Purpose and Scope

Laterallus jamaicensis jamaicensis (eastern black rail), a subspecies of Laterallus jamaicensis (black rail), were listed as threatened under the Endangered Species Act in 2020. Habitat loss, sea level rise (SLR) and tidal flooding, and storm intensity and frequency were identified as some of the primary threats to the eastern black rail and reasons for the listing decision (U.S. Fish and Wildlife Service, 2020). In subsequent years, extensive research including new distribution modeling has been completed to characterize the environmental needs of these birds now and into the future (Watts and Beisler, 2021); however, the secretiveness of eastern black rails has made assessing some of the current and future threats that are likely to affect this subspecies difficult.

The eastern black rail’s preferred nesting habitat is emergent wetlands, where dense vegetation provides protection from predators. In coastal wetlands, nesting occurs in the high marsh where the soil is wet or the water is shallow. This area may be inundated during lunar and wind-driven tidal events but is at a higher elevation than the area that is inundated by daily tides (Watts, 2016; Stevens and others, 2022). Individual studies have identified nest flooding as a substantial source of mortality for eastern black rails (Hand and others, 2021). Future nest flooding risk is projected to increase because of the combined effects of SLR, high tides, and storm events; however, little information is available on the exact location and success of nest sites with respect to elevation across the entire coastal distribution. Without data on nesting outcomes after flooding events to parameterize a model, quantifying current and future flooding effects on nests at a finely resolved spatial scale is not feasible. Additionally, the scale at which nest flooding occurs in a heterogeneous landscape (for example, habitat and elevation) and the coarse estimates of SLR and tidal height make it difficult to quantify exact flooding risk at a nesting-relevant scale. It is still possible to highlight areas that may face climate stressors compounded with existing habitat challenges.

To assess potential changes to coastal nesting habitat, we used ecological studies for the eastern black rail (Hand and others, 2021; Watts and Beisler, 2021; Stevens and others, 2022) and Ammospiza caudacuta (saltmarsh sparrow; Gmelin, 1788), a species with similar habitat requirements (Bayard and Elphick, 2011; Field and others, 2017); research on marsh resiliency and marsh migration; and projections for SLR. Our goal in this report is to provide a qualitative analysis of potential risks because of environmental changes (relative SLR and high tide flood frequency) in the absence of the necessary data (exact nesting locations, information on renesting frequency and success, and local marsh migration projections) for inclusion in a quantitative model.

The eastern black rail is a cryptic marsh bird that, in the United States, primarily inhabits the Atlantic and U.S. Gulf coasts (fig. 1) with some inland populations in the Great Plains (not shown; Watts, 2016). Coastal parishes and counties that have ocean-connected land less than or equal to 10 feet (ft) (referenced to North American Vertical Datum of 1988) above sea level are denoted on figure 1. For the purposes of this report, which explores changes in tidal flooding caused by climate change, we focus on the coastal distribution of the subspecies, particularly in areas with recent breeding activity (Watts, 2016); six county clusters where gages have relative SLR projections were chosen from these areas to demonstrate a variety of vulnerability (fig. 1).

Eastern Black Rail Ecology

The eastern black rail’s secretive nature has made this subspecies difficult to study (Roach and Barrett, 2015). The studies that provide background for this report primarily used vocalizations to identify rail occurrence. These data do not provide information on breeding ecology including population responses to environmental factors like nest flooding (Watts and Beisler, 2021). Recent advances in camera trap data provide more insight into eastern black rail habitat use but have only been deployed in limited parts of the subspecies’ range (Hand and others, 2021).

