Читать книгу Birds of the Sierra Nevada - Ted Beedy - Страница 13
ОглавлениеEcological Zones and Bird Habitats
The Sierra offers an extraordinary variety of bird habitats, from the rolling foothill grasslands, through oak studded savannas and giant conifer forests, up to alpine meadows and chilly, windswept peaks, and over the crest to the lakes, forests, and sagebrush flats of the East Side as well as Joshua tree woodlands of the southern desert regions. No wonder Sierra bird life is so varied! The West Side boasts an elevation gradient unequaled in the 48 contiguous states, spanning nearly 14,000 feet from the lowest foothills to the highest peaks (see Map 2). Most of the Sierra lies west of the divide, and the East Side drops off sharply to the Great Basin. On this steep eastern escarpment, altitudinal vegetation zones overlap extensively, making them less apparent than on the West Side. North of Lake Tahoe the main crest is flanked on both sides by other ridges and the elevation of the crest itself is lower, making the distinction between the western and eastern Sierra less obvious. The Kern Plateau in southeastern Tulare County is an area that does not fit neatly into the zones described below. It includes ecological elements from both sides and is an area where species normally associated with the East Side (e.g., Pinyon Jay) occur on the West Side, and where other species are found at much higher altitudes than elsewhere in the Sierra (e.g., Lawrence’s Goldfinch).
In this book we have recognized seven major ecological zones: Foothill, Lower Conifer, Upper Conifer, Subalpine, Alpine, East Side, and Desert (see Table 1; Map 3). Note that the elevation ranges are approximate and overlap considerably. Local differences in slope, soils, rainfall, and other factors alter the exact range of any ecological zone. As discussed in this chapter, most of these zones include several distinct bird habitats. Sierra watersheds and key locations are shown in Map 4. Common and scientific names of all plant species are provided in Appendix 4.
MAP 2 Elevational zones
MAP 3 Ecological zones
MAP 4 Watersheds and key locations mentioned in the text
TABLE 1 Approximate elevations and total area of Sierra ecological zones
FOOTHILL ZONE
Annual Grasslands
North <500 to 2,000 feet; South <500 to 2,500 feet
Many travelers pass through annual grasslands without registering them as “habitat.” This open (less than 10 percent tree cover), gently rolling terrain is parched to a golden brown in summer but transforms to vivid green in late fall through early spring. Patches of this habitat in the Sierra are found in eastern Tehama and Butte Counties and westernmost El Dorado County, but the largest expanses are found from western Tuolumne County south into Kern County. Because no naturalists were present in pre-European times to document the conditions, we do not know what plant species dominated this landscape, and there is considerable controversy about whether perennial grasses or forbs were the most abundant plants. Even before European settlement, Native Americans had been managing these areas with fire for thousands of years. In any case, they are now dominated by introduced grasses brought by European settlers. A high diversity of indigenous plants still survive in vernal pools or intermixed with the non-native species. In many areas woodland and chaparral were cleared to create grazing land and are now annual grasslands. In spring, wildflowers still flourish in the foothills, and specialized blooms form rings around the receding waters of vernal pools. Recent research has shown that cattle grazing—by far the dominant land use in this habitat—is actually beneficial for most native vernal pool plants and most grassland birds, at least partly because grazing keeps aggressively invasive plants like star thistle and medusa head in check and prevents thatch buildup that inhibits growth of many native plants.
Wintering Horned Larks and American Pipits flock together in grazed pastures and plowed furrows, and Savannah Sparrows forage in the deeper grasses, each species constantly wary of the risk of a Prairie Falcon attack. Annual grasslands provide abundant food and cover for high numbers of rodents and other small mammals and therefore support an impressive variety of raptors with winter migrants augmenting resident Red-tailed Hawks and American Kestrels and species like Ferruginous and Rough-legged Hawks visiting only from fall through early spring. In spring, American Kestrels, Western Kingbirds, and Loggerhead Shrikes stake out territories on fence lines or on “tombstones” of ancient metamorphic rock that rise abruptly here and there. The lovely songs of Western Meadowlarks can be heard almost any month of the year. On hot afternoons Turkey Vultures float lazily above low ridges and hillsides.
FIGURE 1 Foothill zone
Oak Savannas
North < 500 to 3,000 feet; South <500 to 2,500 feet
Savannas dominated by blue oak occupy more than a million acres of the Sierra foothills. These habitats have 10 to 30 percent tree cover and vary from grasslands with a few widely spaced trees to denser stands that may also support interior live oaks, California buckeyes, and occasional gray pines. The extent of oak savanna in the foothills has been reduced through conversion to developed and agricultural land uses, woodcutting, and historical efforts to improve grazing land by clearing trees. Range managers have now learned that having oaks on the land actually improves the forage for cattle by allowing the shaded grasses to retain water.
This quintessentially California landscape is threatened by a widespread lack of natural regeneration of oaks. Although the impacts of grazing have certainly affected the ability of these trees to reproduce, it has been shown that simply removing grazers does not aid regeneration. Other factors, like competition with nonnative plants for scarce water (mainly at the seedling or sapling stages), are also critical to oak survival. In fact, removing grazers entirely can inhibit oak regeneration because of the deep thatch and explosion of invasive weeds that usually follows. Encouraging results have been seen with a combination of protection of seedlings and saplings from grazing and management of competing vegetation, followed by a well-managed grazing regimen. Western Scrub-Jays have historically been the main agents of oak regeneration because acorns they bury but fail to recover have a good chance of germinating; since acorns do not roll uphill, jays and squirrels must move them there. Oaks have evolved a boom-and-bust cycle of acorn production to guarantee that in boom years there will be far too many acorns for the jays to consume.
