Developing a Riparian Bird Index to Communicate Restoration Success in Marin County, California

Despite being widely recognized as an important component of successful restoration, ecological monitoring to evaluate project success is often not conducted (Bernhardt et al. 2005). Even when projects are monitored, data may not be used to its greatest capacity, usually because monitoring has been conducted without specific measures of success (Ruiz-Jaen and Aide 2005). As a result, the ability to provide stakeholders with relevant and timely information about restoration progress is limited. There is a need to develop monitoring frameworks that clearly define restoration success and provide pathways to improve restoration performance and ultimately to enhance ecosystem performance from investments in restoration. To address these challenges in the context of riparian restoration in coastal California, we used historical monitoring data from reference and restoration sites in Marin County to develop a Riparian Bird Index (RBI). This index is essentially a species richness score for a given area that is weighted by the degree to which each species detected is associated with target riparian vegetation and can be converted into a simple “poor,” “fair,” “good,” or “excellent” rating to communicate restoration success to a diverse audience.

To develop this method, we used bird occurrence data obtained from the area search method from reference and restoration sites, which is an effective, simple, and efficient means of collecting information about the diversity and abundance of birds, especially for small-scale projects (Ralph et al. 2003). The area search method involves defining an area, spending 20 min searching it, and recording all birds that are encountered. While quantitative, this method is similar to the process a recreational birder would use to search for birds and is therefore especially useful for engaging citizen scientists in monitoring. Methods for conducting area searches are available on-line: data.prbo.org/cadc2/index.php?page=songbird-area-searches.

Between 2004 and 2010, we conducted area searches at 4 riparian reference sites in Marin County: Pine Gulch, Muddy Hollow, Redwood Creek, and Lagunitas Creek. These sites are large areas of mature riparian vegetation, comprised of willows (Salix spp.), red alder (Alnus rubra), and a diverse understory. Area search plots at these sites ranged from 1.3 to 4.3 ha. At 2 plots on each site, we conducted surveys multiple times each month throughout the fall (mid-August through October) as part of an unrelated study. Here, we have restricted our analysis to area searches conducted in the month of August, with the expectation that the birds recorded during this time (late summer/early fall) are most reflective of birds that are present during the breeding season (April to early August). During August, we surveyed each area search plot 12–16 times using a standardized method (e.g., during morning hours and on a rotating schedule) to minimize the potential for any temporal bias across the plots.

Between 2001 and 2009, we conducted area searches at multiple restoration sites on private lands in Marin County. To illustrate the utility of the RBI, we focus on 3 of these sites here. These sites were small creeks that would have been lined by willows and alders, yet as a result of land-use practices, were denuded of trees and shrubs; only grasses were present. Restoration at these sites involved fencing to remove livestock and replanting of riparian vegetation. Within 3–5 yr after restoration, the sites had substantial increases in vegetative cover, especially of willows. Area search plots at these sites ranged from 0.31 to 1.15 ha. At each site there were 3 area search plots, and we surveyed these plots twice each year during the breeding season (April to August).

Using expert opinion, published literature on avian habitat associations, and a list of bird species that were detected over 7 yr of monitoring at the 4 reference sites, we developed 3 tiers of bird species groupings that serve as restoration targets. The first tier was comprised of 10 bird species that are strongly associated with riparian vegetation or other riparian characteristics. The second tier was comprised of 16 species that, although not strongly associated with riparian...