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Bird Conservation in the Sierra

HISTORY

Human impacts on the Sierra and its birdlife began thousands of years before European settlement. Native peoples used fire as a management tool to clear brush, maintain grasslands and meadows, make travel easier, and improve browse for game animals. Fire management, hunting, fishing, and gathering by Native Americans affected plant and animal communities in the Sierra and likely altered the relative abundance and distribution of some bird species long before the first Europeans arrived.

Changes caused by native peoples over a 10,000-year span prior to the 19th century paled in comparison to the impacts of European settlers and their large-scale, aggressive use and abuse of Sierra resources. Forests were logged extensively, with the largest trees targeted, and sheep and cattle swarmed over mountain meadows that had never experienced such intense grazing pressure. At lower elevations exotic annual grasses were introduced and dominated the grasslands and savannas so quickly that no naturalist was ever able to observe or describe the pre-European plant communities. Some speculate that native bunch grasses dominated, but the true nature of these original landscapes and most Sierra plant communities remains unknown.

The discovery of gold in the Sierra foothills in 1848 dramatically accelerated these impacts and added to them demolition of hillsides (typically with powerful water cannons) and diversions and excavations of nearly every stream on the West Side from Butte County south to Madera County, all in a frantic search for gold. The top predators, grizzly bears and wolves, were systematically exterminated. To encourage railroad companies to invest in the transcontinental railroad in the late 19th century, the United States gave large swaths of Sierra land to these companies by granting them every other section (a one-mile by one-mile square) of land along the proposed route. The result was a checkerboard of public-private ownership that has inhibited rational conservation planning ever since. One of the most direct effects on Sierra birds including ducks, geese, quail, and grouse came from “market hunting” to feed burgeoning gold rush populations as well as rampant shooting and persecution of raptors.

We can only speculate about the impacts on birds from all these changes because no comprehensive, large-scale studies of Sierra wildlife were conducted until the early decades of the 20th century. Logging of large trees almost certainly decreased the available habitat for species such as Northern Goshawks, Spotted Owls, and Pileated Woodpeckers. Grazing of mountain meadows degraded these habitats and must have reduced habitat for Willow Flycatchers, Yellow Warblers, and Lincoln’s Sparrows. Gold-mining degraded streamside habitats for riparian-associated birds, including a diversity of migrating neotropical songbirds such as flycatchers, vireos, warblers.

Changes in public attitudes about nature and wildlife over the past few decades have eliminated or modified most of these historically damaging practices, and state and federal agencies are now tasked with managing public lands and wildlife resources using science-based approaches that help protect and enhance habitat for Sierra birds. Hunting is now highly regulated, and raptors are protected and mostly revered by the public. Logging, grazing, and mining practices are all regulated in an attempt to balance resource extraction with protection of natural resources, and riparian and wetland areas are being protected and enhanced as never before. The U.S. Forest Service and numerous nonprofit conservation organizations have actively worked to acquire land to eliminate the checkerboard pattern of ownership in the Sierra and strive to restore and enhance ecosystem processes and habitats where possible.

FIRE AND CURRENT FORESTRY PRACTICES

Fire regimes in the Sierra prior to European settlement likely consisted of frequent, low-intensity fires started by lightning or native people, maintaining an open-forest understory and supporting development of large areas of mature forest. Stand-clearing fires certainly also occurred and the resulting landscape was probably characterized by a mosaic of many different plant communities. Frequent chaparral fires maintained broad swathes of vegetation in early successional conditions and fire in grasslands and oak savanna created patches of open, treeless expanses. All these conditions would have produced a variety of habitats supporting a correspondingly high diversity of birds. Aggressive fire suppression in the Sierra began in the early 1900s and became more widespread and effective through the 1950s. Ironically, the major legacy of those years of fire suppression is a landscape that has higher densities of younger trees and denser understory, providing fuels that increase the frequency and size of large-scale, high-intensity fires.

More recently, forestry practices have recognized the important role of fire in the Sierra ecosystem. National Parks like Yosemite and Sequoia now have policies that allow most lightning-caused fires to burn, and also include controlled burns to reduce fuel levels. On publicly owned lands, fire-suppression policies have also been modified, and controlled burns are part of the management strategy. However, consideration given to commercial timber harvesting priorities, air quality, and nearby human residential areas all make implementation of these policies difficult. Experiments using selective logging to change fire behavior to reduce the risk of large stand-clearing fires are being conducted throughout the Sierra. It remains to be seen whether these practices are effective or economically practical. Their impact on wildlife is also difficult to predict. In any case, to the extent that birds have adapted to current conditions, any changes are likely to be detrimental to some species and beneficial to others.

In spite of the fact that old growth forests occupy less than one-fifth of their historical extent, these mature forests are still being logged both on private land and to a lesser extent on National Forests, further stressing birds that require this forest type. Even where protected from logging, the historical lack of fire has increased the density of shrub understory and smaller trees and increased the risk that this dwindling forest type could be lost to high-intensity fire. Clear-cutting and planting of even-aged, single-species tracks continues on private lands with a corresponding decrease in habitat diversity for birds and other wildlife.

