Wildlife of Riparian and Wetland Areas

Although riparian vegetation makes up just a small fraction of the total land area in California, wildlife seek food and shelter there more often than any other habitat type (FISRWG 1998). Over 225 species of birds, mammals, reptiles, and amphibians depend on stream corridors for food, water, shade, shelter, nesting, and migratory pathways (RHJV 2000). Streams and stream corridors act as the circulatory system of the Earth's surface, sustaining the life of many species.

Human activities such as flood control, agriculture, sand and gravel extraction, transportation routes, and urbanization have contributed to the loss of over 95 percent of the riparian habitat present in California in the mid-1800s (RHJV 2000). The sensitivity of animal communities to vegetative communities is well-recognized (FISRWG 1998), and with the loss of riparian habitat there has been a corresponding reduction in associated animal populations. Consequently, many riparian-dependant animal species are now listed as species of concern, threatened, or endangered. In San Mateo and Santa Cruz Counties, there are 13 special status species that occur within riparian or wetland habitats.

To get an accurate estimate of the wildlife species that depend on a single watershed or stream requires an in-depth biological survey involving many hours of careful observation in different locations along the stream corridor during both day and night and in all seasons of the year. Unfortunately, surveys with this level of detail can take more time and money than is usually available, but it is possible to use prior research to predict the species present based on the habitat within a given area. The California Department of Fish and Game (CDFG) has developed a computer database program called the California Wildlife Habitat Relationships (CWHR, Version 8.0) that includes all of the known terrestrial vertebrate taxa in California and their associated habitats (visit the CWHR Web site for more information). This database consists of predictive models that can produce several types of reports listing wildlife species that are expected to occur in a given location and set of habitat conditions. According to the database, there are approximately 200 terrestrial vertebrate species that depend on the riparian and wetland habitats (riverine, valley foothill riparian, montane riparian, estuarine, saline emergent wetland, freshwater emergent wetland, and redwood) found in San Mateo and Santa Cruz Counties. There are also many fish species in addition to salmonids that make their home in riparian streams of these areas. Common species of the follwing animals are discussed here:

• mammals
• birds
• amphibians and reptiles (herpetofauna)
• fish

Species Profile: Salt Marsh Harvest Mouse

Mammals

Of the 502 recent native species and subspecies of land mammals in California (Hall 1981), approximately 25 percent (133 taxa) are limited to or largely dependent upon riparian and other wetland communities (Williams and Kilburn 1984). No other general type of habitat is as important to mammals as riparian and wetland communities. The combination of cover, water and food resources makes riparian habitat desirable for many species that use multiple habitat types including mule deer, coyote, and bobcats. Other mammals – such as ringtail, common muskrat, and raccoon – are dependant upon riparian habitat for at least part of their range (FISRWG 1998). Riparian habitat also provides dense cover for roosts, water, and abundant insect populations required by many bat species. The watersheds in San Mateo and Santa Cruz Counties support twelve bat species – all insectivorous – which help to control the mosquito and other biting insect populations. Populations of mammalian species dependent upon freshwater and tidal riparian wetland communities have dramatically declined in nearly every region within California (Williams and Kilburn 1984). As riparian corridor width is reduced and removed, the habitat becomes fragmented and no longer provides a migration corridor. This reduced habitat cannot support the number or diversity of mammal species that is supported by a healthy system. For a complete list of results from the CWHR database, see the Mammals of San Mateo and Santa Cruz Counties Table.

Birds

Species Profile: Marbled Murrelet

Riparian zones have been identified as the most important habitats for landbird species in California (RHJV 2000). The structural complexity and species diversity of riparian corridors provides habitat required for nesting, sheltering, and foraging. Insect production is high within the riparian corridor, providing a rich food source for insectivores such as vireos, warblers, swallows, wrens, and flycatchers. Riparian forest trees such as box elder, big-leaf maple, and birch are highly productive, producing food resources for seed feeders such as grosbeak, finches, and sparrows. Migrating species such as the warbling vireo – a neo-tropic species that travels from Central America to nesting areas along California's Central Coast – use riparian corridors to rest and feed during their annual migration. Additionally, coastal riparian corridors are the nesting destination for some bird species. Both resident and migrant species nest within riparian vegetation. Cavity-nesting species such as owls, woodpeckers, and ducks may require a special habitat component – standing dead trees (snags) – to provide appropriate nesting sites. Although snags may be considered unsightly and dangerous, this dead wood creates a unique habitat necessary for nesting, while providing a rich food source for insectivores. Soquel Demonstration Forest is currently examining the effectiveness of creating snags within the Soquel Creek watershed to create habitat. Finally, water resources within riparian systems provide habitat and feeding opportunities for piscivorous and aquatic feeding bird species, such as osprey, herons, and ducks. For a complete list of results from the CWHR database, see the Birds of San Mateo and Santa Cruz Counties Table.

