Eastern Sierra Riparian Songbird Conservation Project
Using songbirds as a tool to assess the health of Mono Basin riparian systems
By Sacha Heath
Riparian habitats in the Mono Basin are diverse, both in vegetative structure and plant species composition. These habitats include canopied forests of aspen, lodgepole pine, and black cottonwood with an understory of snow berry and mugwort; newly established stands of scrub willow, wild rose and cottonwood saplings; and remnant groves of cottonwood gallery mixed with decayed snags. Mono Basin creeks are a small but important component of Californias remaining riparian habitat515% of its original size. These habitats are criticalnot only for the plants, insects, humans, and the health of Mono Lake itself, but also for the songbird species that depend on them for breeding, migration, and over-wintering.
Riparian habitat has long been identified as one of Californias most critical habitats for neotropical migrant and resident songbirds. Joseph Grinnell and Alden Miller documented this in the 1920s by mapping the distribution of California songbirds. David Gaines continued their work in the 1970s and alerted the conservation community to the disappearance of many riparian breeding songbirds in the Central Valley.
Recently, continent-wide collaborations have been formed among government agencies, non-profit organizations, and private groups to address the issue of habitat loss and the subsequent decline of songbirds. One such effort, California Partners in Flight, identified habitat loss as the major cause of songbird declines, and riparian habitat as the most endangered among these. As a result, the Riparian Habitat Joint Venture was established with the mission to promote conservation and restoration of riparian habitat sufficient to support the long-term viability and recovery of native bird populations and associated species.
The relationship between songbirds and riparian habitat is reciprocal, and birds provide an excellent means to track larger changes in riparian systems. Birds occupy a diverse range of niches and are sensitive indicators of ecosystem health. Managing for songbird diversity can protect many other elements of biodiversity, including the processes that are inherent in riparian systems. These physical and biological processes include hydrology, geomorphology, insect and fish production, and plant succession. Songbird monitoring on Mono Basin creeks provides us with such a measure of ecosystem health.
The Eastern Sierra Riparian Songbird Conservation Project was initiated as a collaborative effort spearheaded by the Point Reyes Bird Observatory (PRBO), Bureau of Land Management Bishop Resource Area (BLM), and the Inyo National Forest (USFS) in the spring of 1998. The project seeks to investigate songbird use of riparian habitats in the Eastern Sierra by utilizing nationally standardized songbird monitoring methods. Other project supporters include the National Fish and Wildlife Foundation, Region 5 Partners in Flight, California Department of Fish and Game (CDFG), Mono Lake Committee (MLC), Eastern Sierra Audubon Society (ESAS), Eastern Sierra Institute for Collaborative Education, Mono Lake Tufa State Reserve, Los Angeles Department of Water and Power, Southern California Edison, and Conway Ranch/Trust for Public Land.
Overall, the project documents songbird use of twenty nine creeks and two sections of the Owens River along a 232 km stretch of the Eastern Sierra, ranging from Olancha north to Bridgeport. Within the Mono Basin, we are investigating six areas: Lee Vining, Rush, Mill, Wilson, and Dechambeau creeks and Indian Springs. The project design replicates those used on all of PRBOs riparian study sites and results can be compared on a local, regional, and statewide scale. For the past two years, we have monitored these sites with extensive point counts, area search surveys, and vegetation analysis. These methods provide information on songbird breeding distribution, bird abundance, bird species richness (number of species), and bird diversity on these creeks.
Our data is helping to refine the most current understanding of riparian songbird distribution in California. We are comparing current breeding distributions with historic range maps drawn by Grinnell and Miller in order to demonstrate areas of species extirpation or range expansion. We focus on a host of 14 riparian focal species whose breeding requirements represent the full range of successional stages of riparian ecosystems.
So far, we have found that Mono Basin creeks provide breeding habitat for four of these focal species and migration stop-over habitat for three others. Yellow Warblers, Song Sparrows, and Warbling Vireos were found in abundance on both the more-established higher reaches and the regenerating lower reaches of Mono Lakes tributaries. Once common throughout the state, these species have recently experienced declines and/or extirpations in other riparian habitats in California. Figure 1 displays the historic and current breeding distribution for the Yellow Warbler in California. Two historic breeding speciesSwainsons Thrush and Willow Flycatcher no longer breed in the Mono Basin, but have been detected as migrants.
Mono Basin creeks had generally higher indices of songbird diversity and species richness in the upper versus lower reaches. Additionally, Mono Basin sites had higher indices than those found for the Owens Valley alluvial fan sites. Differences in riparian type (ie aspen vs. desert riparian types) probably accounts for much of this variation, so the two should be compared with caution. Additional analysis of bird data and accompanying vegetation and landscape variables may provide insight into what features birds in the Mono Basin key into. Managers may apply these results to improve restoration efforts in other regions of California where some of these species have disappeared.
Species diversity and abundance are good general indices of bird population trends, and breeding status provides insight into distributional changes. However, the evaluation of population health requires a thorough investigation of demographic processes that drive songbird populationsnamely reproductive success (number of young produced in a year), survival (year-to-year or over-winter survival), and dispersal and recruitment (the movement of new breeders into or away from a population). Starting this spring, the project will expand to more intensively investigate reproductive success and survival of songbirds utilizing Mono Basin creeks.
Recent studies indicate that songbird declines in North America are largely due to breeding ground limitations. For riparian-dependant songbirds, loss of habitat is the primary limitation in California. Where habitat exists, and birds continue to attempt breeding, predation by both native and domesticated species is the primary cause of nest failure in many open-cup nesting songbirds. The expansion of the Brown-headed Cowbird (a species which lays its eggs in the nests of other, smaller songbird species) in the West also contributes to low productivity in songbirds. Other limiting factors include land uses that compromise the integrity of riparian systems such as over-grazing, human development, and the suppression of natural processes (flooding, fire etc.). Poorly timed management practices such as vegetation clearing or burning during the breeding season also impairs reproductive success. Finally, restoration efforts that do not take into account habitat requirements of breeding songbirds may create ecological traps. Birds may suffer poor nest success if they are attracted to a system that lacks proper microhabitat components (nest concealment and insect production) or that supports inflated predator or nest parasite populations.
The Mono Basin still harbors an abundant riparian songbird community, including species that have been extirpated in other regions of California. Additionally, with the re-watering and subsequent recovery of the Basins creeks, new habitats will become available for songbird use. We now have the opportunity to assess current habitat conditions and to track the recovery of songbirds and their habitat over time. These results may illuminate poorly understood habitat requirements for key riparian species and can potentially be extrapolated to regions of California where these species are missing. We will apply this information in the form of recommendations to land managers, locally and statewide.
You may access information about this project and statewide riparian songbird conservation projects at PRBOs website: www.prbo.org. Copies of Eastern Sierra Riparian Songbird Conservation reports are available at the MLC and ESAS, the Bishop offices of BLM, USFS, and CDFG, and PRBO.
Sacha Heath works for the Point Reyes Bird Observatory and is co-principal investigator for the Eastern Sierra Riparian Songbird Conservation Project
The Committee was awarded a $25,000 grant from the Commission for Environmental Cooperation (CEC) to integrate migratory bird stuides with restoration activities in the Mono Basin. The CEC is a Montreal-based organization created by Canada, the U.S., and Mexico to address environmental issues in North America from a continental perspective. CEC funds will be used for riparian songbird monitoring discussed here, gull research in the Mono Basin, and a web-based clearinghouse to share the information with the public. Click here to read the reports online.