Oak savannas provide perching and nesting sites for several species of raptors as well as for a stunning variety of songbirds like Lark Sparrows, Western Kingbirds, Bullock’s Orioles, and Western Meadowlarks. As the oaks age or die, they provide essential nesting habitat for a variety of cavity nesters such as Acorn and Nuttall’s Woodpeckers, Oak Titmice, Ash-throated Flycatchers, White-breasted Nuthatches, Bewick’s Wrens, and both Violet-green and Tree Swallows. Some winters, large numbers of richly colored Lewis’s Woodpeckers visit oak savannas.
Oak Woodlands
North 1,500 to 4,500 feet; South 2,000 to 5,500 feet
Above the grasslands and oak savannas, denser oak groves of more than 30 percent tree cover crowd the hillsides of the western Sierra. In addition to blue and interior live oaks, three other species dominate: valley oaks, California black oaks, and canyon live oaks. All are long-lived and sprout from their stem bases when cut or top-killed by fire. Otherwise, there are considerable differences in their ecology. Valley oaks are large deciduous trees that dominate some riparian forests and open woodlands on fertile, deep soils. Similar to blue oaks, valley oaks suffer from limited recruitment of saplings. Blue oaks tolerate thinner soils and drier conditions than valley oaks and are the most likely oak to be found in uplands well away from drainages. Interior and canyon live oaks are evergreens and vary in growth from low shrubs to large trees. In steep ravines and river canyons these oaks cling to rocky slopes, while toyon, California bay laurel, and redbud grow in cooler glades below. Gray pines, with their wispy, gray green needles, grow along with the oaks in the northern and central Sierra and in the extreme south.
In spring, oak woodlands come alive with the songs of Orange-crowned and Black-throated Gray Warblers, and the roughly whistled notes of Ash-throated Flycatchers. The Hutton’s Vireo’s monotonously repetitive song is a frequent sound in stands dominated by live oaks. White-breasted Nuthatches search the deeply furrowed bark of these trees and sound their nasal, hornlike calls. Northern Pygmy-Owls hide in these canyons by day and emerge at dusk to hunt for songbirds. In the Mother Lode country of the central Sierra, Highway 49 cuts through broad expanses of foothill woodland and chaparral, where one might still spot a Greater Roadrunner. On nearly any turnout, the strident calls of Western Scrub-Jays or Oak Titmice can be heard. California Quail work through tangles of poison oak, and Acorn Woodpeckers flash back and forth between trees, flycatching, chattering, and tending their acorn caches.
Foothill Chaparral
North <500 to 4,500 feet; South 500 to 5,500 feet
Impenetrable seas of brush cover hot, dry slopes the length of the Sierra foothills. Interspersed with foothill woodlands, chaparral vegetation generally occupies the steeper, more arid exposures, and the most extensive stands occur south of the San Joaquin River. Turnouts along the new Priest Grade (Highway 120), near Ash Mountain in Sequoia National Park (Highway 198), and the near vertical slopes above the South Fork Kern River (Highway 178) provide easy places to view these habitats. Visitors to foothill chaparral will notice pungent odors of chamise, whiteleaf manzanita, buckbrush, coffeeberry, and shrubby oaks filling the air. These shrubs grow together in thickets forbidding to people but offering shade and shelter to birds. Chaparral birds usually sing, defend territories, and forage in the cool, early morning hours.
Presunrise visits to these arid shrublands are often rewarded by a chorus of Common Poorwills, Wrentits, California Thrashers, Lazuli Buntings, and Spotted and California Towhees. As early as January, Anna’s Hummingbirds defend patches of shrubs with squeaky calls, and in spring Blue-gray Gnatcatchers and “Bell’s” Sage Sparrows (in chamise chaparral) raise their families within this protective cover. Birds can be particularly abundant in foothill chaparral habitats because they exist below the snow zone and because many native shrubs, such as toyon and poison oak, produce fruits that attract such species as American Robins, Cedar Waxwings, and Hermit Thrushes.
Foothill chaparral is a fire-prone system and the health and diversity of this habitat depends on fire. Many of the shrubs can survive fire and sprout from their burned stumps. Many others produce seeds than can only germinate after a fire. This habitat goes through a postfire succession, analogous to that of conifer forests, but at a much-accelerated pace. The open ground following a fire soon fills with a dazzling array of wild flowers. In the first postfire years birds like Rufous-crowned Sparrows, Lazuli Buntings, and Lawrence’s Goldfinches find conditions perfect. As the chaparral grows denser over time, new species appear and others depart. When the habitat becomes heavily overgrown and the shrubs reach their maximum height and density, bird diversity tends to decline, awaiting the next fire to begin the cycle again.
LOWER CONIFER ZONE
Ponderosa Pine Forests
North 2,000 to 6,000 feet; South 2,500 to 7,000 feet
Rising above the heat and haze of the Foothill zone, the Lower Conifer zone is where many people first feel they have reached the mountains. Breezes rustle the trees and, though hot in summer, these forests are distinctly cooler than the lowlands. They also receive more rainfall and snow, enabling them to survive the summer drought. Historically, ponderosa pines were the most common and widespread trees in the Lower Conifer zone because they tolerate hotter and drier climates than most other West Side conifers. Also called “mid-montane conifer forests” by some authors, a variety of other conifers including incense cedars, white firs, Douglas-firs, and sugar pines may now outnumber the ponderosas in mixed stands depending on fire history, elevation, and local conditions.