Species Profile: Long-toed Salamander

Species Profile: San Francisco Garter Snake

Amphibians and Reptiles

In northern California, approximately 50 percent of both reptiles and amphibians prefer riparian or aquatic habitats (Raedeke et al. 1988). Nearly all amphibians (salamanders, toads, and frogs) depend on aquatic habitat for reproduction and over wintering (FISRWG 1998). Many reptiles are functionally tied to riparian and wetland areas and some are indicators of riparian ecosystem health. While less restricted by the presence of water, many reptiles are found primarily in stream corridors and riparian habitats. For a complete list of results from the CWHR database, see the Amphibians of San Mateo and Santa Cruz Counties Table and Reptiles of San Mateo and Santa Cruz Counties Table.

Fish

While riparian habitat supports a wide variety of animals, the streams also provide important habitat. The stream environment has many habitat types that appeal to a variety of fish such as deep pools for resting, shallow riffles for foraging, and lagoon and estuary areas for nursery habitat.

Unlike salmonids and other anadromous fishes, which can alter their physiology to live in both salt and fresh water during certain life stages, most fish species are adapted to a single habitat type. Freshwater habitats support different fish species than are observed in brackish and saltwater estuary habitats. Common native freshwater fish species in coastal streams of San Mateo and Santa Cruz include prickly sculpin (Cottus asper), coastrange sculpin (Cottus aleuticus), Sacramento sucker (Catostomus occidentalis) and threespine stickleback (Gasterosteus aculeatus) – a freshwater or anadromous species (Conrad et al. 2003, SH&G et al. 2002).

Salmonids, such as steelhead trout (Oncorhynchus mykiss), spawn in many coastal streams in San Mateo and Santa Cruz Counties, while coho salmon (O. kisutch) maintain populations in San Vicente, Waddell, Gazos, and Scott Creeks (see the State of Fisheries section for more information). Pacific lamprey (Lampetra tridentate) – an anadromous fish with a lifecycle similar to salmonids – also returns to coastal streams to spawn and has been observed in the San Lorenzo River (SH&G et al. 2002). In addition, there are many marine fish that use the estuary as nursery grounds. Native coastal estuary and lagoon fish species include Pacific staghorn sculpin (Leptocottus armatus), starry flounder (Platichthys stellatus), and topsmelt (Atherinops affinis) (Conrad et al. 2003, SH&G et al. 2002).

Exotic fish species can also be found in coastal streams due to introduction as gamefish, mosquito control, or accidental release. Non-native large-mouth bass, green sunfish, and mosquitofish can be found in stream systems in San Mateo and Santa Cruz Counties (Conrad et al. 2003, SH&G et al. 2002) and yellow-fin goby have been observed in the San Lorenzo Lagoon (SH&G et al. 2002).

References

Conrad, M.T., S. Chartrand, and J. Owens. 2003. "Gazos Creek Watershed Assessment and Enhancement Plan." Coastal Watershed Council and Balance Hydrologics. Prepared for California Coastal Conservancy and California Department of Fish and Game, 92 (plus appendices) pp. View on-line source.

Stanford University Natural Resources Inventory (SUNRI). 1999. Fishes of Stanford University [Web site]. Planning Office / University Architect, Facilities Operations, and Center for Conservation Biology [cited July 23, 2003]. View on-line source.

Federal Interagency Stream Restoration Working Group (FISWRG). 1998. "Stream Corridor Restoration: Principles, Processes, and Practices." GPO Item No. 0120-A; SuDocs No. A 57.6/2:EN3/PT.653. View on-line document.

Hall, E.R. 1981. The Mammals of North America. Second Edition ed. New York: John Wiley & Sons.

Raedeke, K.J., R.D. Taber, and D.K. Paige. 1988. Ecology of Large Mammals in Riparian Systems of Pacific Northwest Forests. In Streamside Management: Riparian Wildlife and Forestry Interactions, edited by K. J. Raedeke. Seattle, WA: University of Washington, Institute of Forest Resources.

Riparian Habitat Joint Venture (RHJV). 2000. "Version 1.0. The Riparian Bird Conservation Plan: A Strategy for Reversing the Decline of Riparian Associated Birds in California." California Partners in Flight. View on-line document.

Swanson Hydrology and Geomorphology, Native Vegetation Network, and Hagar Environmental Science. 2002. "Lower San Lorenzo River and Lagoon Management Plan." Prepared for City of Santa Cruz Redevelopment Agency, San Lorenzo Urban River Task Force, City of Santa Cruz, State Coastal Conservancy.

Warner, R.E. 1979. "The California Riparian Study Program. Phase I: Background Studies and Program Design for Phase II." California Department of Fish and Game, Planning Branch. 179 pp.

Williams, D.F., and K.S. Kilburn. 1984. Sensitive, Threatened, and Endangered Mammals of Riparian and other Wetland Communities in California. In California Riparian Systems: Ecology, Conservation, and Productive Management, edited by R. E. Warner and K. M. Hendrix. Berkeley, CA: Berkeley: University of California Press. View on-line source.

Back to top