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Study of Songbirds’ Calls Provides Important Climate Insight

Study of Songbirds’ Calls Provides Important Climate Insight

An audio recording device in a semi-clear, plastic container on dark brown ground
The automated recorder model the scientists used. (CDFW photo by Brett Furnas)

Two avian researchers recently completed a groundbreaking study on the effects of climate change, based on the calls of California’s songbirds. By recording the sounds made by eight different songbird species, and tracking the dates they are most vocal and how frequently they sing, the scientists were able to develop a method to measure how the birds are adjusting to climate change.

CDFW Wildlife Ecologist Dr. Brett Furnas and William Jessup University’s Professor Michael McGrann analyzed data from two bird surveys, one done by CDFW and another led by William Jessup University, in the Klamath Mountains and Southern Cascades of northern California. Both studies used automated recorders to monitor bird sounds between 2009 and 2011. The results of their analysis, detailed in a research article entitled Using Occupancy Modeling to Monitor Dates of Peak Vocal Activity for Passerines in California, were published this month in a peer-reviewed, international journal of ornithology, The Condor: Ornithological Applications.

Furnas and McGrann’s study was prompted by the scientists’ concern that climate change could throw bird’s reproduction cycles out of sync with the seasons. Their work, which represents the first comprehensive assessment of songbird occupancy over approximately 15,000 square miles in California, earned high praise from Steve Beissinger, an expert on avian phenology at the University of California, Berkeley.

“Furnas and McGrann provide a textbook example of how to detect differences in the timing of nesting among bird species using information on the peak date of singing derived from surveys and automated recorders,” Beissinger said. “Their results support recent findings of a five-to-twelve day shift forward in the timing of peak singing by California birds in the nearby Sierra Nevada and coastal ranges in response to climate change.”

Because birds’ songs are correlated with their breeding behavior and are easily identifiable to species, the scientists found them to be a useful tool to provide new baseline data for the birds of northern California. Working together, they identified the precise dates of peak vocal activity for eight songbird species: Hutton’s vireo, hermit thrush, dark-eyed junco, Nashville warbler, MacGillivray’s warbler, yellow warbler, western tanager and black-headed grosbeak. In addition to gathering baseline data, Furnas and McGrann developed a method to track advances in the timing of vocal activity in the coming decades.

Male songbirds sing for several reasons -- including to advertise their territory or to find a mate with which to breed. When birds are at their most vocal, they are usually near the height of their breeding season, Furnas explained.

Much like the call of the imperiled “canary in the coal mine,” changes in the frequency or timing of these native birdsongs can serve as barometers of the cumulative impact of climate change.

“When the canary starts singing you know that there is a danger, such as a buildup of dangerous gasses in a mine,” Furnas explained. “When the birds in our study start singing earlier in the season, they are warning us that climate change is starting to disrupt complex ecological cycles that developed slowly over millions of years of evolution.”

One of the most interesting findings of the study so far is a hint in the baseline data that migratory birds may be at greater risk than non-migratory birds. “We found the highest singing activity for migrant birds spanned a shorter number of days than the highest singing activity for non-migratory birds,” Furnas said. “This could be because migratory birds have less flexibility to shift the timing of their breeding cycle. If they are prompted by increasing temperatures to migrate earlier in the year, they may arrive at their breeding grounds to find they don’t have enough insects to eat.

“Migratory birds have to compress a lot of activities into a shorter time period with less margin for error,” Furnas explained. “Think of it like scheduling a short holiday somewhere nice, but when you show up, bad weather cancels out a lot of your itinerary.”

This, in turn, negatively affects the very biodiversity that CDFW is responsible for monitoring.

“If all the species adjusted their ecologies similarly, perhaps that would be OK, but unfortunately, we expect that different insects and birds will react in different ways leading to a mismatch of conditions,” Furnas said.

Both CDFW and William Jessup University plan to continue bird surveys over the long term so that California has the information to support effective management of climate change and other conservation challenges.

Top photo: Singing hermit warbler, one of the species addressed in the study. (CDFW photo by Michael McGrann)


Science Spotlight: Studying a “Foundation Species” in the Shadow of Mount Shasta

Science Spotlight: Studying a “Foundation Species” in the Shadow of Mount Shasta

a white-spotted fawn lies in straw as its leg is measured
CDFW Environmental Scientist Brian Ehler measures the hind-foot length on a fawn captured near Medicine Lake for a mule deer study.

four deer are suspended in the air, in safety harnesses, from a red helicopter
CDFW Environmental Scientist Brian Ehler measures the hind-foot length on a fawn captured near Medicine Lake for a mule deer study.

Driving up Interstate 5 through Siskiyou County in northern California, one cannot help but take notice of the looming, majestic land mass of Mount Shasta, the largest volcano in the Cascade system.

In this rugged region of the Golden State, mule deer are an iconic species, valued by recreationists and required by wild carnivores who prey upon them for nourishment. Mule deer are considered a “foundation species” because the large landscapes that are necessary for their survival can also be home to a vast array of other wildlife and plant species. But mule deer populations have dramatically declined in recent decades across many western ranges, and in Siskiyou County, this decrease has prompted researchers from CDFW and the University of California, Santa Cruz to partner on a multi-year effort to investigate the population dynamics of this high-profile species.

Since 2015, 51 adult female mule deer and 37 fawns have been captured in the Mount Shasta region. Biological samples, including blood and parasites, have been collected, physical measurements of body condition and age recorded and telemetry collars attached to each subject. Collars on adult deer provide a GPS location every hour and alert researchers when a mortality occurs. The collars also document movement details, including migration routes and the location of critical winter and reproductive ranges. The fawn collars feature location beacons that allow researchers to monitor both general movements and when a mortality has occurred. Once a mortality alert is sent from a collar, a search of the site and an examination of the carcass ensues to determine if the deer died from predation or other causes, such as disease or malnutrition. The collars have timed releases and are set to drop off the animal after 18 months. Researchers can then reuse the collars after retrieving them by following a GPS signal. This high-tech, high-resolution documentation of deer behavior is vital for prioritizing the conservation value of landscapes so they may be better protected in the future.

With the recent arrival of gray wolves to northeastern California, predators are a key focus of the mule deer project. Understanding the influence this large canid will have on natural prey species begins with establishing baselines of how current predators -- including mountain lions, bears, bobcats and coyotes -- are affecting prey in this region. Mountain lions, which rely on deer as the primary component of their diet, are a major focus of this study. Researchers have captured and affixed five adult mountain lions with GPS telemetry collars, allowing them to track and study rates of predation, feeding patterns and diet composition.

The analysis of fecal DNA combined with new statistical techniques is another way to study population density and composition across broad landscapes. DNA analysis allows researchers to determine the sex and identity of an individual deer, which is used to estimate densities and gender ratios. Researchers are collecting fecal samples throughout the mule deer’s summer range, in the hopes of reliably extrapolating estimates of density and sex ratios across the entire region.

This project, which began in 2015, is scheduled to continue into 2019, as researchers strive to gain further insight into the lives of mule deer and predators across this ecologically complex and breathtakingly beautiful region of the state.

California Department of Fish and Wildlife photos.
Top photo: Mount Shasta in winter.



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