Before European settlement, these forests experienced frequent, low- to mid-intensity wildfires (primarily surface fires) that were a major factor influencing stand density, structure, and species composition. A policy of fire exclusion, or suppression, during the 20th century, along with the selective harvest of many large pines, has significantly changed fire behavior and led to an increase in fire severity and the number of infrequent but high-intensity, stand-destroying fires. In areas where fire has been prevented for many years, shade-tolerant white firs and incense cedars often outnumber the pines and oaks. In many ponderosa pine forests, kit-kit-dizze (a member of the rose family) covers the forest floor, and its pungent odor permeates the forest and clings to boots and clothing, earning it another name: “mountain misery.”
Large snags (i.e., greater than 24 inches diameter-at-breast-height) and decaying portions of living trees offer nesting cavities for Pileated Woodpeckers, Northern Flickers, and Western Screech-Owls. A variety of woodpeckers, Red-breasted Nuthatches, and Brown Creepers patrol the bark of conifers, while Warbling Vireos, Yellow-rumped Warblers, Black-headed Grosbeaks, and Western Tanagers make music from above. Near campgrounds and other developed areas, Steller’s Jays squawk and patrol their picnic tables, and Brewer’s Blackbirds strut across the pavement.
Pine-Oak Woodlands
North 2,000 to 6,500 feet; South 3,000 to 7,000 feet
Within the Lower Conifer zone, hardwood species like California black oaks, Pacific madrones, and bigleaf maples often intermingle with pines and other conifers. Black oaks, with dark trunks and bright green leaves, grow in patches mixed in with conifers—especially on open, rocky ridges and in forest clearings. These deciduous oaks turn gold in fall like the aspens, willows, and cottonwoods. The madrones and maples favor cool, wet drainages. Black oaks harbor hordes of caterpillars and flying insects that attract Nashville Warblers, Black-throated Gray Warblers, and Cassin’s Vireos to forage and sing. The high diversity of birds in these habitats is driven by an abundance of insects and nutrient-rich acorns. Accordingly, such acorn-consuming species as Western Scrub-Jays, Steller’s Jays, Acorn Woodpeckers, Mountain Quail, and Band-tailed Pigeons are common residents.
FIGURE 2 Lower Conifer zone
Oaks also provide nutritious sap that exudes from wounds in the bark caused by insects, tree falls, fire, and Red-breasted Sapsuckers. The sap provides feeding opportunities for the sapsuckers as well as for hummingbirds and warblers like Yellow-rumps and Orange-crowns. The high-protein seeds of many broadleaved trees are eaten by a long list of birds, including White-breasted and Red-breasted Nuthatches, Chestnut-backed and Mountain Chickadees, Dark-eyed Juncos, and Spotted Towhees.
UPPER CONIFER ZONE
Mixed Conifer Forests
North 5,500 to 7,500 feet; South 6,000 to 8,000 feet
As one proceeds up the West Side, ponderosa pines of the Lower Conifer zone blend into the cooler, moister, mixed conifer forests of the Upper Conifer zone. Mixtures of four or five species of conifers are typical in these forests, as the name of this habitat suggests. At places such as Crane Flat in Yosemite (Highway 120) and near the Giant Forest in Sequoia National Park, Jeffrey pines, with large cones and an aroma like vanilla rising from their bark, out-number ponderosas. Shade-tolerant white firs are often the most abundant trees, but usually incense cedars, Douglas-firs, sugar pines, and even a few red firs grow there, too. Black oaks reach this high but are fewer than farther down. Where the soil is rocky or wet, especially near meadows, lodgepole pines may grow in scattered stands. Giant sequoias, the world’s largest known living things, occur naturally only in the western Sierra, primarily in the Upper Conifer zone. A few grow as far north as Placer County, but most of the 75 groves are south of the Kings River and the largest, most majestic stands are in Sequoia National Park and Giant Sequoia National Monument.
Historically, many mixed conifer forests were comprised of large, thick-barked, fire-resistant trees, which were widely spaced with open understories. Fire suppression throughout the Sierra in the past century has greatly reduced the number and frequency of beneficial, low- to moderate-intensity fires that may have burned for weeks, or even months, cleansing the forest of the excess buildup of “ladder fuels” such as dead branches, small trees, and brush that fuel severe crown fires. There has also been a widespread increase in shade-tolerant tree species such as incense cedars and white firs within formerly pine-dominated stands.
In unburned and/or unlogged mixed conifer forests, huge conifers provide nesting habitat for Northern Goshawks, Spotted and Great Horned Owls, and foraging habitat and singing perches for Western Tanagers, Black-headed Grosbeaks, and Warbling Vireos. Hermit Warblers sound their buzzy songs from the deeper, shaded woods while White-headed and Pileated Wood-peckers call loudly from ancient snags. Golden-crowned Kinglets thrive in these forests, whispering high-pitched notes throughout the day.
