RANGE CONTRACTIONS
While the news is mostly good, with many more Sierra bird species increasing in numbers and range than declining, we do have several species that have seen their ranges shrink substantially. For the most part, we have very poor understanding of the causes behind these changes. Two of the more perplexing examples of Sierra breeding range contractions are those of Ruby-crowned Kinglet and Swainson’s Thrush. Based on their status in the early 20th century, Grinnell and Miller (1944) considered both species to be common on the West Side of the Sierra, from the northern edge of the range south to Tulare County. Breeding populations of both species are now highly localized and very sparsely distributed in the region. BBS routes rarely record either species, even in places where the species was considered to be historically common.
In the past few years the Grinnell Resurvey Project has systematically surveyed areas covered by Joseph Grinnell and his associates and found both species missing from nearly all the locations where they were previously present (Moritz 2007). No convincing hypothesis has surfaced to explain these range contractions. CBC data suggest that the wintering population of Ruby-crowned Kinglets in California is stable. BBS data show declines for the kinglet in the Sierra and Cascade Range but not in the Rockies. Swainson’s Thrushes breeding in coastal California, while showing declines based on BBS data, still occupy most of their historical range in that region.
Greater Roadrunners, once relatively common and widespread in the western foothills of the Sierra, are now patchily distributed and rarely encountered in much of this part of their range. Historically, throughout most of California, conversion from rangeland to more intense forms of agriculture and increasing human development has coincided with the disappearance of this species. At least into the 1930s, Willow Flycatchers were still considered common throughout the Sierra in any area with suitable riparian/willow habitat. Today the species is the scarcest of all our Sierra flycatchers and persists in only few areas. Habitat loss from reservoir construction and water diversions and habitat degradation from overgrazing, combined with the incursion of Brown-headed Cowbirds into the Sierra, have all been blamed for their decline.
With Sierra temperatures predicted to continue rising, vegetation zones are likely to move upslope with changing climate. This could push species using the highest elevations, like American Pipits and Gray-crowned Rosy-Finches, toward extirpation from the Sierra. Because their breeding areas are difficult to reach, we have little data on breeding season trends for either species, but winter numbers of American Pipits in California have shown significant declines over the past 30 years.
Unanswered Questions about Sierra Birds
As much as we know about Sierra birds, there is even more we do not know. Unanswered questions abound, and many of these questions offer opportunities for amateur naturalists to make significant contributions. We urge all visitors to the Sierra to take careful notes and record all their observations using eBird (http://ebird.org/content/ebird/). Below we list just a few of these questions. Please refer to the “Family and Species Accounts” section of this book for more details.
What is the current breeding range of the Harlequin Duck in the Sierra?
Recent observations suggest that these rare ducks are beginning to recolonize the Sierra, but all known occurrences are in steep river canyons where most birders never venture. Careful breeding season observations by sturdy hikers who pay attention to birds will give us a much better understanding of their current distribution and conservation status.
What are the current breeding ranges of Ring‑necked Ducks, Buffleheads, and Hooded Mergansers in the Sierra?
In recent years all three of these ducks appear to have extended their breeding ranges farther south into the Sierra than previously thought. Careful breeding season observations at mountain lakes could yield important information on distributional changes of these species.
Are rapidly increasing populations of Eurasian Collared-Doves and Great-tailed Grackles having an impact on other birds?
The rapid expansions of both these species in California seems likely to affect other birds. By making consistent obsevations of numbers of birds in a given area and by recording any changes in their breeding status and behavior, birders could help reveal impacts of these new arrivals.
How many Black Swifts breed in the Sierra?
Although we are aware of only a handful of breeding locations for this species in the Sierra, recent intensive surveys of likely sites (waterfalls with a specific set of characteristics) in the Rocky Mountains revealed many more birds than expected. Exploring similar sites in the Sierra could produce similar results.
Where do Williamson’s Sapsuckers and Pine Grosbeaks spend the winter?
Neither species is commonly found at high elevations in winter. The sapsuckers are occasionally found at lower elevations (even down to the Central Valley) very rarely, but the grosbeaks seem to simply vanish in winter. Hardy birders venturing into the high Sierra in winter, and very observant birders anywhere, could add much to our knowledge of the movements and winter whereabouts of these species.
Do Black-backed Woodpeckers require recently burned forests?
The California Department of Fish and Game is currently evaluating whether this species warrants listing as either Threatened or Endangered. The species apparently prefers intensively burned forests over unburned forests and forests that have burned at lower intensities, but it also uses unburned forests. A better knowledge of their dependence on burned forests, and their occurrence in unburned forests, would be of great value to public agencies and private landowners.
What is the extent of the “return” of Bell’s Vireos to the Sierra?
Previously extirpated from the region, this species appears to be staging a comeback. Birders would do well to learn their distinctive songs and be on alert for new locations, especially in riparian forests of the southern Sierra.
How are Purple Martins faring in the Sierra?
Recent increases in the extent and intensity of wildfires has created more areas with large fire-killed trees (snags) that may provide nesting habitat for martins. Visits to these landscapes in early summer could reveal new nesting locations as well as information about the presence of European Starlings and other competitors for nesting sites.
What are the exact range limits of the two Sierra subspecies of White-breasted Nuthatch?
These subspecies (which may someday be recognized as separate species) have distinct calls, as described in the “Family and Species Account” section of the book. Birders who learn the difference can help us understand the true ranges of these taxa in the Sierra.
What is the range of Pygmy Nuthatches on the West Side?
This species spills over onto the West Side here and there, especially in the northern Sierra. We do not have a precise knowledge of all the places where these nuthatches regularly occur, or of their seasonal status at these locations.
What happened to breeding Ruby-crowned Kinglets and Swainson’s Thrushes in the Sierra?
Formerly fairly common and widespread as breeders, both species have disappeared from most of their historical breeding range in the Sierra. Other populations (kinglets in the Rocky Mountains and thrushes of the Pacific Coast) seem to be stable. Any breeding season observations of these species in the Sierra should be reported via electronic discussion lists and/or eBird.
What are the current breeding ranges of American Pipits and Gray-crowned Rosy Finches in the Sierra?
These species have been confirmed to breed at a handful of high-altitude locations. Birders visiting alpine regions of the Sierra in summer should be on the alert for them, as both species are likely to be affected by climate change.
Bird Conservation in the Sierra
HISTORY
Human impacts on the Sierra and its birdlife began