California birds are nesting earlier because of rising temperatures, UC Berkeley study finds

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Birds in California are nesting more than a week earlier than they did a century ago, according to a recent UC Berkeley study.

The study, which was published in the Proceedings of the National Academy of Sciences on Monday, compared nesting data collected in the early 1900s with current data on more than 200 species of birds found in California. Researchers found that birds are nesting about five to 12 days earlier than they did 75 to 100 years ago to avoid warmer temperatures.

“What we found was that by breeding one week earlier, the temperature that the eggs are exposed to has decreased by about one degree Centigrade, which is about as much as California has warmed over the last hundred years,” said Morgan Tingley, a former UC Berkeley graduate student and assistant professor of ecology and evolutionary biology at the University of Connecticut.

The study was co-authored by Tingley, former UC Berkeley postdoctoral fellow Pete Epanchin, UC Berkeley professor of ecology and conservation biology Steven Beissinger and University of Connecticut postdoctoral fellow Jacob Socolar.

According to Tingley, the birds were exposed to higher temperatures and higher precipitation, which disrupts the synchrony between the time their eggs hatch and the emergence of their food resources.

Tingley said some species in California have already been found to shift their nests to higher elevations to compensate for increasing temperatures. This new study, however, shows that birds might not just be shifting in space, but also in their phenology, which is the time that animals do certain things in their life cycle.

“It forces us to take a step back and think, ‘Wait a minute, birds actually have a wider variety of ways to respond to this temperature issue than we might have considered initially,’ ” Socolar said.

According to Beissinger, the study’s comparisons were possible because of historical data collected by UC Berkeley biologist Joseph Grinnell and his students in the 1910s and 1920s.

The research team used data from field journals preserved in UC Berkeley’s Museum of Vertebrate Zoology for baseline comparisons to evaluate how birds have changed their geographical locations and their daily habits.

The results of the study show the extent of temperature changes across the state and how it impacts wildlife.

“This study is important because of both the scale, the geographic scale, and the large number of species that are shown responding to climate change,” Beissinger said.

Tingley said his lab is currently beginning new work on how the seasonal timing of events responds to climate change.

Socolar said he hopes the study will allow researchers to predict how birds will respond as the climate continues to change.

The team is also continuing to resurvey birds across the state based on Grinnell’s data. Beissinger added that the team is looking at nesting data others have collected across North America.

“We’re hoping to be able to put together a statewide picture of the changes that have happened over the last century and use that to forecast changes for the future,” Beissinger said.

Contact Phil Zhang at [email protected] and follow him on Twitter at @philzhangDC.