The wide but patchy geographic distribution (Stevens and Conway, 2021) of the eastern black rail makes it difficult to comprehensively evaluate subspecies status with relation to their current and future environment; however, surveys and range-wide studies have broadly identified the conditions necessary for eastern black rails (see Watts and Beisler [2021] for recent advances). The eastern black rail is a wetland-dependent bird, and occupancy models indicate that this subspecies prefers high marsh, occupying the transition zone at the edge of nonforested wetlands where dense vegetation provides protection from predators (Stevens and others, 2022) and where elevation provides protection from tidal inundation except during extreme tides (Watts, 2016). Eastern black rails nest and use areas with shallow water or wet soils that stay wet even during dry periods (Hines and others, 2024) and locations where they can build nests high enough to prevent flooding, avoiding low tidal marshes (Watts, 2016; Haverland and others, 2021). Several studies on eastern black rail locations note the importance of this high marsh (Haverland and others, 2021; Stevens and others, 2022).

Flooding Risk to Eastern Black Rail

Because of their reliance on coastal marsh habitat, eastern black rails are at risk from tidal flooding. Eastern black rails are most vulnerable to flooding during nest incubation, brooding, and molting periods. Across their distribution, egg laying and incubation occur between March and August; nesting peaks around the third week of June with no significant difference in timing by region (Watts, 2021). Although documentation on nest outcomes is limited, where it has been studied, nest flooding was the greatest cause of egg loss for the eastern black rail (Legare and Eddleman, 2001). The combined effects of rising sea levels with high tides, particularly during nesting season, have been identified as some of the greatest threats to the subspecies’ productivity and survival (Hand and others, 2021; Watts and others, 2021).

The risk and response of the eastern black rail to nest flooding and increasing flood potential have not been extensively studied. Another coastal wetland bird species with overlapping distribution that also nests in the high marsh, the saltmarsh sparrow, has received more attention. Nest flooding is a major source of nest failure for the saltmarsh sparrow; inundation depth and frequency of nest flooding are strongly correlated with nest failure (Bayard and Elphick, 2011). Population models that incorporate SLR indicate a reduction in successful reproduction to the point of extinction in the absence of marsh migration (Field and others, 2017). For Maryland, Audubon Maryland-DC developed a tool to identify areas for marsh conservation and restoration in the face of SLR specifically targeting the high marsh system used by saltmarsh sparrows (Lerner and others, 2013). The future changes to breeding habitat identified for the saltmarsh sparrow are likely mirrored in future risks to the eastern black rail.

Analysis Range and Habitat Selection

To investigate the future risk of flooding in eastern black rail breeding areas, we determine a range of parishes and counties along the Atlantic and U.S. Gulf coasts for analysis and further restrict analyses to certain land cover types and seasons. Analysis was limited to April–September (a total of 183 days). This period includes likely timing of egg laying, incubation, hatching, and then adult molting when eastern black rails are at risk from inundation (Hand and others, 2021).

Potential habitat is delineated two ways: (1) a conservative approach considers all areas in a county in the 30-meter (m) resolution National Land Cover Database (NLCD) dataset designated as emergent herbaceous wetland (NLCD class 95) to be potential habitat (Dewitz, 2023) and (2) a second designation considers only the transition zone, which is the part of emergent herbaceous wetland within 500 m of woody wetland (NLCD class 90) as potential habitat. The second approach has a reduced absolute area, but inundation percentages tend to be lower because this transition zone is more inland. We compared the NLCD emergent wetland data layer with wetland layers in other products including the 30-m resolution Coastal Change Analysis Program (C-CAP) 2016 Regional Land Cover dataset and the most recent National Wetlands Inventory vector dataset (Office for Coastal Management, 2024; U.S. Fish and Wildlife Service, 2024). Agreement in the historical distribution of wetland among all three datasets was consistent. The added marsh type delineation in C-CAP and National Wetlands Inventory was ultimately deemed unnecessary given the lack of specific nesting site data, and NLCD emergent herbaceous wetland was the delineation used in this analysis. Several studies on eastern black rail locations note the importance of high marsh (Haverland and others, 2021; Stevens and others, 2022), and multiple recent datasets characterize this classification covering sections of the Atlantic and U.S. Gulf coasts using different methodologies (Allen and others, 2017; Correll and others, 2019; Enwright and others, 2022); however, this report uses a spatially consistent dataset (the NLCD dataset) to demonstrate the inundation risk across parishes and counties of interest.

