back on almost 20 years ago.

“When you have more water in the habitat, you have changes in humidity, the vegetation gets affected and becomes lusher, insects become more plentiful, birds become more plentiful because the resources increase,” Engilis said. “It’s all related to the re-watering of the creek.”

Increasing water flow to the creek, installing nest boxes in trees, and improving the surrounding landscape of the Putah Creek Riparian Reserve has significantly strengthened the bird populations in the area. Future work will continue to ensure the whole ecosystem can thrive for years down the line. The Solano County Water Agency will be funding bird monitoring through the UC Davis Museum of Wildlife and Fish Biology until at least 2027.

“Ultimately, we want riparian bird populations in the Central Valley to be large enough that they’re going to be resilient and able to recover from the challenges in the future,” Dybala said. “We want riparian ecosystems throughout the valley that are capable of supporting these bird populations and other wildlife and ecosystems processes.”


Written by: George Ugartemendia — science@theaggie.org


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