FIGURE 3 Upper Conifer zone
Red Fir Forests
North 6,500 to 8,500 feet; South 7,000 to 9,000 feet
Red fir forests receive the heaviest Sierra snows. In these shady groves deep drifts often last long into summer, gradually releasing moisture into the soil. Small numbers of red firs grow on north slopes in the mixed conifer zone, but higher up their dark, silent columns reign supreme. Entire forests consist of only these trees, with rings of chartreuse lichen circling their trunks above the snow line. Often lodgepole and western white pines are mixed in, as are white firs at the lower edge of these forests. Particularly common in the northern and central Sierra, red firs grow only in limited areas farther south. At Porcupine Flat and Badger Pass in Yosemite and near Soda Springs on Interstate 80, impressive stands of red firs and lodgepole pines grow together. Lodgepole pines may form extensive stands in this zone, particularly in cold sites, around meadows, and on dry, rocky slopes. Heavy snows and deep forest litter prevent much growth of shrubs, grasses, or flowers; most birds in red fir forests search bark surfaces and sprays of conifer needles for food.
Red fir forests often seem lacking in birds, but if one listens carefully, rhythmic tapping of Williamson’s Sapsuckers may be heard. The characteristic sounds of Mountain Chicka-dees, Hermit Thrushes, Townsend’s Solitaires, Yellow-rumped Warblers, and Golden-crowned Kinglets echo through towering trees, and the complex, hyperspeed song of Pacific Wrens rises from the deep drainages. Flocks of Pine Siskins, Red Crossbills, or Evening Grosbeaks may fly overhead. Open areas with shrubs, wildflowers, and grasses draw Dark-eyed Juncos, Chipping Sparrows, and Cassin’s Finches that search the ground for insects and seeds. Some “edge” species such as Mountain Quail and “Mountain” White-crowned Sparrows use trees and shrubs for cover but feed in open areas nearby. At dusk, listen for the peents and booms of Common Nighthawks overhead and, as darkness comes, the incessant tooting of Northern Saw-whet Owls.
Mountain Chaparral
North 4,500 to 8,500 feet; South 5,000 to 9,500 feet
Brushfields of huckleberry oak, greenleaf manzanita, snowbrush, or chinquapin occupy steep, rocky slopes or forest clearings created by treefalls, logging, or fire. Especially prevalent on south-facing exposures, montane chaparral habitats may grow in impenetrable thickets but can be quite open on steep slopes or recently established sites. Some soil types are capable of only supporting chaparral. Although usually dry, these shrubfields are cooler than their foothill counterparts. Widespread above the foothills, montane chaparral habitats can be easily seen along Interstate 80 near Dutch Flat, Highway 120 west of Crane Flat in Yosemite, and on the slopes below Giant Forest in Sequoia National Park. Here the whistled melodies of Fox Sparrows may mingle confusingly with the similar songs of Green-tailed Towhees. Although they are often found in moist streamside habitats, Yellow Warblers and MacGillivray’s Warblers also nest in montane chaparral. Mountain Quail sneak through the underbrush and nest under this protective cover. At the edges where chaparral meets forest, you may find species such as Dusky Flycatchers and Western Wood-Pewees.
In some places, montane chaparral is an early stage of succession following a stand-replacing fire, destined to be gradually replaced by forest. In other spots, where the soils cannot support forest, the chaparral may represent a relatively permanent condition.
SUBALPINE ZONE
Lodgepole Pine Forests
North 7,500 to 9,000 feet; South 8,000 to 9,500 feet
Mountain lakes and springs spawn tiny streams that meander through meadow grasses and open stands of lodgepole pine. These pines also grow in dense groves that dominate the Subalpine zone, especially in the northern and central Sierra on both slopes, where they are sometimes joined by mountain hemlocks. Here and there, majestic specimens of western juniper occupy isolated, prominent cliffside locations. These trees, second only to the giant sequoia in longevity among Sierra trees, often bear the scars of numerous lightning strikes. Echo Summit (U.S. 50), Donner Summit (Interstate 80), and Tuolumne Meadows in Yosemite National Park have good examples of lodgepole pine forests. Hardy Mountain Chickadees reside in these forests year-round, moving along sprays of conifer needles and swinging down to inspect them from below. Dusky Flycatchers and Ruby-crowned Kinglets sound their familiar calls from forest edges and open ridge lines, while flocks of Red Crossbills and Pine Grosbeaks rove the treetops, even in winter. Hairy and Black-backed woodpeckers along with Williamson’s Sapsucker and Northern Flickers attack dead and dying lodgepole pines.
Lodgepoles growing at the edges of wet meadows and streams provide important nesting strata and cover for species closely associated with riparian habitats (this includes many migrating Neotropical songbirds such as flycatchers, vireos, warblers, and so on). The abundance of nesting and migratory songbirds draws predatory birds such as Cooper’s and Sharp-shinned Hawks, and Northern Goshawks. These hawks may nest in lodgepole pine forests but more frequently use them as hunting sites for ambushing prey, primarily birds but also rodents.
Subalpine Pine Forests
North 9,000 to 10,000 feet; South 9,500 to 11,500 feet
Backpackers head for these high forests where serrated ridges, perpendicular cliffs, and massive granite domes form spectacular vistas. On both sides of the Sierra, wind-sculpted whitebark pines grow with stunted lodgepoles on exposed ridges and north-facing slopes up to treeline. In the southern Sierra, erect stands of foxtail pine largely replace the gnarled whitebarks. The higher slopes of the Great Western Divide in Sequoia and Kings Canyon National Parks and the areas near Tioga Pass in Yosemite National Park have good examples of subalpine pine forests. Clark’s Nutcrackers and Pine Grosbeaks bound from tree to tree searching for pine nuts but dive for cover if the shadow of a Prairie Falcon skims by. Mountain Bluebirds, Dark-eyed Juncos, and “Mountain” White-crowned Sparrows forage in open, rocky areas. Here they are also joined by Common Ravens that prey on small birds and their eggs and nestlings and search for road-killed animals along high mountain roads.
