Bye-bye birdie?

Winter flocks of the tricolored blackbird were once said to darken the skies as they flew around California’s freshwater wetlands, where they primarily live. Researchers in the 1930s counted more than 700,000 breeding adults of the species in the Central Valley alone. However, a statewide count found fewer than 233,000 adults in 1997, as years of unchecked human development encroached on the bird’s habitat, forcing the blackbird to venture to new agricultural areas less conducive to foraging.

Last December, volunteers with the Audubon Society conducted the 108th annual Christmas Bird Count. While the findings won’t be available until mid-February, Tim Fitzer, vice president of the Sacramento chapter, expects results for many species to mimic results of the last several decades: declining populations nationwide.

Listening to Fitzer discuss the decline of bird species around Sacramento felt like a lesson in Zen living. Far from sounding alarmed, he sounded more resigned, explaining the situation as though this is exactly what he expected to happen. While he said all bird species are in flux—numbers grow or decline depending on weather conditions and availability of food—decreasing numbers are still cause for concern, especially when one of the biggest threats birds face doesn’t seem to be going away anytime soon. That threat? Habitat loss.

“The birds are moving into areas where there’s foraging available for them,” said Fitzer, who has led birding trips for almost three decades. “If [developers] build malls and houses, the birds will just go to a different area.”

Admittedly, bird counting is a tricky business. During the Audubon Society’s yearly counts, volunteers all over the United States spend about three weeks in fields, forests and marshlands counting, sketching and documenting the country’s diverse avian species. In the Sacramento area, counters spread out in a 15-mile diameter circle, which is then divided into 10 areas, each one of them headed by a count leader that collects data at the end of the day. Although Fitzer concedes that thousands of birds may go uncounted, volunteers gather enough data for general population trends to emerge.

Every year the Audubon Society publishes a WatchList that documents those bird species most in danger of extinction. Several factors, including population size, bird distribution or even specific threats, such as a proposed-development site, determine the birds that make the list, which is then used to identify species most in need of limited conservation resources.

Of the 217 species named in the 2007 WatchList, more than one-third are native to California, including California condors, ashy storm-petrels, tricolored blackbirds, long-billed curlews and snowy plovers. Part of the reason so many California birds make the list is because of the state’s rich biodiversity. California’s deserts, mountains, shoreline and valleys host a wide range of species that rival many other states. But as those diverse habitats are developed to make way for human growth, bird species native to these lands will eventually have no other place to go.

The loss of birds isn’t limited to California. From Washington to Florida, Canada to Peru, land and seabirds across the Americas are disappearing by the millions. A recent report from the Audubon Society revealed that the population of 20 of the most common species of American birds declined by at least 50 percent over the past 40 years.

The northern bobwhite, native to the East Coast, is threatened by farmers replacing natural warm-season grass—which the birds need for nesting and brood-rearing—with exotic cool-season grasses. Global warming melts away the permafrost crucial to Alaska’s greater scaup, and deforestation in Venezuela drives away monkeys and sloths, the main food source of the harpy eagle, the world’s strongest bird of prey.

In each case, the bird populations prove highly susceptible to environmental factors, including yearly rainfall, food supplies and illness. In the Sacramento region, for example, falling numbers of the loggerhead shrikes and yellow-billed magpies are probably due to infection by West Nile virus, according to Fitzer.

While infection and global warming are partly to blame for these species’ declines, Rodd Kelsey, an ecologist for Audubon California’s Landowner Stewardship Program, agreed that habitat loss is by far the biggest threat. And human population growth in the Central Valley will only worsen the problem.

“Imagine doubling the population along the I-5/I-99 corridor,” he said, and what that would do to the remaining farmland and natural habitat the birds rely on. One thing’s for sure: It won’t be pretty.

Fitzer pointed specifically to development in Folsom, Natomas and south Sacramento over the past 20 years as reason for the shrinking bird counts.

“Look at all the expansion of houses and whatnot over the Sacramento area. Look how much it’s grown,” he said. “Where there used to be orchards there [are] houses now in a lot of places.”

As California’s population grows, the need for larger and more productive farms also increases—another factor impacting bird species here.

Intensifying agricultural activity can make it difficult for birds to nest and forage. Fields used for constant crop production decrease the water quality, employ higher machine activity—which can destroy bird nests and eggs—and make the land less able to sustain wildlife. Kelsey works with farmers to make fields more eco-friendly. In some cases, farmers are paid to delay harvesting long enough to allow eggs in their fields to hatch.

Despite the decreasing numbers, there are signs of hope. One of the best-known comeback stories is that of the California condor, which had been reduced to only 22 individuals in 1998. Policy work and legislation aimed at protecting the species helped bring the numbers back up to roughly 300 birds, 79 of them in the wild.

So why should humans be concerned about any of this? For one thing, birds eat insects dangerous to California crops. But there is perhaps another, more ominous reason. Historically, miners used canaries to warn of lethal, undetectable gas build-ups far below the earth’s surface. A dead bird in a cage alerted them to stop what they were doing and get to safety. Perhaps birds are sending us a similar message now.

In his 2006 book, The Creation: An Appeal To Save Life On Earth, Pulitzer Prize-winning biologist Edward O. Wilson cautioned readers about the inflating rates of plant and animal extinction around the world. “If this rise continues unabated,” he wrote, “The cost to humanity, in wealth, environmental security, and quality of life, will be catastrophic.”