For the scope of this report, we focus on coastal parishes and counties with possible, probable, or confirmed eastern black rail breeding activity post-2010, as listed in Watts (2016) and identified in figure 1. Additional parishes and counties with ocean-connected land 10 ft or less in elevation without recent reported eastern black rail activity are identified (U.S. Geological Survey, 2024). Ten feet was chosen because of the range of projected SLR available from the National Oceanic and Atmospheric Administration (NOAA) Sea Level Rise Viewer (National Oceanic and Atmospheric Administration, 2024). Six regions with recent breeding activity were selected to assess how SLR, high tide flooding frequency, and land cover distribution will affect historical habitat inundation across the range (fig. 1).

Relative Sea Level Rise and High Tide Flooding Levels

SLR is driven by changes in climate, and SLR scenarios follow from emissions scenarios; however, there is no direct one-to-one correspondence between a single emissions pathway used to discuss climate projections (for example, Shared Socioeconomic Pathway [SSP] 2–4.5) and a single scenario of SLR. Because of a combination of processes that may occur within several emissions scenarios and the inclusion of lower confidence processes related to ice sheets, SLR scenarios are assigned a level of probability of occurring under a given emissions scenario (fig. 2). In this report, we considered two SLR scenarios that bound the likely range of SLR for the moderate and high emissions scenarios (representative concentration pathway [RCP] 4.5 and 8.5, respectively) and the median of the 2050 extrapolation-based estimates of global mean sea level (GMSL); these SLR scenarios are the intermediate low (0.5 m of GMSL rise by 2100) and the intermediate scenarios (1 m of GMSL rise by 2100) (Sweet and others, 2018, 2022). The intermediate low SLR scenario has the greatest probability of occurring under an intermediate emissions scenario (for example SSP2–4.5 or RCP 4.5) when considering medium-high (dark yellow in fig. 2) and low (light yellow in fig. 2) confidence processes. Low confidence processes are Antarctic and Greenland ice-sheet processes with low agreement regarding rates, magnitude, and thresholds of change (Sweet and others, 2022). The intermediate SLR scenario has the greatest probability of occurring under a high emissions scenario (for example SSP5–8.5 or RCP 8.5) when low confidence processes (light red in fig. 2) are disregarded. The use of multiple scenarios allows for more comprehensive risk assessment, especially at end of century. The use of other SLR scenarios such as intermediate high (1.5 m of GMSL rise by 2100) and high (2 m of GMSL rise by 2100) will exacerbate risks detailed here because sea levels would rise more rapidly and to a higher point by 2100.

These SLR scenarios represent a single average value of GMSL, which is driven by thermal ocean expansion and contributions from melting ice; however, the true SLR experienced in a location—relative SLR—is driven by additional local processes, including subsidence or accretion of coastal land, land water storage, stereodynamic effects from shifting wind and ocean currents, and gravitational and deformation driven changes from ice-mass loss (Sweet and others, 2022). These processes occur across multiple scales and can cause sea level variability from year to year. Data are presented here for the projected relative SLR at 2100 under the intermediate low and intermediate SLR scenarios (figs. 3 and 4; Sweet and others, 2022) relative to the historical Mean Higher High Water in 2000. Figures for relative SLR at 2050 are available in appendix 1; however, users should be aware of the uncertainty in these projected levels (app. 1) and that a given sea level may occur sooner or later at a given location. Mean Higher High Water is set as the threshold that is exceeded by water levels about 50 plus or minus (±) 5 percent of the days per year at a location within the historical tidal epoch (1983–2001).

