Some Breeding Songbirds Face a Mismatch as a Result of Climate Change

Spring in California's Central Valley is ideal for breeding songbirds because it is not too hot or too wet.

However, climate change models predict that the region will receive more rainfall during the breeding season, and days of extreme heat will increase.

According to a study from the University of California, Davis, both changes endanger songbird reproductive success.

Climate change presents a mismatch for songbirds' breeding season

(Photo : JOSEPH EID/AFP via Getty Images)

The study, which was published in the journal Biological Conservation on January 16th, details how extreme heat and rainfall patterns have impacted songbirds along the Putah Creek Nestbox Highway in Yolo County.

While the study focuses on the Central Valley, it serves as a warning for other Mediterranean ecosystems.

"The changes occurring in California's Central Valley - rising temperatures, wetter springs, increased variability - these impacts are occurring across Mediterranean landscapes," said lead author Jason Riggio, a postdoctoral scholar at the UC Davis Museum of Wildlife and Fish Biology.

In areas where birds already face extreme climate variability, small changes will make a big difference.

The study also showed that some birds adapt to altered systems.

Western bluebirds and tree swallows, for example, are having as much reproductive success in orchards near Putah Creek as they do in their natural habitat.

The orchards are not the ecological traps that researchers predicted they would be for these species.

Other species prefer riparian forests and grassland habitats for their homes.

Climate models predict that regional precipitation will decrease from October to January and increase from February to April, extending the breeding season for birds.

 Furthermore, an estimated 5.4 degrees Fahrenheit (3 degrees Celsius) increase in average maximum temperature by 2100 will put species that are already at their temperature limits under strain.

The researchers analyzed 11 years of data collected by Nestbox Highway project staff and its cadre of undergraduate interns from the UC Davis Museum of Fish and Wildlife to study the effects of these changes on songbirds.

This included 2,305 nesting attempts and over 7,100 nestlings from four cavity-nesting songbird species, including western bluebirds, house wrens, tree swallows, and ash-throated flycatchers.

Melanie Truan, a research ecologist with the UC Davis Museum of Wildlife and Fish Biology, started the Nestbox Highway as a graduate student in 2000 in an effort to reintroduce songbirds to Putah Creek.

Many native cavity-nesting songbirds have lost nesting opportunities as the number of non-native birds has increased and large trees with the holes they prefer have been replaced by agricultural and other land uses.

Western bluebirds, which were once common in the area, had become nearly extinct.

They discovered that bird fitness declined in the presence of extreme precipitation or temperature.

House wrens, tree swallows, and western bluebirds had lower reproductive success and nestling weight during wetter nesting periods.

Higher breeding season temperatures also resulted in lower reproductive success and nestling weight for all four species.

That first year, one hundred nest boxes were installed, attracting a family of bluebirds and other birds.

More than 200 boxes now attract hundreds of bluebirds and other bird species to Putah Creek and the surrounding area.

Weekly, staff and undergraduate interns inspect the boxes to track the progress of nesting attempts, eggs, and nestlings.

All nestlings are measured and banded before they fly.

According to Truan, the Nestbox Highway project is the most uplifting and encouraging aspect of his work.

Also Read: Songbird Population Decline Associated with Early Spring

How weather and climate affect songbirds

Weather, as we all know, changes from year to year, and climate is the long-term trend of weather patterns, as per the National Park Service.

Songbirds, like many other species, are affected by both short-term and long-term weather patterns.

But what are these effects, and how do they react?

The researchers used songbird counts (the abundance of passerines or perching birds) from 1995 to 2019 in Denali National Park and Preserve to assess how the previous year's weather impacted the current year and how climate has shifted bird locations in elevation over the last 20 years.

They discovered that weather and climate can exert complex and sometimes contradictory forces on songbirds and that not all songbird species respond in the same way.

For example, in songbirds that use shrub habitats, they discovered that their numbers increased in the year following a warm nesting season, but decreased over time and shifted upslope as shrubs shifted to higher elevations.

The temperature during the previous year's nesting period had the greatest short-term impact on the number of songbirds observed.

The amount of rain and snow, as well as the timing of snowmelt, influenced different songbird species in different ways, but researchers discovered that drier and earlier snowmelt resulted in greater songbird abundance.

Understanding how climate impacts songbird populations over time and on an annual basis will help experts understand the changes seen in subarctic songbirds.

Related article: This Tiny Traveling Songbird Crosses Entire Oceans Without Rest