FIGURE 4 Subalpine zone
ALPINE ZONE
Alpine Fell-Fields
North 8,500 to 10,800 feet; South 9,500 to >14,500 feet
The line of demarcation between the upper subalpine pine forests and treeless Alpine meadows is known as “timberline,” the point where trees cease to exist because of extremes in climate, shallow rocky soils, and high elevation. Here, freezing temperatures are possible any day of the year, and even the intense high-elevation sun does little to warm the cool, clear air. Life in these habitats is severe, and most plants are stunted by high winds, bitter cold, and shallow soils. Herbaceous plants dominate Alpine fell-fields, but stunted willows and other dwarf shrubs occur here as well. North of the Tahoe region, few peaks exceed 9,000 feet and alpine areas are limited to the summits of a few mountains, such as the Sierra Buttes in Sierra County, Castle Peak in Nevada County, and Granite Chief in Placer County. Farther south, many peaks exceed 13,000 feet, including Mount Whitney (14,496 feet), the highest mountain in the contiguous 48 states. Alpine environments are particularly extensive in Yosemite and Kings Canyon National Parks. Most Sierra Alpine fell-fields occur above the reach of highways, but a short hike from Carson Pass (Highway 88), Sonora Pass (Highway 108), or Tioga Pass (Highway 120) puts one amid the rugged cliffs, glacial cirques, and rock gardens of this zone.
In summer, wildflowers bloom profusely in Alpine fell-fields, and Dark-eyed Juncos and “Mountain” White-crowned Sparrows forage near shrubby willows. Gray-crowned Rosy- Finches feed on low turf or snow banks, and American Kestrels hover above. Mountain Bluebirds perch on boulders and dart out to snatch flying insects, the stunning blue of their plumage rivaling the alpine sky. American Pipits, Horned Larks, and Dark-eyed Juncos, as well as small mammals, attract raptors (especially during migration) such as Sharp-shinned and Cooper’s Hawks, Prairie Falcons, and Red-tailed Hawks. The summer flowering season coincides with an influx of hummingbirds that are either in migration or seeking relief from the summer drought and heat of the foothills. Rufous (in migration) and Calliope Hummingbirds can be abundant around particularly lush flower patches. Rock faces, boulder fields, and talus dominate much of the landscape in the Alpine zone, providing abundant habitat for Rock Wrens.
FIGURE 5 Alpine zone
EAST SIDE ZONE
Pine Forests
North 3,500 to 7,500 feet; South 3,000 to 8,500 feet
Growing in the Sierra rain shadow, pine forests of the East Side are generally more open and have smaller trees than the similar forests of the West Side. Easily seen along Highway 395, especially to the north of Mono Basin, they are dominated overwhelmingly by Jeffrey pines, but ponderosa pines are sometimes found as scattered individuals, or isolated pockets within larger Jeffrey pine stands, from Tahoe Basin north. Farther south, ponderosas are almost entirely replaced by Jeffrey pines, where higher elevations and associated colder temperatures combine to make soils drier. Some of the larger East Side basins, such as those surrounding Lake Tahoe and Mammoth Lakes, have extensive red fir and mixed conifer forests much like those on the West Side. Other tree species found on the East Side include western juniper, white fir, and lodgepole pine. East Side pine forests often have a dominant understory of Great Basin shrubs such as big sagebrush, bitterbrush, and rabbitbrush, along with numerous grasses and herbs. Some characteristic birds of these forests include Gray and Dusky Flycatchers, Pygmy Nuthatches, Clark’s Nutcrackers, and Red Crossbills.
Pinyon-Juniper Forests
North 3,500 to 8,500 feet; South 3,000 to 9,000 feet
At lower elevations of the East Side is an even drier habitat, pinyon-juniper forest, which is almost nonexistent on the West Side except at the southern end, where extensive stands occur in the drainages of the South Fork Kings River, the Kern River, and the South Fork Kern River. Highway 395 crosses through miles of this habitat where shrubby single-leaf pinyon pines grow in open stands, sometimes mingling with Utah junipers and Jeffrey pines interspersed between Great Basin shrubs like sagebrush, curl-leaf mountain mahogany, bitterbrush, and rabbitbrush. Bird species that tend to be more common in these forests than in pine forests are Pinyon Jays and Townsend’s Solitaires; Juniper Titmice occur in these habitats in the Mono Basin.
FIGURE 6 East Side zone
Great Basin Scrub
North 3,500 to 6,500 feet; South 3,000 to 7,000 feet
What may appear as a monotony of silvery-gray to olive-green shrubs in the lowlands of the East Side is often a floristically diverse assemblage of aromatic plants. Bitterbrush and sagebrush are the dominant shrubs, but a wide variety of other shrubs, perennial and annual forbs, and bunchgrasses may be found. Scattered emergent pines and large stands of curl-leaf mountain mahogany are also common. In large areas only the shrubs remain, forming the dominant habitat of the Great Basin. Sage-brush scrub also extends up to high elevations on dry hillsides of the East Side and locally west of the crest, as near Donner Summit. Driving the back roads through these scrubby habitats at dawn or dusk, one might flush a Greater Sage-Grouse, Common Nighthawk, or Common Poorwill, while birds that may be spotted any time of day are Say’s Phoebes, Gray Flycatchers, Sage Thrashers, and Vesper and Brewer’s Sparrows.
