ShareThisOrnithologists -- scientists who study birds -- published two studies this week saying that an increase in climate change during the past 40 years may have led to the disappearance of hundreds of bird species nationally.
Up to a third of the California's 310 species of birds could be threatened if greenhouse gas emissions aren't limited, according to the California Audubon study.
Climate change is expected to have more dire effects on bird species native to southern California than anywhere else in the state by the end of the century, according to studies by bird experts and climatologists.
Hundreds of bird species may already have died off or left for cooler climates in the past decades, experts say. Among those species at high risk are the California gnatcatcher, the cactus wren and the California towhee.
Between 25 percent and 50 percent of bird species native to southern California are predicted to disappear in the next 100 years, depending on how much humans do to curb global warming, according to a report by Audubon California that was a companion study to one by the National Audubon Society.
Bird species can tolerate only a certain range of temperatures, and climate change also affects their food and water sources, said Bill Monahan, a senior mapping scientist with Audubon California.
If an area gets warmer, some birds will move somewhere similar to their original habitat. But others will just die if they don't have the instinct to migrate or are too weak from lack of food to do so, he said.
As a result of droughts in 2002 and 2007, there have been fewer insects throughout the Inland valleys and deserts, he said. Fewer insects mean fewer lizards, and both serve as a food source for the shrike.
Rising average temperatures have also been drying up vital bird wetlands, including the Salton Sea in southeast California.. That has some biologists worried about the future of the crucial watering spot for birds living in or migrating through the Imperial Valley, Calif.
The loss of bird species could be a greater indicator of the future of Earth's ecosystem and how global warming may affect humans, as well as other animals that have sought cooler climates as their native habitats have warmed up, according to scientists
"They're starving to death and they may not be able to maintain their own selves and their young," said Gene Cardiff, a long-time bird watcher. "They're taking a beating."
While the Audubon reports also cited other factors that have affected where birds are found, it is the gradual rising of the earth's temperature that is the most significant cause, they said.
Tim Barnett, a marine physicist at the Scripps Institution of Oceanography at UC San Diego, said climate change can cause declines in birds' food and water sources. Migration changes and population reductions may be a direct result, he said.
Rising temperatures are also contributing to a scarcity of water in areas such as the Imperial Valley, Barnett said.
The Salton Sea is one of the last refuges for birds there, since development has converted 95 percent of the valley's wetlands into farmland, said wildlife biologist Robin Corcoran.
The sea is already being depleted by evaporation and for irrigation and drinking water, making its water even saltier than the Pacific Ocean. But warmer temperatures are speeding up the evaporation, Corcoran said, and scientists worry it could become too salty to support the fish that birds feed on.
Though ornithologists estimate the bird population loss could be minimized if people reduce greenhouse gas emissions, climatologists say the effects cannot be reversed and may be felt for the next 100 years.
E-mail John Asbury at jasbury(at)PE.com
(Distributed by Scripps Howard News Service, www.scrippsnews.com.)
Must credit The Press-Enterprise of Riverside, Calif.