One of the most problematic ongoing forestry issues is postfire salvage logging. When stand-clearing fires occur, the resulting landscape looks like a wasteland to the general public and represents an opportunity to harvest many large trees for commercial timber interests. However, a large and rapidly growing body of research (much of it conducted by the U.S. Forest Service) shows that removal of all or most of the largest standing dead trees (snags) is detrimental to a wide variety of cavity-nesting birds such as woodpeckers and bluebirds as well as other species that make extensive use of these landscapes for foraging (e.g., Olive-sided Flycatchers and Black-backed Woodpeckers). Much needs to be done to bring salvage logging policies in line with the best conservation science. In addition, forestry practices like herbicide application to suppress shrub growth and to accelerate regrowth of trees may not only be counterproductive, they may alter the succession of different habitat types that support diverse bird communities.

MOUNTAIN MEADOWS

Historical, unregulated overgrazing was so pervasive throughout the range that most experts in this field believe that not a single pristine Sierra meadow system remains. Many areas of these habitats have been altered right down to the basic hydrology that supports the entire meadow system. Eroded streams incise and cut deep channels, lowering water tables such that even when grazing is removed, the system cannot return to its prior wetland state without active intervention by restoration ecologists. However, grazing is now much reduced and more highly regulated, and efforts to restore these meadows are producing encouraging results. The U.S. Forest Service has partnered with other federal and state agencies and nonprofit conservation organizations to implement multiple restoration projects throughout the Sierra.

DAMS AND WATER DIVERSIONS

No major river system in the Sierra has been spared the impacts of dams or water diversions to provide water for human uses and to control flooding. While reservoirs have destroyed hundreds of miles of riparian habitat and drowned thousands of acres of meadows, likely contributing to the decline of the Harlequin Ducks and many meadow-dependent species, they have also created habitat that many species of water birds such as ducks, geese, and grebes have been quick to exploit. More recently, recovering populations of Bald Eagles and Ospreys are taking advantage of these human-made lakes to the point where they could be more numerous now in the Sierra than historically. Similarly, the massive diversion of foothill streams and the resulting canal systems that began with gold mining have led to the accidental creation of perennial wetlands in the north-central Sierra that have enabled the state-Endangered Black Rail to successfully colonize these areas. These changes are both a testament to the massive destructive power of humans and the remarkable adaptability of birds.

INTRODUCTIONS OF NON-NATIVE SPECIES

While European Starlings, Rock Pigeons, and House Sparrows may be the most visible of the non-native Sierra birds, no species has had a larger impact on native breeding birds than Brown-headed Cowbirds. Originally native to the Great Plains, where they followed herds of bison and pronghorns, cowbirds were unrecorded in California before 1870, although some may have been present on the East Side of the Sierra decades before that. By the 1930s, however, they were common and widespread in the Central Valley and Sierra foothills as they spread northward from Mexico and Arizona, taking advantage of the livestock grazing that accompanied human incursions into the Sierra.

Since then, they have moved steadily into higher and higher elevations. Sierra birds have not adapted to this brood parasite that lays its eggs in the nests of other birds. Effects remain relatively localized at higher elevations but are widespread in much of the low- and middle-elevation habitats that support more abundant cowbird populations. The populations and ranges of susceptible host species such as Willow Flycatchers and Yellow Warblers shrank dramatically because these species were unable to successfully fledge their own young while simultaneously raising a cowbird chick. The introduction of aggressive cavity nesters such as European Starlings and House Sparrows has likely impacted some native cavity-nesting birds. However, the fact that starlings and House Sparrows are mainly associated with urbanized areas has limited their impacts in the Sierra. It is hard to assess whether or not more recent intentional introductions (e.g., Wild Turkeys and White-tailed Ptarmigans) or rapid range expansions (e.g., Great-tailed Grackles and Eurasian Collared-Doves) will affect native Sierra birds in the future.

POLLUTION, PESTICIDES, AND OTHER ENVIRONMENTAL CONTAMINANTS

There may be no more compelling conservation success story than the one surrounding the banning of DDT in the United States in the late 1970s. This pesticide caused eggshell thinning, which had devastating impacts on populations of many bird species (see the “Family and Species Accounts” section of the book for the accounts of Bald Eagle and Peregrine Falcon as examples). Once the link was proven and the compound banned, the affected species recovered to the point that some have been removed from the Endangered Species List.