DESERT ZONE
Joshua Tree Woodlands
North none; South 2,000 to 7,000 feet
Joshua trees usually grow in widely scattered stands interspersed with a variety of evergreen and deciduous shrubs typical of Mojave desert scrub habitats. While Joshua trees sometimes grow in pure stands, more often there are a few singleleaf pinyon pines, Utah junipers, or Mojave yuccas somewhere in the vicinity. Joshua trees are generally found at moderate elevations in broad valleys with deep soils situated between mountains and mesas. Bird life in Joshua tree woodlands is similar to desert scrub habitats, but Joshua trees offer lookout posts, song perches for a few species such as Ladder-backed Woodpeckers, Cactus Wrens, and Scott’s Orioles that are not found elsewhere in the Sierra region. Joshua tree woodlands are easily observed along Highway 178 on both sides of Walker Pass in Kern County.
FIGURE 7 Desert zone
Desert Scrub and Washes
North none; South 2,000 to 7,000 feet
In the Sierra, desert scrub habitats are usually dominated by creosote bushes standing up to six feet high with considerable open ground in between. Creosote bushes are often surrounded by other desert plants like catclaw acacia, desert agave, burrowbrush, rabbitbrush, teddybear chollas, or beavertail pricklypear cactus. These habitats receive little rainfall with cold, dry winters and hot, dry summers. In the Sierra region, these habitats can only be found in Inyo and Kern Counties, where they can be accessed easily from Highways 14, 58, 178, and 395. Small mammals, birds, and reptiles provide prey for Red-tailed Hawks, Prairie Falcons, and Loggerhead Shrikes. Plants in desert wash habitats tend to be taller than in surrounding desert scrub habitats, and some typical species include blue paloverde, desert ironwood, smoketree, catclaw acacia, mesquite, and the invasive tamarisk. A stroll down a desert wash might offer views of a Greater Roadrunner, Phainopepla, or a flock of Black-throated Sparrows.
SPECIAL HABITATS
The habitats described in this section are of limited extent in the Sierra but provide key resources for birds. Because of their importance and because each occurs across a wide range of ecological zones, they are described separately here.
Riparian Forests
Only small fragments remain of the shady jungles of sycamores, cottonwoods, and willows that once flourished along rivers of the Sierra foothills. Most were cleared long ago for lumber, firewood, and agriculture or inundated by large reservoirs. By far the largest and most impressive remaining lowland riparian forest in the Sierra is along the South Fork Kern River, upstream from Lake Isabella. This riparian oasis is more than a mile wide, includes more than 3,000 acres, and extends for miles—it is now protected by the California Department of Fish and Game, the U.S. Forest Service, and Audubon California. The South Fork Kern River riparian forests support breeding populations of a number of special status bird species that breed nowhere else in the Sierra, such as Yellow-billed Cuckoos, “Southwestern” Willow Flycatchers, Brown-crested Flycatchers, Vermilion Flycatchers, and Summer Tanagers.
FIGURE 8 Riparian forest (photograph by Phil Robertson)
Overall, remaining lowland riparian forests along West Side rivers and streams support a higher density and diversity of breeding and migratory birds than any other Sierra habitat. Numbers of migratory birds in riparian areas can be more than 10 times greater than found in the surrounding uplands. Draped in wild grapes, berry vines, or poison oak, these lush groves offer moisture and shade during the hot summers. Breeding birds like Yellow Warblers, Yellow-breasted Chats, Warbling Vireos, House Wrens, and Black-headed Grosbeaks sing above the constant din of humming insects, while Downy and Nuttall’s Woodpeckers drill on branches and flake off bark. Other typical Sierra riparian birds include Black Phoebes, Pacific-slope Flycatchers, Ash-throated Flycatchers, House Wrens, Orange-crowned Warblers, Spotted Towhees, Song Sparrows, and House Finches.
In the Lower and Upper Conifer zones, riparian forests mostly become narrow, discontinuous corridors of dogwood, black cottonwoods, and aspens or, more typically, tall willows or alders. In the Subalpine zone, shrubby willows and alders form a narrow and patchy border along most streams. Narrow stands of moisture- loving deciduous trees also border some ponds and lakes throughout the high Sierra. In all these ecological zones, deciduous trees often replace conifers along streams, especially in steep terrain. Song Sparrows and Yellow and Wilson’s Warblers breed in these broad-leaved trees, and migrant vireos, warblers, sparrows, finches, and tanagers flock to them in late summer and fall. Turbulent mountain streams are home to Common Mergansers, American Dippers, and rarely Harlequin Ducks. Nearby sandbars may harbor nesting Spotted Sandpipers or perhaps a family of Killdeer.
Aspens commonly form large broad-leaved woodlands in the high mountain regions and dominate riparian areas along the entire East Side, where they are joined by cottonwoods and willows. The pale, light green leaves or yellow autumn hues and white bark provide a dramatic contrast to the various coniferous forest communities that span their range in the Sierra. Aspen woodlands provide important breeding, resting, and foraging habitat for a diverse array of birds that eat the buds, flowers, seeds, and catkins of quaking aspens and supply a yearlong food source for Sooty Grouse. Typical nesting birds include Red-breasted Sapsuckers, Hairy Woodpeckers, Northern Flickers, Warbling Vireos, Tree and Violet-green Swallows, MacGillivray’s and Yellow Warblers, and Song Sparrows. Breeding raptors may include Great Horned Owls, Cooper’s Hawks, and Northern Goshawks.
