The floodplains of the Sacramento and Feather River support the largest documented population of Bank Swallows (Riparia riparia) west of the Great Lakes region. Bank Swallows depend upon fluvial geomorphic processes to create and maintain their nesting substrate of steep vertical banks and friable soil. These processes also drive the complexity and overall biodiversity of riparian ecosystems. Bank Swallows have declined significantly within the watershed. Conservation efforts call for improved understanding of the distribution and condition of habitat resources, and identification of recovery measures. Here I present a novel analysis that links soil-suitability mapping to a physics-based model of river meander (MeanderJP). I correlated colony locations with key soil characteristics derived from the SSURGO database (USDA-NRCS 2018). I also evaluated the incremental effects of flow impairment and flood control infrastructure on the interactions of river meander and suitable soils. Both soil suitability and river meander extent have extremely limited overlap on the landscape over 50-year modeling scenarios and vary significantly by river reach due to local geology, river planform, levees, and bank stabilization. Dam operation has reduced historical suitable soil-river meander interactions by 24%, and flood control infrastructure has further limited these interactions by 24%, for overall habitat reductions of 48%. Last, I evaluated the return of Bank Swallows at 18 locations where rock revetment no longer remained in place, and in all but 2 instances Bank Swallows colonies were re-established. These findings provide a fundamental understanding of habitat suitability and river process which can be used to prioritize locations where process-based restoration of the Sacramento River and Feather River corridors should occur in order to ensure species persistence and recovery.

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.

Quantitative population objectives are necessary to successfully achieve conservation goals of secure or robust wildlife populations. However, existing methods for setting quantitative population objectives commonly require extensive species-specific population viability data, which are often unavailable or are based on estimates of historical population sizes, which may no longer represent feasible objectives. Conservation practitioners require an alternative, science-based method for setting long-term quantitative population objectives. We reviewed conservation biology literature to develop a general conceptual framework that represents conservation biology principles and identifies key milestones a population would be expected to pass in the process of becoming a recovered or robust population. We then synthesized recent research to propose general hypotheses for the orders of magnitude at which most populations would be expected to reach each milestone. The framework is structured as a hierarchy of four population sizes, ranging from very small populations at increased risk of inbreeding depression and extirpation (< 1,000 adults) to large populations with minimized risk of extirpation (> 50,000 adults), along with additional modifiers describing steeply declining and resilient populations. We also discuss the temporal and geographic scales at which this framework should be applied. To illustrate the application of this framework to conservation planning, we outline our use of the framework to set long-term population objectives for a multi-species regional conservation plan, and discuss additional considerations in applying this framework to other systems. This general framework provides a transparent, science-based method by which conservation practitioners and stakeholders can agree on long-term population objectives of an appropriate magnitude, particularly when the alternative approaches are not feasible. With initial population objectives determined, long-term conservation planning and implementation can get underway, while further refinement of the objectives still remains possible as the population’s response to conservation effort is monitored and new data become available.