Continued diligence and careful research on pesticides is needed, however, as hundreds of new chemicals enter the environment every year and there is generally little testing for impacts on wildlife. Some have suggested links between environmental contaminants and recent widespread declines in some species such as Loggerhead Shrikes and American Kestrels. However, no solid evidence has emerged to confirm a link or identify a specific compound. Human development along the shores of Lake Tahoe has contaminated the once-pristine waters there, and air pollution from urban traffic has severely affected air quality in the foothills east of Sacramento, which has been shown to stress pine trees and other native vegetation and could be leading to subtle habitat changes. Direct impacts on birds have yet to be shown in either case, but degradation of water or air quality is likely to have widespread consequences across the entire natural community.

LAND USE CHANGES

Although many recent trends in human attitudes and practices are cause for optimism, land use changes in recent decades pose major threats to some Sierra habitats. The most serious threats are to the grassland, savanna, and chaparral habitats of the West Side foothills. Nearly all these lands are in private ownership and could be developed in the future. In recent decades residential and rural residential development has impacted the foothills more than any other part of the Sierra. In addition, thousands of acres have been converted from relatively wildlife-friendly cattle ranching to orchards and vineyards. As compared to the huge vineyards in the Central Valley that consume entire landscapes, much of the vineyard land in the Sierra occurs in smaller patches within a matrix of natural habitats. However, large contiguous areas of habitat are fragmented into smaller and smaller parcels, and efforts to protect homes and crops from the threat of fire (a natural, and critical, component of these ecosystems) impact all the land adjacent to these new land uses.

SIERRA BIRDS IN A CHANGING CLIMATE

Predicting the impacts of global climate change on the Sierra and its birds is particularly challenging. The nature of California’s climate is inherently complex due to the effects of long-term and short-term weather pattern cycles in the Pacific Ocean and the highly varied topography of the state. While California has seen some warming during the past century, the changes are less dramatic than in many other regions of the United States. Most climate models predict a warmer Sierra climate, possibly including more precipitation, but with more of that precipitation falling as rain instead of snow. These models also predict that by the second half of the 21st century, temperatures in the Sierra foothills could increase by 3.5° to 7.5° F and the frequency of extremely hot days (greater than 100° F) could almost double. Data from recent studies from areas of the Sierra first surveyed a century ago suggest that birds are indeed gradually moving (generally upslope) to remain within relatively similar climate zones.

As the climate changes, bird species are expected to shift their distributions independently, in some cases resulting in combinations of co-occurring species that have not been seen before. Species using the highest altitudes for breeding (e.g., American Pipits, Gray-crowned Rosy-Finches) may be unable to find suitable habitat in the future. Changes in winter snow-pack and spring temperatures could affect downstream riparian systems by reducing the amount of water and changing the seasonal timing of peak flows. These changes could alter the streamside vegetation and effect birds using those habitats.

HOPE FOR THE FUTURE

A historic 1994 decision by the State Water Resources Control Board reversed a long-term decline of the Mono Lake ecosystem caused by more than fifty years of water diversions from its principal tributary streams. This decision restored the stream flows and will eventually increase the surface elevation of Mono Lake to an average of 6,392 feet, which should ensure that this critical ecosystem will provide suitable habitat for myriad water birds in the future. Ongoing restoration efforts at Owens Lake and the upper Owens River, also degraded by historic water diversions, are also important steps toward restoring essential bird habitats in the eastern Sierra.

Two comprehensive reviews of the conservation status of the Sierra, the Sierra Nevada Ecosystem Project (SNEP) (California Resource Agencies 1996) and the Sierra Nevada Framework analysis (U.S. Forest Service 2001) came to the identical conclusions that this region faces urgent threats. In 2004 the SNEP report helped catalyze the formation of a new state agency, the Sierra Nevada Conservancy, which has the mission of initiating and supporting efforts that “improve the environmental, economic and social well-being of the Sierra Nevada Region, its communities and the citizens of California.” This organization is tangible evidence of the high value that Californians place on protection of the Sierra and recognition that land use policies and management must focus on maintaining healthy ecosystems that provide high-quality water, spectacular scenery, and important wildlife habitat for all of California.

SUMMARY

Despite the challenges described here, we have good reason to be hopeful about bird conservation in the Sierra. Never before have so many people cared so deeply about nature in general, and birds in particular, and been willing to work to preserve natural habitats. Regulatory protections in place today would have been unthinkable even 50 years ago, and the new Sierra Nevada Conservancy provides a forum for collaborative, science-based approaches to managing Sierra bird and other wildlife populations. Most of the Sierra above the foothills is in public ownership, and many of the largest private landowners have strong commitments to good land stewardship.

Birds demonstrate to us again and again their astounding capacity to adapt. Indeed, the data summarized in the chapter “Recent Trends in Sierra Bird Populations and Ranges” suggest that more species in the Sierra are increasing than decreasing. More than almost any other organisms, birds are highly mobile, and many species can find and colonize new areas of habitat quickly. As human populations continue to increase and competition for critical resources like water and open space becomes more intense, we must combine our capacity to invent with our unique capacity to appreciate the inherent value of other species and create solutions that maintain viable, diverse populations of birds in the Sierra and elsewhere.