FIGURE 9 Mountain meadows
Mountain Meadows
Mountain meadows usually begin as lakes that are gradually filled with sediment from the surrounding uplands and may someday become forests. Grasses, sedges, and rushes share the moist central portions with wild onions, corn lilies, shooting stars, and countless other wildflowers, while young trees gradually colonize the edges. These meadows are most numerous and extensive in the glaciated terrain of the Subalpine zone but are also scattered throughout the Lower and Upper Conifer zones of the Sierra. They range in size from small forest clearings to wide expanses such as Tuolumne Meadows in Yosemite National Park, the largest example of these high-country flower gardens in the Sierra. Perazzo Meadow in Sierra County is another spectacular, and recently protected, mountain meadow paradise. One can walk for miles in any direction through these vast expanses, encountering Calliope Hummingbirds, Golden Eagles, Prairie Falcons, American Kestrels, Willow Flycatchers, Dark-eyed Juncos, Chipping Sparrows, and Mountain Bluebirds along the way. Unfortunately, many of the Sierra’s largest and most spectacular meadows, such as Hetch Hetchy Valley in Yosemite National Park, are now buried beneath the waters of human-made reservoirs.
Growths of shrubby willows tracing the main stream courses in wet mountain meadows harbor birds such as Willow Flycatchers, Lincoln’s Sparrows, and MacGillivray’s Warblers. Abundant mosquitoes, dragonflies, and butterflies dance in the air while Western Wood- Pewees and Olive-sided Flycatchers perched at meadow’s edge scan for these and other insects. Wet meadows stay green all summer, while dry grassy sites atop domes and ridges usually turn brown and go to seed by the end of August. The margins of many Sierra meadows are ringed by aspens or cottonwoods that display a brilliant gold when framed against a blue October sky. Whether rimmed with broad-leaved trees or ranks of conifers, forest-meadow edges attract birds like Western Bluebirds, Yellow-rumped Warblers, Chipping Sparrows, Dark-eyed Juncos, and Purple Finches that forage among meadow plants for insects and seeds and take to the trees for cover.
The edges of forests and mountain meadows are among the most rewarding for birdwatchers. During the night, cold air flows down into meadow depressions and by dawn these areas become significantly colder than nearby forests. Like humans, birds seek warmth at dawn and usually flock to the sunny sides of mountain meadows. Sandhill Cranes and Wilson’s Phalaropes sometimes nest in wet meadows on the East Side. Dense forests near meadow edges provide nesting habitat for raptors such as Northern Goshawks and Spotted Owls. Great Gray Owls primarily search for prey in these mountain meadows.
FIGURE 10 Freshwater marshes
Freshwater Marshes
Freshwater marshes are distinguished from deep water aquatic habitats and wet meadows or grassland habitats by the presence of rushes, sedges, or tall, erect, grasslike plants such as tules and cattails that are rooted in soils that are permanently or seasonally flooded or inundated. Marshes can occur in basins or depressions at all elevations, aspects, and exposures, but they are most common on level to gently rolling topography below about 4,000 feet but can be found above 8,000 feet in the southern Sierra. On the West Side, freshwater marshes are mostly confined to the shallow edges of reservoirs and ponds; the largest ones are at Lake Almanor in the north and Lake Isabella in the south. On the East Side, sizable marshes can be found at Honey Lake, Sierra Valley, and Carson Valley, at such large lakes as Bridgeport Reservoir, Lake Tahoe, and surrounding Mono Lake. Freshwater marshes also occur as fringes around reservoirs such as Lake Crowley where the slopes are gentle enough to create a rim of shallow water. On slow-moving meadow streams, freshwater marshes can occur as narrow bands over long distances.
Freshwater marshes teem with bird life. Where shorelines are clogged by tules, cattails, or rushes, these aquatic habitats harbor Canada Geese, Mallards, Cinnamon Teal, Virginia Rails, Soras, American Coots, Common Gallinules, Wilson’s Snipe, Marsh Wrens, Common Yellowthroats, and throngs of Red-winged Blackbirds, while Great Blue Herons stand like statues in the shallows.
Reservoirs, Lakes, and Ponds
Most Sierra “lakes” are actually artificial reservoirs. More than 150 reservoirs exist on West Side rivers and creeks, and the largest of these (more than 5,000 surface acres) are Lake Almanor and Lake Oroville (Feather River), New Melones Lake (Stanislaus River), Don Pedro Reservoir (Tuolumne River), Lake McClure (Merced River), Millerton Lake (San Joaquin River), Pine Flat Lake (Kings River), Lake Success (Tule River), and Lake Isabella (Kern River). On the East Side, examples of large reservoirs include Lake Davis (Plumas County), Stampede (Sierra County), Prosser Creek and Boca (Nevada County), Topaz Lake (Douglas County, Nevada), Bridgeport Reservoir, and Crowley Lake (Mono County).
