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.