Wildlife Habitats in GGNRA
From the northernmost areas near Tomales Bay and Olema Valley, around the Golden Gate, and to the southernmost areas of Sweeny Ridge and Phleger Estate, the natural communities of GGNRA make up a diverse landscape that supports a large number of wildlife habitats, both marine and land-based.
GGNRA is home to many wildlife species and is one of the richest biological preserves. The diversity of habitats extend from the Pacific Ocean to the coastline, sea cliffs to sand dunes, mud flats to salt marshes, chaparral and coastal scrub to grasslands, and redwood forests to oak woodlands. Wildlife species may cross from one community or habitat to other adjacent communities and habitats - particularly bird and mammal species.
Marine and Intertidal Habitats
GGNRA has more than 24 miles of ocean and bay coastline. The ocean and intertidal habitats near Slide Ranch, Muir Beach, Pirates Cove, Tennessee Cove, Kirby Cove, Bird Island, and Fort point support diverse and complex ecosystems, including numerous invertebrate species and vertebrate species. Marine invertebrate species include a variety of sponges, jellyfish, sea anemones, mollusks (abalone, mussels and clams), crustaceans (barnacles, crab, and shrimp), and echinoderms (sea stars and sea urchins), and other class and species.
Marine vertebrate species include marine mammals (sea lions, seals, and whales) and numerous fish species. California gray whales, the federally endangered humpback whales, and harbor porpoises pass through nearshore waters, and occasionally young whales wander into San Francisco Bay. The southern sea otter, a federally threatened species, is infrequently seen in marine waters offshore from GGNRA, but populations are increasing at the Fitzgerald Marine Reserve in San Mateo County. The sea otter's population has been declining for unknown cause, but may be due to marine pollution, disease, and commercial fisheries.
Beaches, Sea Cliffs, and Coastal Wetland Habitats
The marine environment supports much of the wildlife in the adjacent sea cliffs, sand dunes, and coastal wetlands. Sandy beaches, lagoons and estuaries in the park, including Tomales Bay, Bolinas Lagoon, Stinson Beach, Muir Beach, Big Lagoon, Rodeo Lagoon, the Golden Gate, Crissy Field, and Ocean Beach provide important habitat for migrating and wintering water and shorebirds.
Sandy beach and dune habitats within GGNRA occur at Lands End, Baker Beach, Ocean Beach and Fort Funston. Ocean Beach has been an important habitat for the federally threatened western snowy plover, but due to habitat loss, their numbers are shrinking.
Along the sea cliffs of the Marin Headlands to the north and Fort Funston to the south, sea birds such as the western gull, the pelagic cormorant, double-crested cormorant, California gull, Brandt's cormorant, and the black swift, among many other birds, find shelter for roosting, breeding, and nesting. The cliffs are also close to their food source, which consists primarily of fish. Bank swallow colonies at Fort Funston are declining as they have been threatened by competitors, predators, and erosion caused by coastal storms and human impact.
Estuarine communities such as Tomales Bay, Bolinas Lagoon and Rodeo Lagoon are populated by several species of birds - including the great blue heron, the endangered brown pelican, white pelican, canvasback duck, greater scaup, lesser scaup, red-breasted merganser, ruddy duck, least tern, Caspian tern, long-billed curlew, black-bellied plover, willets, short-billed dowitchers, greater yellowlegs, whimbrels, dunlin, western sandpipers and several species of egrets, cormorants, and gulls. The endangered brown pelicans bathe, feed, and roost in Rodeo Lagoon, so the preservation of this habitat is critical to their survival.
Other wildlife in the estuarine community includes fish like the endangered tidewater goby and the federally threatened steelhead trout, marine mammals such as seals and seal lions, and small mammals such as the federally endangered salt marsh harvest mouse.
Isolated coastal rocks, beaches, and lagoon sand flats, including Point Bonita Cove at Marin Headlands, Bolinas Lagoon, and Tomales Bay, are haul-outs for harbor seals and California sea lions. The Stellar sea lion, a federally threatened species, historically were seen on Seal Rocks in San Francisco and the Farallon Islands, but sightings are now rare.
Additionally, countless numbers of marine invertebrate species live in estuarine communities.
Habitats in the Coastal Hills, Ridges, and Valleys
From the coastal bluffs to interior grassy knolls and valleys, many of the GGNRA parks traverse several types of natural communities and habitats including chaparral, coastal scrub, coniferous forests (including redwood groves), mixed evergreen forests, coastal grassland, and oak woodlands. Together, they support a diversity of wildlife.
The mosaic of flora and fauna communities and habitats created by the rolling coastal hills, ridges, and valleys occur in Olema Valley and Bolinas Ridge to the north, Tennessee Valley, Muir Woods, Marin Headlands, and Milagra Ridge and Sweeny Ridge to the south.
Coastal Bluffs
The Marin Headlands, located just north and west of the Golden Gate Bridge, is one of the best places to view migrating raptors in the fall. The Golden Gate Raptor Observatory, a project of the Golden Gate National Parks Association and the National Park Service, conducts educational talks and demonstrations on Hawk Hill, which is located just above the Golden Gate Bridge at the top of Conzelman Road. Species of raptors observed on Hawk Hill include the red-tailed hawk, Cooper's hawk, sharp-shinned hawk, turkey vulture, osprey, red-shouldered hawk white-tailed kite, northern harrier, American kestrel, prairie falcon, broad-winged hawk, and the peregrine falcon, among others. Many of the raptors can also be viewed from Sweeny Ridge in San Mateo County, as they migrate south.
