Birds of the Sierra Nevada. Ted Beedy

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Birds of the Sierra Nevada - Ted Beedy

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Warblers, Dark-eyed Juncos, and House Finches. The robins, bluebirds, and warblers mainly take advantage of fruits left over after fall harvest.

      Urban/Suburban

      In terms of bird habitats, urban and suburban areas usually offer a patchy mosaic of ornamental plantings, vacant lots, and remnant native habitats that occur between structures. Ornamental plantings in older neighborhoods are often mature, introduced evergreen and winter-deciduous trees that may be as much as 100 years old. These ornamental species range in height from approximately 20 to 50 feet high at maturity and are typically much smaller and younger than the occasional remnant oaks, pines, or incense cedars in these neighborhoods. Small lawns and mature hedges are also characteristic and include many introduced fruiting species that attract a variety of birds. Riparian or stream habitats occurring within urban and suburban landscapes usually accommodate the greatest number of species, such as Anna’s and Rufous Hummingbirds (at houses with feeders), American Crows, Steller’s Jays, Western Scrub-Jays, American Robins, Northern Mockingbirds, House Finches, Cedar Waxwings, Brown-headed Cowbirds, and Brewer’s Blackbirds, native denizens of parking lots. Introduced non-natives like European Starlings and House Sparrows are found almost exclusively in such areas. Bird feeders, an ever-increasing feature of these areas, attract and help sustain many of these birds.

      Recent Trends in Sierra Bird Populations and Ranges

      In this chapter we review changes in populations and ranges of birds of the Sierra over almost four decades. We used data from Breeding Bird Surveys (BBS) and Christmas Bird Counts (CBC) and supplemented those data with observations cited in North American Birds, numerous publications (see the bibliography), and the personal experience of ourselves and many regional experts. We also compare our analyses of BBS data with those of Sauer et al. (2011). Those authors used a different definition of Sierra boundaries, a different time frame, and more sophisticated statistical methodology (see Appendix 3). We have also, where possible, attempted to put these trends into larger state- or continent-wide perspective.

      There are 44 BBS routes and 25 CBC circles within the Sierra region (see Map 5). Most of these have been run throughout much of the past 35 years, providing a relatively robust, long-term dataset to explore. BBS routes are run during the spring and summer breeding season, and CBCs are run from late December into early January. Since many of the species counted during these surveys are migratory, the breeding season and wintering season birds may often be of different subspecies or from separate populations. Therefore, one should not necessarily expect that a given species should reflect similar trends from BBS and CBC data. BBS routes are limited to roads, so much of the Sierra (in particular the higher elevations) is not surveyed by these routes. CBC circles are almost completely limited to lower elevations that are accessible in the winter. Although both these sources have their limitations, when the data show significant and consistent trends over a number of circles or routes, one can be fairly confident they reflect real trends. We limited our analyses to species that are relatively common and widespread throughout the Sierra. Appendix 3 describes the methods we used to detect trends for each species.

      POSITIVE TRENDS

      Species that showed statistically significant positive population trends from either BBS or CBC data are summarized in Table 2. Of the 117 species we analyzed, more showed positive trends than negative ones. Population increases for several of the species can be attributed to direct or indirect effects of human activities. The California Department of Fish and Game first introduced Wild Turkeys into the state in 1908. However, those and all subsequent introductions (mainly using captive-bred birds) over the next 50 years proved unsuccessful. It was only when wild-captured birds from Texas began to be released from 1959 to 1988 that California populations began to become self-sustaining. Data from BBS and CBC surveys reflect the success of those efforts, with huge increases starting in the mid-1980s and continuing up to the present.

      MAP 5 Locations of Breeding Bird Survey (BBS) routes and Christmas Bird Count (CBC) circles used for trend analyses

      Large and growing, resident flocks of Canada Geese may be the result of a combination of factors including historical California Department of Fish and Game introductions (i.e., prior to the early 1970s), releases from private waterfowl breeders, and native wintering birds failing to migrate and producing nonmigratory offspring. Dramatic recoveries in populations of Bald Eagle and Osprey are likely due in large part to banning of DDT in North America in the 1970s. Eagles also benefitted from protection under the state and federal Endangered Species Acts. Increasing human population in the Sierra and the bird feeders which usually accompany that increase could be contributing to increases in Anna’s Hummingbirds and Lesser Goldfinches. These same factors have allowed House Finches to expand their year-round range into higher-elevation portions of the Sierra. Nest box programs are likely benefiting species like Wood Ducks, Western Bluebirds, and Tree Swallows. Planting of exotic, winter-fruiting trees in newly developing areas of the Sierra could help explain the increasing winter populations of American Robins, Cedar Waxwings, and Western Bluebirds, although increasing average winter temperatures could also be a factor.

      We found increases in seven species associated with chaparral/early successional habitats (Bewick’s Wren, Blue-gray Gnatcatcher, MacGillivray’s Warbler, Spotted and California Towhees, Rufous-crowned Sparrow, and Lazuli Bunting) or forest-chaparral edges (Dusky Flycatcher) (Figure 13). The increase in large-scale, stand-replacing fires in the Sierra in recent years may have expanded these types of habitats to the benefit of these species.

      FIGURE 13 Charts showing trends for selected species based on Christmas Bird Count (CBC) data (Spotted Towhee and Red-shouldered Hawk) or Breeding Bird Survey data (Dusky Flycatcher and Olive-sided Flycatcher). All trend lines are based on linear regression. Note that for CBC data, Count Year 76 is winter 1975–76 and so on.

      The trends for Brown-headed Cowbirds have been complex. Consistent with their historical spread throughout California in the past century, cowbirds followed human expansion and cattle grazing up into the Sierra, and our BBS data show a steady increase in numbers up to 1990. However, since then, the trend has been flat to negative. Analyses of BBS data by Sauer et al. (2011) showed a significant negative trend. CBC data show a slightly positive trend that is not statistically significant.

      NEGATIVE TRENDS

      Species that showed statistically significant declines based on either CBC or BBS data are summarized in Table 3. For most of the species on this list, a variety of different sources have documented long-term, widespread population declines throughout their North American ranges. Degradation of winter habitat in Central and South America has been implicated in the long-term declines seen in Olive-sided Flycatchers and Western Wood-Pewees. In addition, some forestry practices like postfire salvage logging may have contributed to the alarming negative population trend for Olive-sided Flycatchers (see Figure 13) in the West. Reduced quality of montane riparian habitats is a likely contributor to declines of Western Wood-Pewees, Yellow Warblers, and Wilson’s Warblers. Brood parasitism by Brown-headed Cowbirds is also implicated in Yellow Warbler declines. Killdeer, Horned Larks, and Lark Sparrows are among the 70 percent of grassland- associated birds that have shown highly significant population declines throughout North America.

      The steady decline in American Kestrel numbers across the continent has been studied intensively but remains largely unexplained. Extensive development in the lower elevations of the West Side of the Sierra Nevada may be partly to blame for the negative population trends for Lark and Chipping Sparrows, as both species are particularly sensitive to habitat fragmentation. Habitat fragmentation in its low-elevation breeding range may also be responsible for the declines in Bullock’s Orioles. Reasons for significant

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