FIGURE 11 Reservoirs, lakes, and ponds (Mono Lake)
Fish-eating birds such as Ospreys and Bald Eagles patrol the surfaces of these reservoirs, while Double-crested Cormorants, American White Pelicans, Western and Clark’s Grebes, Common Loons, and Common Mergansers dot the surface and dive for similar prey. A wide diversity of waterfowl, shorebirds, and other aquatic birds can be found in natural East Side lakes and wetlands such as Honey Lake and Lake Tahoe. Mono Lake hosts almost a million Eared Grebes and thousands of Wilson’s and Red-necked Phalaropes in fall migration as well as the largest California Gull breeding colony in California.
Smaller lakes, ponds, and sewage treatment plants attract ducks like American Wigeon, Northern Shovelers, Ring-necked Ducks, Buffleheads, Hooded Mergansers, and Ruddy Ducks as well as California Gulls and flocks of shorebirds where mudflats are exposed. However, because most Sierra rivers flow through steep-sided canyons, extensive mudflats are scarce, but they do occur around reservoirs, lakes, and ponds with gentle slopes where ducks like Northern Shovelers, Gadwalls, American Wigeon, Northern Pintails, and Green-winged and Cinnamon Teal dabble in the shallows.
Although unequaled in beauty, clear lakes in the Alpine and Subalpine zones offer little food for birds. Probably the most common visitors to these waters are California Gulls traveling to and from their Great Basin breeding grounds. Spotted Sandpipers and American Dippers may patrol their margins for aquatic insects but never in large numbers.
Old Growth Forests
If a forest can avoid severe fire and the chainsaw for a couple of centuries, it may attain a state commonly known as “old growth.” This represents a “climax” stage and can, under the right conditions, last for many more centuries with little change in structure or species composition. Small, localized stands of old growth forests occur in the Lower Conifer zone, but most of the remaining old growth in the Sierra exists in the Upper Conifer zone; the most extensive stands are in Yosemite and Sequoia National Parks. The best estimate is that at least 67 percent of Sierra mixed conifer forests were in this condition at the time of European settlement of California. Today less than 12 percent remains, much of it in isolated fragments. Old growth forests include huge trees, a wide variety of tree sizes and species, very large snags, and a relatively sparse understory with the fallen boles of ancient giants scattered about the forest floor. They tend to be cool, dark, and quiet. Although these forests harbor relatively few birds compared to some other Sierra habitats, they are by far the most productive habitats for some species, such as Spotted Owls and Northern Goshawks. While no bird species uses old growth exclusively, some species, such as Brown Creepers, Pileated Woodpeckers, and Great Gray Owls, are strongly associated with these ancient forests.
One could think of old growth as a final stage. However, from nature’s perspective, it is just part of a cycle of succession. Imagine an old growth forest that finally meets a combination of conditions that allows a severe fire to reach the crowns of the trees and kills all or nearly all of them. Within hours of the fire’s end, bark beetles from as far away as 100 miles have sensed the conditions needed to reproduce. They arrive and lay the eggs of their next generation in the snags. Once they hatch and larvae begin to grow and consume the dead wood, a woodpecker feast of magnificent proportions begins. By the following spring, the ground is ablaze in a new fire of wildflowers of stunning variety and abundance. Within a few years a healthy growth of shrubs appears and along with them, the suite of bird species that needs this mountain chaparral. At this point the snags are becoming ideal homes for cavity-nesting birds. Gradually, sun-loving trees begin to grow among the shrubs. Once those trees attain the size to provide shade, the shrubs begin to disappear and shade-adapted trees begin to take hold, destined to overtop and shade out the earlier tree species. At each stage a different suite of birds finds their ideal conditions. Given enough time, this forest may once again achieve old growth status.
Recent Burns
Terms like “tragic” and “devastating” are often linked to large forest fires in media reports. However, this judgment misses the point that fire, even intense stand-replacing fire, is a crucially important part of the Sierra ecosystem and is necessary to maintain the biodiversity of the region. Birders know well that time spent at the site of a fairly recent fire can be the most exciting and productive part of a day in the field. At lower elevations on the West Side, Rufous-crowned Sparrows are among the first birds to take advantage of these newly open areas. Lazuli Buntings will appear in large numbers within the first few years. Blue-gray Gnatcatchers, California Thrashers, Bewick’s Wrens, and an amazing variety of sparrows all favor these areas. Where large fire-killed snags remain, Black-backed Woodpeckers may appear quickly to take advantage of the insects that infest these trees. A host of other cavity-nesting birds—like Hairy Woodpeckers, Northern Flickers, Mountain Chickadees, and Mountain and Western Bluebirds—soon occupy these areas.
Olive-sided Flycatchers sally out from the tops of highest snags to catch insects on the wing. These burned areas will generally support a higher diversity of birds and a different suite of species than the surrounding forest. Thus the mosaic of habitats created by fires of varying intensity over varying periods is a key force driving the Sierra’s remarkable diversity of birdlife.
Rocks and Cliffs
In the northern Sierra, ancient volcanoes spewed molten lava across the landscape, but the central and southern Sierra have a different geologic history and display vast expanses of glacier-polished granitic cliffs, domes, and scattered boulders. Some of the earth’s finest rock work graces the canyons of the Merced and Tuolumne Rivers in Yosemite and the high country of Sequoia and Kings Canyon National Parks. Rock crevices and ledges high on steep canyon walls provide nesting sites for swifts, Golden Eagles and Prairie and (more and more frequently) Peregrine Falcons. Rock Wrens, Rosy-Finches, and the occasional introduced White-tailed Ptarmigan scuttle confidently across alpine talus slopes, and Canyon Wrens inhabit jumbles of boulders in river gorges.
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.