In the coastal scrub and chaparral communities, species of wildlife include: mammals such as the California mouse, Merriam's chipmunk, striped skunk; reptiles like the racer snake, southern alligator lizard, and the endangered garter snake (may occur at Milagra Ridge); birds such as several owl species, wrentits, scrub jays, California quail, and bushtits.
At least 44 species of butterflies occur in the Marin Headlands and 34 species occur at Milagra Ridge. The federally endangered Mission blue butterfly lives in the Marin Headlands, Milagra Ridge, and Sweeny Ridge. The endangered San Bruno elfin occurs at Milagra Ridge, where it inhabits rocky outcrops.
Redwood Forests
Within GGNRA, the redwood forests, typically found on the north-facing slopes of Marin County hillsides, support an abundance of wildlife in the old growth trees, streams and creeks, undergrowth, and soil.
The redwood forest of Muir Woods is habitat for at least 69 bird species including the Pacific-slope flycatcher, winter wren, golden-crowned kinglet, chestnut-backed chickadee, Stellar jay, rufous hummingbird, Allen's hummingbird, Vaux's swift, hairy woodpecker, and several species of owls including the northern spotted owl.
The moist areas and creeks within the redwood forest are habitat for amphibian species including frogs, salamanders, and newts, reptiles such as western pond turtles, and fish species such as rainbow trout.
Mammals
in the redwood forest include Merriam's chipmunk, Trowbridge's shrew,
Sonoma chipmunk, western gray squirrel, opossum, black-tailed deer,
dusky-footed woodrat, striped and spotted skunks, coyote, bobcat, long-tailed
weasel, mountain lion, river otter, and
several species of bats such as Townsend's big-eared bat, a federal
species of concern. At least 30 species of mammals inhabit Muir Woods.
The unusual looking banana slug, an invertebrate species in the Gastropod Class, is common in the undergrowth of Muir Woods. These and other invertebrates keep the soil healthy so that the other habitats above can thrive.
Oak-Pine Woodlands and Grasslands
Oak-pine woodland and grassland communities occur in the valleys between ridges throughout the coastal hills of GGNRA. In GGNRA, these communities occur in Olema Valley, Tennessee Valley, and parts of the Marin Headlands. These areas - and the adjacent coastal scrub and grassland areas - support a variety of mammals such as the bobcat, mountain lion, coyote, gray fox, mule deer, raccoon, striped skunk, black-tailed jack and brush rabbits, pocket gopher, California vole, broad-footed mole, western harvest mouse, deer mouse, and occasionally badgers.
Common bird species to these communities are the scrub jay, western bluebird, black-headed grosbeak, acorn woodpecker, ruby-crowned kinglet, blue-gray gnatcatcher, warbling, vireo, orange-crowned warbler, Hutton's vireo, and yellow-rumped warbler, and several species of hawks and other raptors. Hawks use oak trees for perching and probe for prey.
Island Habitats
Alcatraz Island receives 1.5 million visitors a year; many come to tour the historic prison within GGNRA. There is much more to Alcatraz Island than this popular tourist attraction. Alcatraz is a significant bird refuge and important nesting area for several species of birds, including the endangered Brown Pelican and other federally endangered or threatened species.
Other species of birds supported by the island include: the white pelican; pigeon guillemots; Brandt's, double-crested, and pelagic cormorant; western and Heerman's gulls; black-crowned night heron; pacific slope flycatcher; winter wren; golden-crowned kinglet; chestnut-backed chickadee; band-tailed pigeon; Allen's hummingbird; Canada geese; mallards; common mergansers; song sparrows; white-crowned sparrows; common ravens; black oystercatcher; and great and snowy egrets.
One indigenous amphibian, the California Slender Salamander, and one indigenous mammal, the deer mouse, also inhabit Alcatraz Island.
"Urban Island" Habitats
Unique to GGNRA, and other nature preserves that border large urban areas, is the concept of "urban island" habitats. Within GGNRA, the Presidio is a quintessential example of an urban island. Urban islands have new issues, challenges, and impacts, which require specialized resource management and wildlife conservation. The habitats of the Presidio vary from indigenous and exotic forests, coastal scrub and grasslands, to riparian habitats.
Common and widespread species, such as the California slender salamander, alligator lizard, California vole, and western harvest mice occupy a wide range of habitats and appear to have stable populations inside the Presidio. However, the isolated conditions of an urban island reserve may not be able to support the Coast Range newt, western skink, sharp-tailed snake, Pacific ring-necked snake, Santa Cruz garter snake, and the gray fox in the longer term.
Most vertebrate species in the Presidio are birds, including spring and fall migrants or winter visitors. Approximately 60 bird species may be nesting in the Presidio. The forests in the Presidio are important habitat for the olive-sided flycatcher, vireos, warblers, tangers, grosbeaks, California quail, western screech owl, wrentit, Hutton's vireo, and the hooded oriole.
The Presidio is home to only a few mammal species, primarily bats. At least six species of bats have been detected by their sounds. The bats prefer the shelter of the historic World War II structures found at the Presidio.
References:
Bakker, Elna S. 1984. An Island Called California. Berkeley and Los Angeles: University of California Press.
Golden Gate National Recreation Area, National Park Service, United States Department of the Interior. 1999. Natural Resources Section of the Resources Managment Plan: Golden Gate National Recreation Area.