Relative sea level is calculated at tidal gages, but the density of gages differs across the coastline. The Interagency Task Force on Sea Level Rise developed a representation of relative sea level on a 1-degree grid to provide more even coverage across the coast, and this product is recommended when looking at scenarios in areas without a tidal gage (county scale or greater; Collini and others, 2022). We include relative sea level and high tide flooding days at the tidal gage locations (fig. 1). This is the scale at which the high tide flooding frequency data are available and provides consistency between this information and relative SLR scenarios. The uncertainty in relative sea level projections (19–52 centimeters [cm] between 17th and 83d percentile projections at 2100 depending on scenario and gage) is greater than that between the tidal gage relative sea level and closest centroid relative sea level at several locations (app. 1, table 1.2). Additionally, the NOAA Sea Level Rise Viewer recommends that users round to the nearest 1-ft increment when investigating SLR inputs because of the elevation and tidal surface measurement accuracy (National Oceanic and Atmospheric Administration, 2022).

As sea level rises, the occurrence of high tide flooding events will increase by a factor of 5 to 10 from 2020 to 2050 under the intermediate SLR scenario in all locations along the Atlantic and U.S. Gulf coasts (Sweet and others, 2018; May and others, 2023). This increase is concerning for eastern black rail given its vulnerability to flooding events during nesting and molting. High tides are driven by several factors including tidal cycles and will be altered by rising sea levels, changes in ocean circulation, and shifting wind patterns (Sweet and others, 2018). Year-to-year variability is expected given the uncertainty in these driving factors and tidal cycles and may result in rapid increases in high tide events and clusters of extreme events (Thompson and others, 2021). High tide flooding thresholds presented here are NOAA-derived thresholds based on a comparative analysis of tidal data across the United States (Sweet and others, 2018). High tide flooding thresholds are defined relative to their expected effect: minor (more disruptive than damaging), moderate (damaging), or major (destructive). Sweet and others (2018) developed a spatially consistent threshold: 0.5±0.19 m, 0.8±0.25 m, and 1.17±0.39 m for the three levels, respectively. Local variation of these thresholds is provided in appendix 1.

We examined the projected number of high tide flooding days at these local thresholds developed by Thompson and others (2021) between April and September (a total of 183 days) to assess the changing risk to the eastern black rail during the breeding season (Thompson and others, 2021). The median number of projected high tide flooding events during the breeding season (a sum of the median projected value for each month) for the minor, moderate, and major high tide flooding thresholds is presented at each of the eastern black rail gage locations under a range of SLR scenarios and time periods (figs. 5, 6, 7, and 8). Values bounding the very likely range of projected days are provided in appendix 1 (tables 1.3, 1.4, 1.5, 1.6, 1.7, and 1.8). Note that these uncertainty values do not include the uncertainty within the SLR scenarios themselves (Thompson and others, 2021). These data are available in the Flooding Analysis Tool (https://sealevel.nasa.gov/data_tools/15/), developed in collaboration with the National Aeronautics and Space Administration Sea Level Change Team and the University of Hawaii Sea Level Center using the 2022 relative SLR scenarios (Sweet and others, 2022) and methodology from Thompson and others (2021).

Marsh Resilience

The inundation analysis in this report assumes static distributions of marsh land cover from historical data products. In reality, marsh landscapes are projected to respond and adapt to climate-driven changes in a variety of ways (FitzGerald and Hughes, 2019). To assess potential changes in marsh availability because of SLR, we examine two marsh products. First is a relative marsh resilience score from the tidal marsh resilience to sea level rise analysis developed by the NOAA Office for Coastal Management and the National Estuarine Research Reserve System (Stevens and others, 2023). This score assesses drainage basins with estuarine marsh (based on C-CAP data) according to the current marsh characteristics (using 2010 data), vulnerability to SLR, and adaptive capacity. These rankings do not provide an objective assessment of marsh health and resilience (the drainage basins are ranked from 1 to 10 relative to each other), but they do allow assessment across the full coastal distribution of the eastern black rail (fig. 9).

The marsh migration data developed by the NOAA Office of Coastal Management and available in the NOAA Sea Level Rise Viewer is used as a component of adaptive capacity in the marsh resilience score described previously. This marsh migration dataset can be analyzed in isolation to give a second assessment of potential marsh migration rates under multiple SLR heights (app. 2). In the absence of localized numerical marsh modeling for the full range of eastern black rail, these products allow for a comparison of relative marsh resilience. However, they do not capture local factors such as sediment dynamics in the same way as a more detailed model (Fuller and others, 2011) and do not account for competing pressures like mangrove expansion (Bardou and others, 2023).

