PRINCIPAL INVESTIGATOR: Barbara Kus, San Diego Field Station

BACKGROUND AND JUSTIFICATION: Riparian habitat in the southwestern United States has undergone serious declines during the last several decades, prompting efforts to create and restore woodlands throughout their historical distribution. Much, if not most, of this restoration has been driven by the need to compensate for the loss of habitat supporting endangered species such as the least Bell’s vireo (Vireo bellii pusillus) and southwestern willow flycatcher (Empidonax traillii extimus), and restoration has become an important tool during the last decade for regulatory agencies such as the U.S. Fish and Wildlife Service. While habitat creation has been shown to be successful in producing nesting habitat for some endangered species, at least in the short term, little information is available on the long-term viability of restored sites, nor their ability to persist as self-sustaining ecosystems. Moreover, few data exist on the use of restored sites by the broader riparian bird community. Although endangered species provide the legal impetus for habitat restoration and serve as the yardstick by which "success" is measured, restoration can only be deemed truly successful when the restored habitat supports the full range of native species present in natural habitat.

The purpose of this investigation is to evaluate the use of restored habitat by riparian birds and thereby provide data on the effectiveness of restoration as a means for replacing lost natural habitat and its associated animal communities. Specifically, we will quantify the development of planted vegetation over time, and compare bird species richness, abundance, and productivity in the restored site with that in an adjacent natural "reference" site. We predict that as vegetation structure in the restored habitat approaches that of the reference site, the two bird communities will increase in similarity. This project extends and expands previous work focusing on least Bell’s vireo use of restored habitat, and will provide resource agencies and wildlife managers with information on the value of restoration to wildlife beyond endangered species.

OBJECTIVES: The objectives of this study are to (1) describe quantitatively the structural development of planted vegetation in the riparian restoration site, and compare it to the structure of natural reference habitat and (2) quantitatively compare bird use of the restoration site to that of natural reference habitat with regard to species composition, abundance, and productivity. We project a study period of at least five years (1997-2001).

STUDY AREA: The study site is located along Pilgrim Creek, a tributary to the San Luis Rey River in northern San Diego County, California. The site supports natural stands of riparian and coastal sage scrub habitat, as well as planted vegetation intended to restore former expanses of these two habitat types in areas converted by agriculture. Protection of the existing habitats through acquisition, and the restoration of natural communities at the site were undertaken as mitigation for impacts to riparian and coastal sage scrub habitat produced by a nearby highway expansion project. The stretch of Pilgrim Creek on the site supports approximately 4 ha of willow-dominated riparian habitat along a narrow channel. Coastal sage scrub, including 14 ha of restored habitat, covers the slopes bordering the site to the west, and the center of the site supports riparian vegetation planted in 1996 within an 11-ha restoration area, as well as a 0.6-ha freshwater marsh. An additional small cell of planted riparian vegetation lies between Pilgrim Creek and Douglas Drive on the east side of the river.