Abstract
Author(s): Tsao, Danika C.; Melcer, Jr., Ronald E.; Bradbury, Michael | Abstract: Past studies documenting the distribution and status of state “Threatened California black rail (Laterallus jamaicensis coturniculus; hereafter black rail) have largely omitted the Sacramento—San Joaquin Delta (hereafter Delta). During March to May of 2009–2011, we conducted call–playback surveys to assess the status of the species within a wide range of wetland habitats of the central Delta region. We detected black rails at 21 of 107 discrete wetland sites, primarily on in-channel islands with dense cover. To better understand the habitat and land cover characteristics, we developed a model of habitat suitability from these occurrence data and a fine-scale vegetation and land use dataset using MaxEnt. We also evaluated differences in the size of wetlands at sites where black rails were detected versus where they were not. Through surveys and quantitative modeling, we found black rail presence differed from other regions within California and Arizona, in that it was positively associated with tall (1 to 5 m) emergent vegetation interspersed with riparian shrubs. Specific plants correlated with black rail presence included emergent wetland (Bolboschoenus acutus, B. californicus, B. acutus, Typha angustifolia, T. latifolia, Phragmites australis) and riparian (Salix exigua, S. lasiolepis, Rosa californica, Rubus discolor, Cornus sericea) species. Median patch size was significantly larger and perimeter-to-area ratios were significantly lower at wetland sites where black rails were found. These results provide a preliminary characterization of black rail habitat in the Delta region and highlight the need for better understanding of this listed species’ population size and habitat use in the region, in light of anticipated climate change effects and proposed large-scale restoration in the Delta.
Highlights
The California black rail (Laterallus jamaicensis coturniculus; hereafter black rail) resides in a variety of wetland habitats across its range in California and Arizona (Eddleman et al 1994)
The most geographically extensive occupied habitats exist in the San Francisco Estuary, along the Petaluma and Napa rivers, San Pablo Bay, Suisun Bay, and Suisun Marsh, which supports a large proportion of the subspecies (Evens et al 1991; Spautz et al 2005)
Tsao, unreferenced, see “Notes”; CV Birds 2015). We recognize that this model does not capture the potential influence of other important environmental factors such as elevation, more quantitative measures of vegetation structure, or effects of adjacent land use; our results indicate that black rail presence is associated with both tall (> 1 to 5 m) emergent wetland vegetation (Bolboschoenus spp., Typha spp., Phragmites australis) and woody riparian shrub species (Cornus sericea, Salix lasiolepis, and S. exigua)
Summary
The California black rail (Laterallus jamaicensis coturniculus; hereafter black rail) resides in a variety of wetland habitats across its range in California and Arizona (Eddleman et al 1994). Surveys conducted in the 1970s found black rails at Big Break Regional Shoreline (Contra Costa County), and Tule Island and White Slough Wildlife Area (San Joaquin County; Winter and Manolis 1978; Manolis 1977; Manolis 1978; Laymon and Shuford 1979). Two individuals were detected on Bacon Island (San Joaquin County) in a 1986–1988 study that documented a low abundance (0.25 birds per survey station) within the Delta; this study only covered the western extent of the Delta (Evens et al 1991). Black rails were detected in 1992–1993 at several sites within the central Delta during surveys conducted by California Department of Fish and Game
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