SAN FRANCISCO, Nov. 13 (Xinhua) -- Many of birds in the western U.S.state of California are breeding five to 12 days earlier than they did 75 to 100 years ago, a new study led by a University of California Berkeley (UC Berkeley) researcher showed Monday.
The study, to be published online for the Nov. 13 week by the journal Proceedings of the National Academy of Sciences, compared nesting data from the early 1900s to similar data today and found that California birds are nesting earlier to avoid warmer weather.
More than 200 species of California birds were examined for their overall nesting behaviors in the study led by former UC Berkeley graduate student Morgan Tingley, now an assistant professor at the University of Connecticut in Storrs.
Past research found that not all California birds in mountains would be migrating north or to higher elevations for cooler temperatures as a result of global warming.
In the past decades, higher temperatures have prompted early arrivals of spring, a phenomenon long observed by the general public, which resulted in plant leaves and seeds growing earlier and insects emerging earlier.
The leaves, seeds and insects are an important source of birds' food, which would affect the birds' pattern of nesting.
The latest study, a UC Berkeley press release Monday said, highlighted an interesting discovery. While nesting one week earlier, birds produce eggs at a temperature about 1 degree Celsius lower if they do at the normal time in the same place.
"By nesting a week or 10 days earlier, birds are avoiding some of the negative effects of climate warming," Professor Steven Beissinger was quoted by the press release as saying.
Beissinger, also a co-author of the study, is a UC Berkeley professor of environmental sciences, policy and management.