FIGURE 12 Developed habitats (cropland)
DEVELOPED HABITATS
Forage Crops, Irrigated Pastures, and Croplands
Forage crops, such as grass hay and alfalfa, nearly always consist of a single species that may be annual or perennial. Most forage crops are planted in the spring and harvested in summer or fall and in the Sierra mostly include hay and alfalfa. For the most part, forage crops and irrigated pastures are planted in fertile soils in alluvial valley bottoms or gently rolling terrain in the low to mid-elevations of the Sierra, and most are found on the East Side. They are often adjacent to annual grasslands, ephemeral or perennial streams, or irrigation canals, which increases their attractiveness to such birds as Northern Harriers, Red-tailed Hawks, American Kestrels, Mourning Doves, Western Kingbirds, American Crows, Black-billed Magpies (East Side only), Western Meadowlarks, Brewer’s Blackbirds, and Red-winged Blackbirds. By far the most impressive examples of these habitats are in the Sierra Valley (Plumas and Sierra Counties), where, in conjunction with marshlands and wet meadows, these habitats attract impressive numbers of waterfowl and wintering raptors, nesting Sandhill Cranes, shorebirds, and waterfowl.
Orchards and Vineyards
Compared to all-natural habitats, orchards and vineyards are relatively barren of breeding birds. In some parts of the Foothill zone, largescale conversion of annual grasslands, oak savannas, and oak woodlands to orchards and vineyards has resulted in direct losses of bird habitat. Typical birds that forage in orchards include Mourning Doves, American Crows, Yellow-billed Magpies, American Robins, and House Finches. Compared with orchards, vineyards are usually grown in rolling hills with deeper, well-drained soils. They are managed intensively and the soil under the vines is generally sprayed and barren to prevent the growth of grasses and other herbs, which reduces their value to bird life. Huge flocks of introduced European Starlings visit vineyards, especially in late summer and fall when they may consume entire crops of ripening grapes. A few native birds that forage in vineyards opportunistically include Mourning Doves, Western Scrub-Jays, American Crows, American Robins, Western Bluebirds, Cedar Waxwings, Yellow-rumped 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