Climate change presents a mismatch for the breeding season of songbirds

Spring is the sweet spot for breeding songbirds in California’s Central Valley – not too hot, not too wet. But climate change models indicate that the region will experience more rain during the breeding season, and days of extreme heat are expected to increase. Both changes threaten the reproductive success of songbirds, according to a study from the University of California, Davis.

The study, published January 16 in the journal Biological Conservationdetails how extreme heat and rain patterns have affected songbirds along the Putah Creek Nestbox Highway in Yolo County.

While 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 — rising temperatures, wetter springs, greater diversity — those effects are happening in Mediterranean landscapes,” said lead author Jason Riggio, a postdoctoral scholar. with UC Davis Museum of Wildlife and Fish Biology. “In spaces where birds are in extremely variable climates, small changes will make a big difference.”

The study also offers signs that some birds are adapting to altered systems. For example, Western Bluebirds and Tree Swallows find as much reproductive success in the vegetation near Putah Creek as in their natural habitat. For these species, vegetation is not the ecological traps that researchers first expected. Other species prefer to build their homes in riparian forest and grassland habitats.

Data nestboxes

Climate models predict that regional rainfall is expected to decrease from October-January and increase from February-April – driving the birds’ breeding season. Also, an estimated 5.4 degrees Fahrenheit (3 degrees Celsius) increase in average maximum temperatures by 2100 will challenge species at their temperature limits.

To study the effects of these changes on songbirds, researchers analyzed 11 years worth of data collected by Nestbox Highway project staff and a cadre of undergraduate interns from the UC Davis Museum of Fish and Wildlife. This included 2,305 nest attempts and more than 7,100 nestlings across four species of cavity-nesting songbirds – Western Bluebird, House Wren, Tree Swallow, and Ash-throated Flycatcher.

They found that the bird’s fitness decreased amid extreme rainfall or temperature. A wetter nesting season reduced reproductive success and nestling weight in wrens, swallows, and bluebirds. Higher temperatures during the breeding season also resulted in lower reproductive success and nestling weight for all four species.

“Taken together with these results, it appears that the effects of climate change in California’s Central Valley – and in Mediterranean systems around the world – are likely to have widespread and mostly negative effects on songbird nesting reproduction. in the cavity,” Riggio said.

He added that there are still pockets of songbirds that do well in both natural and modified habitats, and protecting the fragments of habitat that remain can benefit species coping with environmental changes.

Make a box, bring back a bird

Study co-author Melanie Truan, a research ecologist at the UC Davis Museum of Wildlife and Fish Biology, started Nestbox Highway in 2000 as a graduate student in an effort to restore songbirds to Putah Creek.

Many native cavity-nesting songbirds lost their nesting opportunities as non-native birds increased in number and as the large trees with holes they favored were replaced by agriculture and other land uses. Western Bluebirds, once abundant in the region, are almost non-existent in the area.

One hundred nest boxes were installed that first year, attracting a family of bluebirds, among other birds. Today, more than 200 boxes deliver hundreds of bluebirds—and several other bird species—to Putah Creek and the surrounding region. Staff and undergraduate interns check the boxes weekly to record the progress of nesting attempts, eggs, and nestlings. Before fledging, all nestlings are measured and banded.

“The Nestbox Highway project is the most inspiring and empowering part of what I do,” Truan said. “I’m glad this project that started as a let’s-see-what-happens conservation and education project is turning into something that can provide data for research.”

The study also highlights the importance of long-term data sets to help unravel the effects of climate change and land use on birds and other species.

Additional coauthors of the study 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, and the interns and staff of the UC Davis Museum of Wildlife and Fish Biology.

Thanks to UC-Davis for providing this news.