Quarterly Journal of PRBO Conservation Science. Number 128, Spring 2002. $2.50

Vulnerable songbirds breeding in remnant tidal marsh habitat are the focus of multifaceted PRBO research —and of this special Observer issue.

▼ Insights into the health of a threatened ecosystem Tidal Marsh Song Sparrows of San Francisco Bay

Introduction

Nadav Nur, PhD an Francisco Bay is the largest Much of it consists of small remnant estuary on the Pacific coast of the habitat patches in a sea of diked or SUnited States. Its wetlands pro- developed baylands. It is often abutted vide crucial habitat for a wide range of by freeways and shopping centers and Alameda Song Sparrow species. Millions of shorebirds and sometimes criss-crossed by manmade waterfowl use the estuary and adja- ditches and power lines. scientific foundation for the design and cent baylands, either as wintering A number of distinctive organisms evaluation of restoration projects. grounds or as “refueling” areas during have evolved to take advantage of this The Tidal Marsh Bird Project is fall and spring migrations up and productive habitat and are restricted to one component of a larger effort by down the Pacific Flyway. In addition, it. In San Francisco Bay, these include prbo—our San Francisco Bay Habitat many bird species and other wildlife birds—California Clapper Rail, Project—to study, maintain, and sus- inhabit San Francisco Bay wetlands California Black Rail, Alameda Song tain the broad array of bird species that year-round. A lack of alternative habi- Sparrow, San Pablo Song Sparrow, depend on the entire mosaic of habitats tats makes them vulnerable, especially Suisun Song Sparrow, and Saltmarsh in the Bay. Our focus ranges from the species that depend upon tidal Yellowthroat; plants, such as Suisun shorebirds feeding on invertebrates in marshes fringing the estuary. thistle and soft bird’s-beak; and other tidal mudflats to cormorants foraging Salt-water marshes—subject to wildlife, such as the salt-marsh harvest in the open waters of the Bay. tidal action, marked by extensive net- mouse and San Francisco garter snake. While our tidal marsh work works of sloughs and channels, and The effect of extensive habitat loss includes all the birds that rely upon characterized by salt-tolerant plants and degradation has been to put these this habitat, we have focused much such as pickleweed and gumplant— populations at risk. As a consequence, attention on three unique subspecies represent a vital ecosystem. Among management agencies and the scientific of nesting Song Sparrows. Studying their ecological functions, marshes community have placed a premium on these birds can be fruitful in advanc- enhance the Bay’s water quality by fil- developing programs to conserve ing the nascent science of restoration. tering toxic compounds out of the remaining populations and restore The threats they face—habitat frag- runoff from surrounding uplands. depleted species, through maintaining mentation, changes in salinity, expo- In the early nineteenth century, tidal and restoring tidal marsh habitat. sure to pollutants, non-native invasive marsh was the dominant habitat type in Against this backdrop, prbo’s species, and more—are ones faced by San Francisco Bay. Its historic acreage Tidal Marsh Bird Project began in the whole community of tidal marsh has been reduced by about 85%, due to 1996. Its aims are: to provide manage- fauna. In this Observer issue, we sum- development as well as diking for agri- ment agencies with critical information marize some of our recent findings. culture and salt evaporation ponds. about the status of tidal marsh-depend- Even what remains of this habitat today ent species; to guide recovery efforts for Nadav Nur, PhD, is Director of PRBO’s has been severely altered and degraded. these populations; and to establish a Population Ecology Program.

Peter LaTourette Page 2 PRBO Conservation Science, Spring 2002 While all three subspecies face significant threats, the one requiring the most urgent attention is the Alameda Song Sparrow.