Eastern Black Rail Coastal Flooding Risk Under Sea Level Rise

Rising sea levels leading to more frequent and more extensive high tide flood events will lead to a larger area of potential eastern black rail habitat inundation. To compare the consequences of these two changes, we assess the percentage of inundated habitat areas defined using the NLCD dataset under 0–9 ft of SLR for representative counties in six distributed regions (figs. 10, 11, 12, 13, 14, and 15). These percentages can be contextualized by comparing to the two sets of thresholds discussed here: relative SLR in figures 3 and 4 and in appendix1 (tables 1.1–1.2; figures 1.1–1.2) and high tide flood thresholds for each region, which are marked with dotted lines in figures 10, 11, 12, 13, 14, and 15 and defined in appendix 1 (tables 1.3, 1.4, 1.5, 1.6, 1.7, and 1.8).

Inundation levels are rounded to the nearest foot, and this inundation analysis quantifies the percentage of wetland habitat affected. Note that, depending on the amount of initial marsh habitat, a county with larger inundation percentages may still have larger absolute areas of a given habitat available. In most cases, the inundation of the transitional zone is at or below the inundation of the more inclusive emergent herbaceous wetland area because of its distance inland.

Combining the drivers (relative sea level rise and high tide flooding), exposure (inundation), and adaptive capacity (marsh resilience) allows for an assessment of relative risk from high tide flooding across the coastal breeding range of the eastern black rail. For example, the counties analyzed in Texas will experience a higher rate of relative SLR than other analysis areas (figs. 3 and 4) and more frequent occurrence of high tide flooding events (figs. 5, 6, 7, and 8), but they will initially experience a relatively low level of habitat inundation, likely because of the location and elevation of marsh areas along the Texas coast (fig. 10). This area has a medium marsh resilience score (fig. 9) and the potential for additional marsh area (app. 2).

The counties analyzed in New Jersey will likely experience a relatively high level of SLR (figs. 3 and 4) and high tide flooding events (figs. 5, 6, 7, and 8) and a steep increase in the percentage of habitat inundated under even small increases in relative sea level (fig. 11). This inundation is coupled with lower relative marsh resilience (fig. 9) despite potential area for marsh to expand (app. 2).

The northern coast of North Carolina will experience a relatively high level of SLR (figs. 3 and 4) and high tide flood event frequency (figs. 5, 6, 7, and 8; similar to the counties in New Jersey). Although habitat inundation is initially low in North Carolina under 0–2 ft of SLR, there is a steep increase under higher rates (fig. 12). The multifactor analysis of marsh resilience described previously gives this area a relatively good score (fig. 9); however, an analysis of potential marsh expansion area alone indicates little room for movement (app. 2).

The South Carolina counties exhibit a similar steep increase in coastal wetland inundation to the counties in New Jersey (fig. 13) but lower relative SLR (figs. 3 and 4) and high tide flooding event frequency than some other regions like North Carolina, New Jersey, and Texas (figs. 5, 6, 7, and 8). This area has a high marsh resilience score according to Stevens and others (2023); however, migration analysis indicates the potential for expansion only under low levels of SLR with loss at higher levels (app. 2).

The counties analyzed in the two regions of Florida are projected to experience the lowest relative SLR by 2100 (figs. 3 and 4) along with comparatively fewer (though still substantially increasing) high tide flooding events (figs. 5, 6, 7, and 8). The eastern Florida Panhandle will see a high percentage of habitat inundation under low to moderate levels of SLR (0–4 ft; fig. 14). This region also has a high marsh resilience (fig. 9) and higher potential marsh migration area (app. 2). The southeastern coast of the Florida Peninsula faces the most unique situation of the regions, mainly because of dense existing development along the coast and marsh areas limited to interior areas of the counties. Projected emergent herbaceous wetland habitat inundation is steadily increasing with SLR in the case of Miami-Dade County, whereas Broward County is only affected at higher levels of SLR and Palm Beach County faces no inundation of historical emergent herbaceous wetland in our analysis because these areas are farther inland (fig. 15). Marsh resilience scores for these counties are medium but are constrained to the immediate coast (fig. 9), and a countywide analysis indicates potential for estuarine and brackish marsh migration in Broward and Palm Beach Counties (app. 2).

