Climate change comes home to roost: California birds are nesting earlier

Hundreds of species of birds across California are nesting earlier in the year than they were a century ago because of rising global temperatures, according to a new study out of UC Berkeley.

Researchers gathered both historic and contemporary data on the nesting habits of 202 different types of birds from throughout the state. What they found was that as temperatures increased, the birds adjusted their nesting habits to begin earlier in the year, when it was cooler.

"What we're finding is across a broad set of birds here in California, species are breeding earlier than they ever have before," said Steve Beissinger, one of the study's authors. 

For birds, there's a Goldilocks zone for nesting success; too hot or too cold and offspring numbers decline. That's both because of the temperature and the impact that it has on the availability of food sources like flowers, insects and seeds.

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On average, the researchers saw the birds nest between 5 to 12 days earlier than they had in the early 1900s. Since then the global average temperature has increased by 1.8 degrees Fahrenheit according to the U.S. Global Change Research Program.

"The good news is that even though the climate's gotten warmer, the species are shifting and adjusting the timing of their nesting in relation to that climate warming. So, they're nesting earlier to stay at the same temperatures that they were nesting in 75 to 100 years ago," Beissinger said.

But, conservative climate models predict that we're on track to see an increase of 3.6 degrees Fahrenheit in the average global temperature by 2100.

"We don't know yet if this strategy of staying in the same place and breeding earlier will be a solution as the temperature starts to hit five, six or maybe seven degrees Fahrenheit warmer on average in California in 100 years than it is now," said Beissinger.

What this means for the success of species across California is unclear. If birds can no longer survive by changing when they breed, they might have to change where it happens. As a result, we could see a migration of species northward towards cooler climates. 

The study was published in the Proceedings of the National Academy of Sciences.