Significant Findings

Nadav Nur, PhD, and Hildie Spautz Song Sparrows do not appear to o provide management agen- respond to vegeta- cies with information about the tion height and Tstatus of tidal marsh-dependent density of plant species, and how best to protect and stems (unlike the San Francisco facilitate recovery of their populations, Marsh Wren and prbo conducts standardized surveys of Salt Marsh Yellow- Song Sparrows each year at over 50 throat). They do marshes throughout the San Francisco respond positively Bay Estuary. Some results to date: to shrub cover, Virtually every Bay tidal marsh has mostly gumplant one or more pairs of Song and coyote brush, Sparrows (Yellowthroats and Black and negatively to Rails are found in some marshes Juncus (rushes). Figure 1. Distribution of three subspecies of tidal marsh Song but not others). There are strong Sparrows on San Francisco Bay. There is marked variation in Song associations Sparrow population density among between Song Sparrow density and about 12,000–18,000; Suisun Song marshes, even within a sub-region landscape features. In particular, Sparrows, 40,000–66,000; San Pablo such as San Pablo Bay. density is greater in marshes that Song Sparrows, 70,000–85,000. These In San Francisco Bay marshes, are larger, not isolated from other numbers are greater than previously inhabited by the Alameda Song marshes, and not adjacent to urban estimated for San Pablo and Suisun Sparrow, we estimate an average areas. This information is of great Song Sparrows but similar to previous density of 5.2 birds per hectare value—both to inform current estimates for the Alameda Song (100 meters2). San Pablo and habitat management practice and Sparrow. While all three subspecies Suisun Bay marshes, inhabited by for prioritizing new acquisition and face significant threats, the subspecies the other two subspecies, demon- restoration programs. requiring the most urgent attention of strate average densities of 14.9 Our estimates of density allow us management agencies is the Alameda birds per hectare. to estimate the total breeding popula- Song Sparrow, which is also the most Habitat characteristics may explain tion size for each of the three sub- genetically distinctive subspecies of spatial variation in abundance. species: Alameda Song Sparrows, the group.

Tidal Marsh Fragmentation: Edge Effects Having found nest predation to be a main cause of Song Sparrows’ nest failure, we investi- Bay edge gated the effects of marsh edge proximity on predation rate and overall nest success. For five San Pablo and Suisun Bay marshes, we looked at the fate of more than 1,800 Song Sparrow nests monitored between 1996 and 2000. Nests located closer to the Bay edge fledged young sig- nificantly more often than did nests located closer to upland marshland edges. Our analyses, however, suggest that the edge characteristics of an entire marsh may be more important than the location of nests within a marsh. Landscape-level conservation planning is needed in upland edge order to identify conservation/restoration sites most hospitable to Song Sparrows and other marsh-dependent species.—Diana Stralberg, meters Geographic Information Systems Specialist, and Yvonne Chan, Seasonal Biologist

Figure 2. Song Sparrow nests at China Camp State Park (San Pablo Bay) in 1997. Black dots are nests that successfully fledged young. Red stars are nests that were depredated. Black triangles are nests that failed for other reasons.

prbo graphics PRBO Conservation Science, Spring 2002 Page 3 A growing concern for all wildlife reliant on San Francisco Bay is the accumulation of chemical pollutants in the water, sediments, and food web.