By the end of century (2100), the high tide flooding frequency projections indicate daily occurrence of high tide events at or above the historical minor threshold under the intermediate low and intermediate SLR scenarios for all coastal locations. Under the intermediate SLR scenario, the projected relative SLR in locations along the coast will meet or exceed even the major high tide flood threshold for most of the breeding season. The high tide flooding frequency data provide no insight about the maximum tidal level expected beyond this threshold and therefore provide little information about the true inundation levels experienced during extreme high tidal events in conjunction with SLR. For example, under 4 ft of relative SLR (the median projected SLR at 2100 under the intermediate scenario), a high tide flood event that contributes an additional 4 ft of inundation (an approximate major high tide flood threshold) would potentially contribute to a combined 8 ft of sea level depth above Mean Higher High Water. The analysis presented here can capture these events as meeting or exceeding the major high tide threshold of 4 ft but does not fully capture the habitat effect of the event. Therefore, analysis presented here includes potential SLR inundation amounts that exceed the historical high tide flooding thresholds and the projected base level of relative SLR, although the habitat percentages account only for historical wetland distribution. Additionally, storm surge and wave events will increase this inundation even further.

Adaptive Capacity

Eastern black rail traits may allow the subspecies to adapt to some of the effects of SLR and high tide flooding. Habitat analyses in this report rely on coarse habitat designation; the wetland and transition zone filters used to designate potential nesting areas in this report likely include lower marsh areas that eastern black rails would not select. Additionally, the 3-m resolution digital elevation models used to calculate SLR extent smooth out high points, eliminating some elevational heterogeneity, and have an average vertical root mean squared error of as much as 10 cm (National Oceanic and Atmospheric Administration, 2022). Nest site selection on elevated sites even 6 cm above the substrate (Legare and Eddleman 2001) or building nests on top of vegetation provides some additional distance from flooding; however, the rate of SLR and future high tide flooding are likely to exceed the elevational flood protection of many historical nest sites.

Latitudinal differences in breeding phenology are not evident (Watts, 2021); however, eastern black rails have been recorded to renest in a single season after a first failed attempt (Legare and Eddleman, 2001). The success rate and propensity to renest after nest loss are not known for the eastern black rail. Where quantified in Anas platyrhynchos (mallards; Linnaeus, 1758; Arnold and others, 2010) and Charadrius melodus (piping plover; Ord, 1824; Swift and others, 2020), reproductive success often decreases with multiple nest attempts in a year. This decrease in success is partially explained by generally lower success for later season nesting.

The eastern black rail does not only nest in the tidal wetlands that are the focus of this report but also in grassy fields and freshwater wetlands with no tidal influence and managed impoundments (Watts, 2016). SLR will have little to no effect on noncoastal wetlands, so they were excluded from this report that focuses on threats from saltwater inundation. Noncoastal wetlands may become increasingly important breeding areas as sea level rises, which has led some working groups to strategize creation of new nontidal, freshwater wetland habitat (Atlantic Coast Joint Venture, 2020; Watts and Beisler, 2021). Where studied, eastern black rail seems to preferentially use managed impoundments versus other wetlands (Roach and Barrett, 2015). Although we do not focus on coastal impoundments, they are largely captured as emergent herbaceous wetland in the NLCD 2021 dataset (Dewitz, 2023) used to delineate possible habitat. Low-lying hydrologically unconnected areas are captured in the SLR spatial data used in this report (National Oceanic and Atmospheric Administration, 2024). As inundation levels exceed barriers, these areas are inundated, but their representation depends on the detail available in the elevation data used to map inundation depth (National Oceanic and Atmospheric Administration, 2022).

