Nature's Bounty: A Rich Diversity of Wildlife
Two hundred and fifty years ago, many fresh-water creeks wove through the peninsula, eventually feeding into the Bay and the Pacific Ocean. Today only six above-ground creeks remain in the city, and one of them is Islais Creek in Glen Canyon Park. The creek is named for the Ohlone word "islay," meaning cherry, and refers to the wild cherry trees that grow in the park and throughout the creek's watershed. Although urban development has greatly altered the creek's natural flow, its year-round water and surrounding vegetation continue to function as an important habitat area for animals, including coyotes, resident and migratory birds, and insects.
The creek is also potential habitat for the San Francisco forktail damselfly, Ischnura gemina.This native arthropod is a candidate for classification as a threatened or endangered species by the U.S. Fish and Wildlife Service.
Glen Canyon Park's steep slopes also support thriving grassland and coastal scrub communities, which suggest how much of the northern San Francisco peninsula may have looked before it was settled extensively. Geologically, the rocky chert outcrops add another facet of diversity to the variety of habitats in the park. The western slopes of the park are home to eucalyptus trees, while native lupine species flourish in the eastern slope's grassland community. Glen Canyon Park also hosts a variety of animal life, from the Red-tailed Hawks, Buteo jamaicensis, that soar above the rock outcrops to the coyotes, Canis latrans, that have been sighted hunting in the grassland.
Glen Park is one of the city's 31 significant natural resources areas managed by the San Francisco Recreation and Park Department. In addition to its outstanding views, the park boasts some of the city's largest and most accessible rock outcrops. The park also encompasses Islais Creek, one of four remaining free-flowing creeks in the city. Islais Creek supports a diverse streamside community of thriving willow trees and prehistoric horsetail, and serves as an important resting place for migratory birds. Each year, birds traveling from as far away as Alaska and Tierra del Fuego in Chile depend on Islais Creek as a stopping point as they cross the Golden Gate.
Naturalists enjoying Glen Canyon's boardwalk (Photo by Margo Bors)
The Great-horned Owl, Bubo virginianus is more often heard than seen. This widespread owl inhabits Glen Canyon's mature woodlands. By day Great-horned Owls try to stay hidden, usually roosting high up in large trees and using their brown tones to camouflage with bark. By night this large owl flies from perch to perch and can catch its food in pitch darkness. Favorite prey of Great-horned Owls in Glen Canyon include rodents, roosting birds and even skunks!
Great Horned Owl (Photo by David Marotta)
Glen Canyon is home to Islais Creek, one of six remaining above-ground creeks in San Francisco. These include Mission Creek which still flows into the Bay at China Basin, Grey Fox Creek in McLaren Park, and three in the Presidio called Lobos, Dragonfly, and Tennessee Hollow Creeks. Water-loving plants such as willow trees and other deciduous trees and shrubs dominate this plant community, which also consists of currant, horsetail, seep monkey flower, and red columbine.
Columbine, Aquilegia Formosa (Photo by Christopher Campbell)
The coyote brush, Baccharis pilularis, is another unique member of the coastal scrub community. This native bush provides shelter for birds and other small animals and food for insects, but it does not rely on animals for pollination or seed dispersal. The coyote brush is dioecous, which means that its male and female parts occur on separate plants, a relatively uncommon condition in the plant kingdom. This separation of the sexes on to different plants prohibits self-fertilization it the species. Wind carries pollen from the male plant to the female plant, which produces fluffy seeds that can be seen in the fall.
Over 250 species of insects are associated with coyote bush. (Photo by Margo Bors)