Contaminants and Nest Success

Right:A PRBO field Hildie Spautz biologist examines an he San Francisco Bay ecosys- inactive marsh nest site. tem is much altered from the one eggs that he collected where tidal marsh Song T from nests on the Sparrows evolved, several thousand Richmond–San Rafael years ago. A growing concern for all Bridge. Eggs from wildlife reliant on San Francisco Bay is 1999 and 2000 have the accumulation of chemical pollu- been tested for nine tants in the water, sediments, and food chemical contaminants. cern in avian eggs, and eggs that failed web. Sources of toxic compounds, Cormorants’ eggs had much higher to hatch had selenium levels similar to especially in the northerly arm, San levels than sparrows’ for eight of the those of viable eggs, indicating that egg Pablo Bay, include runoff from agricul- nine compounds (e.g., dde, pcbs, and mortality is probably not directly relat- ture and discharges from industries mercury), likely reflecting differences ed to higher levels of environmental fringing the Bay. between their ecological niches. selenium in parental diets. P ’s study of Song Sparrows’ rbo Sparrows are restricted to tidal marsh- In field observation of nests reproductive success in San Pablo and es and consume plant material and throughout their cycle, we document Suisun Bays has found reproductive invertebrates; cormorants, higher on the proportion of eggs that hatch. We rates to be disturbingly low. Predation the food-chain, forage for fish in the have found no statistically significant is a main cause of nest failure. differences between tidal marsh The probability that a nest sur- nests and those at prbo’s vives to fledge at least one young Palomarin Field Station (belong- averages less than 20% per year; ing to the Marin Song Sparrow for some marshes, the rate is subspecies), or between San 10% or less. Nest survival must Pablo and Suisun Bay eggs. No approach 25% to yield long-term detectable pattern of reduced sustainability of the populations. hatchability in Bay marshes at As shown in Figure 3, there is this time is good news! great variability among years and San Pablo Song Sparrows and among marshes, and San have higher rates of overall nest Pablo Song Sparrows display success (young that fledge) than higher reproductive success than Suisun Song Sparrows, due pri- their Suisun neighbors. marily to differences in predation Attention now is focused on Figure 3. Song Sparrow nest survivorship in San Pablo Bay (solid lines) and Suisun Bay (dotted lines), 1996-2001. rates. Notably, Marin Song factors that may contribute to low Sparrows at Palomarin show nest success. Environmental con- Bay and may bioaccumulate more higher nest success than either tamination can cause reductions in environmental contaminants. San Pablo or Suisun birds. maternal fertility, increases in embryo One chemical that rang a potential We aim next to add Suisun and and nestling abnormalities, and thin warning bell for sparrows was seleni- Palomarin birds to our contaminant shells. In 1999, prbo joined a new, col- um. Concentrations in sparrow eggs study, and to evaluate whether regional laborative study aimed at designing a were 30% higher than in cormorants, differences in nest success may be due monitoring network sensitive enough to ranging from 2.2 to 4.5 parts per mil- to broadscale differences in exposure to provide advance warning, at a cost-effi- lion (ppm) dry weight. However, this is contaminants. cient scale, of the ecological impacts of below the 6.0-ppm threshold for con- contaminants in San Pablo Bay.1 We Hildie Spautz is Supervisory Biologist in the have collected Song Sparrow eggs at 1 Our project, with physical and biological scientists from Tidal Marsh Project of PRBO’s Population Ecology three San Pablo Bay marshes. Dr. Jay U.C. Davis and the San Francisco Estuary Institute, is for- Program. mally called the San Pablo Bay Network of Environmental Davis of San Francisco Estuary Institute Stress Indicators. Funded by the Environmenatl Protection This work was made possible by grants from performs chemical analyses on these Agency, it is part of the National Oceanographic and Atmospheric Administration’s Coastal Intensive Sites the U.S. Environmental Protection Agency, and also on Double-crested Cormorant Network (cisnet). The full text of our most recent cisnet the Richard Grand Foundation, and the report can be found on prbo’s website at www.prbo.org/tm. Bernard Osher Foundation.

prbo graphics Page 4 PRBO Conservation Science, Spring 2002 Ultimately, our results can help shape conservation priorities and restoration efforts.