This report does not consider the active role that management could play in protecting low elevation habitat or altering vegetation type and density in support of eastern black rail habitat needs and nesting in impoundments. These management approaches could be a method for maintaining or creating habitat for eastern black rails and other marsh species in the future (Roach and Barrett, 2015). Areas like the Florida Everglades may provide additional benefits for marsh resilience and nesting availability through broader landscape-scale restoration and conservation efforts.

Compounding Stressors and Marsh Migration

Human modifications to coastal and near coastal systems are likely to impede marsh migration and marsh resilience without careful planning; for example, coastal squeeze between modified landscapes and rising sea level is likely to inhibit coastal habitat migration, and this risk is largest around developed, densely populated coastal areas (Borchert and others, 2018). In our analysis, the potential ability of wetlands to migrate is captured using the tidal marsh resilience to sea level rise analysis developed by the NOAA Office for Coastal Management and the National Estuarine Research Reserve System (Stevens and others, 2023) and marsh migration data available in the NOAA Sea Level Rise Viewer (National Oceanic and Atmospheric Administration, 2024). However, these products incorporate only historical patterns of urbanization and agriculture and do not include how potential area available for marsh migration will change with future human development. Projected marsh distribution shifts will also be slow and variable across the coast as inundation and salinity changes modify these ecosystems over time (Field and others, 2016).

This report details thresholds and changes associated with SLR and high tide flooding events, but storm surge and inland flooding from heavy rainfall events can also endanger nesting sites. In several locations along the coast, historical surge events of 5–10 ft have been detected since 1880 (Needham and Keim, 2012). This report does not catalog historical surge events or project how they might change; however, potential surge inundation can be mapped with the inundation values presented in figures 10, 11, 12, 13, 14, and 15. Given the potential for renesting, this analysis focuses on the threat posed by increasingly frequent breeding season high tide flooding events driven in large part by SLR. Location-specific storm surge event frequency has not been projected given the uncertainty of landfalling hurricane frequency changes in the United States under various climate scenarios (Marvel and others, 2023). Inland freshwater flooding may pose issues to managed and unmanaged areas but is beyond the scope of this report, which focuses on the threat posed by saltwater inundation.

Conclusion

Laterallus jamaicensis jamaicensis (eastern black rail) are at greatest inundation risk during April–September when they inhabit coastal marsh areas for breeding and molting. They require wetland habitat for nesting but are unable to easily escape high water during breeding season. Some of these areas are currently affected by high tide flooding events, and the total area of coastal marsh expected to be affected by high tide flood events will increase because of SLR. This report investigates the change in days above historical high tide flood thresholds within this essential habitat for nesting eastern black rail. This approach does not capture some important processes to understanding the full effect to eastern black rail (such as fine scale microtopography variations, marsh evolution, coastal surge events, and management choices) because of data limitations regarding nesting preferences and habitat use. However, this study provides a qualitative assessment of coastal marsh inundation risk under a progression of SLR heights and incorporates the increasing frequency of days at or exceeding historical high tide flood thresholds across the eastern black rail’s coastal breeding range.

Parishes and counties across the eastern black rail breeding range will face variable risks from high tide flooding and relative SLR. Eastern black rail breeding habitat is more at risk in areas with less historical habitat, higher rates of relative SLR, and a larger area of low elevation habitat. In some parishes and counties, coastal habitat has already been lost to land use change, reflecting the historical habitat loss that led to current subspecies decline. The distribution of habitat across the coast and the elevational gradient of the region are important factors for determining the risk to SLR and high tide flooding for eastern black rail. The resilience of marsh systems and the potential for inland marsh migration, which is mediated by current and future land development, are key considerations for future breeding habitat availability for these and other coastal wetland species. Lastly, the assessment of historical habitat inundation may underestimate potential nesting habitat if management options are not modeled and considered in future occupancy estimates.