San Francisco Estuary and Watershed Science

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.