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Spring is the perfect time for songbird breeding in California’s Central Valley: neither too hot nor too humid. But climate change models indicate the region will experience more rainfall during the breeding season and days of extreme heat are expected to increase. Both of these changes threaten the reproductive success of songbirds, according to a study from the University of California, Davis.
The study, published on January 16 in the journal Biological preservationdetails the impact of extreme heat and rainfall on songbirds along the Putah Creek Nestbox Road in Yolo County.
Although centered on the Central Valley, the study serves as a warning for other Mediterranean ecosystems.
“The changes that are happening in California’s Central Valley – increasing temperatures, wetter springs, greater variability – these impacts are happening in Mediterranean landscapes,” said lead author Jason Riggio, postdoctoral researcher at the Museum of Nature. Fauna and Fish Biology from UC Davis. “In spaces where birds already live in a wildly variable climate, small changes will make a big difference.”
The study also shows that some birds adapt to modified systems. For example, Western Bluebirds and Tree Swallows have as much breeding success in orchards near Putah Creek as they do in their natural habitat. For these species, orchards are not the ecological traps that researchers initially expected. Other species prefer to build their habitats in the riparian habitats of forests and grasslands.
A Ashy-throated Flycatcher on banding day. Intern students treat their nestmates in the background. UC Davis Russell Ranch, June 2016. Photo by Evelien de Greef
Data nest boxes
Climate models predict that regional rainfall should decrease from October-January and increase from February-April, which would bring about the bird breeding season. Additionally, an estimated 5.4 degrees Fahrenheit (3 degrees Celsius) increase in average maximum temperature by 2100 will challenge species already at their temperature limits.
To study the impacts of these changes on songbirds, the researchers analyzed 11 years of data collected by Nestbox Highway project staff and their group of undergraduate interns from the UC Davis Museum of Fish and Wildlife. This included 2,305 nesting attempts and more than 7,100 nestlings among four species of cavity-nesting songbirds: western bluebird, house wren, tree swallow and ash-throated flycatcher.
They found that the birds’ physical condition decreased due to rainfall or extreme temperatures. Wetter nesting periods reduced reproductive success and nest weight in wrens, swallows and bluebirds. Higher temperatures during the breeding season also resulted in lower breeding success and nest weight for all four species.
“Based on these results, it appears that the effects of climate change in the Central Valley of California – and in Mediterranean systems globally – are likely to have significant and primarily negative impacts on songbird reproduction. nesting in cavities,” Riggio said.
He adds that there are still pockets of songbirds that are doing well in both natural and modified habitats, and that protecting remaining habitat fragments can benefit species facing environmental change.
Build a box, bring back a bird
Day-old tree swallow chicks snuggled up in their feathery nest. Near Winters, CA, May 2020. Photo by Hanika Cook, UC Davis
Study co-author Melanie Truan, an ecologist researcher at the UC Davis Museum of Fish Biology and Wildlife, started the Nestbox Highway in 2000 as a graduate student with the goal of bringing back the songbirds at Putah Creek.
Many native cavity-nesting songbirds had lost their nesting opportunities as non-native birds increased and the large trees with the holes they preferred were replaced by agricultural and other land uses. Western Bluebirds, once abundant in the area, had become virtually non-existent in the area.
A hundred nest boxes were installed in the first year, attracting, among others, a family of bluebirds. Today, more than 200 boxes attract hundreds of bluebirds and several other bird species to Putah Creek and the surrounding area. Staff and undergraduate trainees tick boxes weekly to record the progress of nesting attempts, eggs and nestlings. Before fledging, all chicks are measured and banded.
“The Nestbox Highway project is the most inspiring and encouraging part of what I do,” Truan said. “I’m so happy that this project that started as a conservation and education project to see what’s going on is turning into something that can provide data for research.”
The study also highlights the importance of long-term data sets to help understand the impacts of climate change and land use on birds and other species.
Additional study co-authors include Andrew Engilis Jr., Hanika Cook, Evelien de Greef, and Daniel Karp of UC Davis.
The study was funded by the Solano County Water Agency. This would not have been possible without the support of participating landowners and land managers, as well as the interns and staff of the UC Davis Museum of Wildlife and Fish Biology.
Thanks to UC-Davis for providing this news.