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54 STATE OF THE ESTUARY TIDAL MARSH BIRDS CONTEXT Buzzy calls and trills ringing out from the marshes around the Estuary are often the first clue to finding the sometimes-secretive songbirds and rails that live there. Tidal marsh birds are valuable indicators of tidal marsh ecosystem condition. San Francisco Estuary tidal marsh habitat has been dramatically altered in the past two centuries. Over 80 percent of the original tidal marsh habitat in the Bay region has been lost. Many of the species that depend on tidal marsh habitat are cur- rently listed as federally- or state-threatened or endangered, such T I D A L M A R S H B I R D S as the California B AY black rail, or are designated as . . S TAT U S . . California Species Fair of Special Con- . . . .T R E N D . . . . cern (tidal marsh Increasing song sparrow .....BENCHMARK..... species and the Upper quartile population saltmarsh com- density, 1996-2008 mon yellowthroat). INDICATOR 1.4 1.0 Fair 1.2 BAY Good 1.6 INDEX 0.8 0.4 Poor 0.6 0.2 2015 2013 2011 2009 2007 2005 2003 2001 1999 1997 1995 0 This indicator is an index that measures the current condition of three tidal marsh-dependent bird species, providing insight into success at recovering or maintaining these threat- ened populations. The indicator measures the breeding season abundance of the California black rail (Laterallus jamaicensis coturniculus), song sparrow (Melodia melospiza subspecies), and common yellowthroat (Geothlypis trichas sinuosa). Subspecies of all three live and breed in the Estuary. They are uniquely adapted to tidal marsh habitat and are of conservation concern. Standardized surveys of these species have been conducted in tidal marsh habitat since 1996, and from this an index of population density was constructed, combining results for the three species. Data from the most recent four years of surveys (2011-2014) for all three species combined was compared to benchmark values. Ten marshes were surveyed regularly during 1996-2014, from about ten stations per marsh. Birds were identified and enumerated within 50 meters of an observer. STATUS & TRENDS The three species Tidal Marsh Bird Population Index varied from 0.93 birds per hectare to 1.32 birds per hectare during the four years 2011 to 2014, with a mean value of 1.09. The Tidal Marsh Bird Index demon- strated a significant, increasing trend over the entire time period. An average annual growth rate of 2.77 percent over the course of 18 years translates into a total increase of 63 percent. Black rails and common yellowthroats increased significantly over the entire period. Song spar- 2015 rows exhibited a weak, insignificant increase. The overall trend reflects an early increase (1996-2005), followed by no overall increase during the latter period (2005-2014). The best estimate of the trend in the first nine years is 5.1 percent increase per year. In the last nine years, the trend is indistinguishable from 0 percent change. The trend during the entire period of study, 1996 to 2014, is significantly positive. The 2015 Tidal Marsh Bird Population Indica- tor reflects a mixed picture. While there is a general increase in density of the three-spe- cies-index since 1996, no clear increase is evident in the more recent years (2005 to 2014). Furthermore, only two out of the three species demonstrate an increase in density over the entire period, 1996 to 2014. That said, there is no evidence of a decline in density during the entire time period. THREATS & CHALLENGES Reduced, degraded and fragmented habitat, plus the spread of invasive species, have all contributed to reductions in the population size and viability of the birds that depend on tidal marsh. Man- agement and restoration efforts by agencies and NGOs have been directed at recovering deplet- ed populations or ensuring their stability. At this time, habitat is sufficient to maintain populations at their current density and possibly to support an increase in density, at least for rail species and the common yellowthroat. Density is ex- pected to increase as young, restored marshes mature and better support growing populations of tidal marsh bird species. Photo: Rick Lewis