Suisun Bay. On San Pablo Bay lives the the other tidal marsh subspecies and Genetic Distinctions Samuel’s Song Sparrow, smaller in size from the closest upland subspecies. Yvonne Chen and blackish-olive on the back. The Samuel’s and Suisun Song Sparrows, Alameda Song Sparrow in South San however, are genetically indistinguish- radling the Song Sparrow Francisco Bay, slightly smaller yet, has able—and are genetically similar to a gently in my hand, I worked a yellowish-grey back color and is the population of the Modesto Song Cquickly to record the measure- only subspecies with a yellowish wash Sparrow (a fifth subspecies) on the ments: back color, bill width, length of to the belly. In the coastal sage scrub Cosumnes River! wing, tail, and leg. I obtained a small along the coast and lining fresh-water The Alameda Song Sparrow is drop of the bird’s blood, then released riparian corridors is the reddish-brown genetically the most unique of the it to flutter off, none the worse for the Marin Song Sparrow, intermediate in three. It is also the subspecies most experience. size between the Suisun and the other threatened by habitat destruction, with It was one of the remarkable four two marsh subspecies. less than 10% of its original habitat subspecies of Song Sparrow that reside Are these different-looking sub- remaining. This highlights the need to year-round in the Bay Area. Three of species genetically distinct? Investigat- prioritize conservation efforts in South these are endemic to tidal salt marshes ing this, I examined genetic markers in San Francisco Bay and provides sup- fringing San Francisco Bay (Figure 2); small blood samples from over 200 port for applying for Endangered the fourth inhabits nearby uplands. Song Sparrows from nine populations Species Status for the Alameda Song The tidal marsh subspecies are current- around the Bay. The upland subspecies, Sparrow. Ultimately, our results can ly listed as Species of Special Concern the Marin Song Sparrow, is genetically help shape conservation priorities and in California because of dramatic distinct from the tidal marsh popula- restoration efforts. reduction in their habitat and questions tions, even though it nests in an adja- about their long-term viability. cent (but different) habitat. Yvonne Chan, a PRBO Seasonal Biologist, was a The bird I handled, chocolate Among the three tidal marsh sub- 1997-98 Field Supervisor in the Tidal Marsh brown, was a Suisun Song Sparrow, Project.The research reported here is part of her species, the Alameda Song Sparrow is Masters thesis from the University of British found only in the brackish marshes of the most divergent form, differing from Columbia.

CALENDAR OF PRBO EVENTS

PRBO BIRD WALKS Morning outings in or near Point Reyes BIRDING WITH RICH STALLCUP Seasonal day trips, advance National Seashore, $5 donation, free to PRBO members. registration required, $25. Sunday, June 9 ■ Tidal Marsh. Visit one of prbo’s study sites on August 25 ■ Abbotts Lagoon. A great destination for shore- northern San Francisco Bay. birds, waterfowl, and nearshore ocean bird sightings. Saturday, July 6 ■ Birds of Redwood Creek. In riparian habi- September 22 ■ Bodega Bay. Exploring a variety of habitats tat near Muir Beach, learn about prbo nest monitoring. filled with autumn birds. Sunday, August 4 ■ Coastal Scrub & Riparian Canyons. At October 12 ■ The Outer Point of Point Reyes. A search for Palomarin Field Station, we look for (and band) fledgling birds. fall migrants (and vagrants!) and seabirds. Sunday, September 1 ■ Snowy Plovers. An inside look at prbo For more information about PRBO Bird Walks or Birding with efforts to protect and restore a threatened species. Rich Stallcup, call Melissa Pitkin at 415/868-1221, extension 307. OF SPECIAL INTEREST Please mark your calendar! October 10 ■ 2002 Osher Symposium. Highlighting the achievements of prbo’s outstanding intern biologists. September 21–October 5 ■ Bird-A-Thon 2002. Any 24-hour period between these dates. Watch for details in the mail! December 7 ■ Bird-A-Thon Awards Dinner. Annual classic; everyone welcome.

PRBO—working to conserve birds, other wildlife & their ecosystems through innovative scientific research & outreach.

PRBO Conservation Science (founded in 1965 as Point Reyes Bird Observatory) is a non- C Printed on recycled paper using soy-based inks profit 501(c)3 organization with headquarters at Stinson Beach, California. All memberships and contributions are tax-deductible to the extent allowed by law. Annual memberships are: The PRBO Observer is published quarterly by the PRBO Board of Directors. Edited Benefactor: $1,000 & more Sustaining: $250 Family: $50 Student & and designed by Claire Peaslee, assisted by members of PRBO ’s staff. Copyright © Sponsor: $500 Contributing: $100 Regular: $35 Senior: $20 2002 PRBO Conservation Science.

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