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Report on the Current Conditions for the Saltmarsh Sparrow (Ammospiza Caudacuta)

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Report on the Current Conditions for the Saltmarsh Sparrow (Ammospiza Caudacuta) Report on the Current Conditions for the Saltmarsh Sparrow (Ammospiza caudacuta) U.S. Fish and Wildlife Service August 2020 1 Suggested citation: U.S. Fish and Wildlife Service. 2020. Report on the current conditions for the saltmarsh sparrow. August 2020. U.S. Fish and Wildlife Service, Northeast Region, Charlestown, RI. 106 pp. Cover: Saltmarsh Sparrow (photo credit: Evan Lipton) 2 Executive Summary This report describes the species needs, threats, and current conditions for the saltmarsh sparrow. It is intended to reinforce and support conservation planning for this species by the U.S. Fish and Wildlife Service (Service) and partners. As conservation measures are tested and implemented, the Service intends to expand this report to include an assessment of future conditions that reflects the effectiveness of on-the-ground implementation measures to slow or reverse saltmarsh sparrow population declines. The saltmarsh sparrow (Ammospiza caudacuta) is a tidal marsh obligate songbird that occurs exclusively in salt marshes along the Atlantic and Gulf coasts of the United States. Its breeding range extends from Maine to Virginia including portions of 10 states. The wintering range includes some of the southern breeding states and extends as far south as Florida. Nests are constructed in the salt marsh grasses just above the mean high water level, and they require a minimum of a 23-day period where the tides do not reach a height that causes nest failure. Across its range, the saltmarsh sparrow is experiencing low reproductive success, due primarily to nest flooding and predation, resulting in rapid population declines. Forty-eight percent of nests across the breeding range failed to produce a single nestling from 2011 to 2015. Although it has not been quantified, there is strong evidence for range contraction at both the northern and southern limits of the breeding range. Furthermore, breeding individuals are not evenly distributed across the entire range, with approximately 78 percent of the breeding population breeding in marshes of the mid-Atlantic states. At the northern end of their range, saltmarsh sparrows hybridize with the closely related Nelson’s sparrow (Ammospiza nelsoni subvirgata). Nelson’s sparrows are considered marsh generalists, occupying more brackish and inland marshes than the specialist saltmarsh sparrow, although both species can occupy the same patches in salt marshes in Maine and New Hampshire. Hybrid individuals may be able to occupy a wider range of habitat types that may not be impacted by sea-level rise at the same rate as tidal marshes. However, the extensive literature on hybrid populations suggests hybrid individuals typically have lower nest success than pure-saltmarsh sparrows, and that the two species are remaining distinct. While the species still occupies the majority of its historical range, the number of individuals within the breeding range has significantly declined since 1998. Based on surveys in 2012 the population was estimated at 60,000 individuals, having declined at an average of 9 percent per year across the range since 1998. Projecting those declines through 2020 we estimate that the current populations is approximately 28,215 individuals. This represents a decline of 87 percent from the 212,000 individuals estimated in 1998. Numerous threats have been identified as impacting the saltmarsh sparrow and/or its habitat. We assessed the following threats acting on the saltmarsh sparrow: (1) habitat loss, fragmentation, and degradation; (2) the effects of climate change; (3) hybridization; (4) predation; (5) contaminants; and (6) other factors influencing the species such as disease and altered food webs. Tidal marshes across the Atlantic coast are being lost or degraded at a rapid rate due to a combination of historic and on-going direct anthropogenic impacts (e.g., development, ditching, 3 shoreline hardening, etc.) and the impacts of sea-level rise. Range-wide loss and degradation of tidal marsh habitat has resulted in smaller, more fragmented habitat patches, as well as a disproportionate loss in suitable nesting habitat for the saltmarsh sparrow. Site specific rates of habitat loss have been correlated with multiple localized factors, including nutrient input from agricultural and urban runoff, shoreline hardening, geomorphic setting, tidal range, and presence of invasive plants or animals. Although our understanding of how these variables interact, exacerbate, or ameliorate habitat loss is less understood, we have concluded that these factors do influence how resilient a marsh is or will be to the impacts of sea-level rise. In addition to habitat loss, the frequency and duration of marsh flooding across the species’ range has also directly impacted reproductive success for the species. This has been attributed primarily to sea-level rise, but also increased precipitation and storm intensity during the breeding season as a result of climate change. While flooding impacts the breeding range uniformly, predation exerts a greater impact on the southern portion of the breeding range. We found little certainty for the potential additive impacts of hybridization, disease, altered food webs, environmental contaminants, adult or juvenile mortality during migration, or mortality on the wintering range. After review of the threats, we identified low reproductive success, and the loss of high marsh nesting habitat, as the two primary threats to the viability of the species. Both of these threats are driven primarily by sea level rise and exacerbated by historic and ongoing anthropogenic impacts. We also summarize existing conservation policy and management practices which are currently affording some level of protection for the species. These include tidal marsh land ownership, federal and state laws, habitat restoration and protection activities, and conservation planning tools under development. We were not able to compile a comprehensive list of recent conservation actions to quantify the number of acres protected or restored. We also do not have an assessment of what would be required to achieve population level benefits to saltmarsh sparrow. There are efforts underway to compile this information but it was not available for this report. The final section of this report evaluated the saltmarsh sparrow’s current condition based on our previously described evaluation of the species’ needs and the threats facing individuals and their habitat. This evaluation incorporated an assessment of the species’ population resiliency and species redundancy and representation. Resiliency metrics that were evaluated using the best available scientific information include habitat quality and quantity (i.e., total marsh habitat, marsh size, and availability of high marsh), population demographics (i.e., adult and juvenile survival, nest success and survival), and habitat alterations (i.e., human marsh alterations, development, and tidal restrictions). These factors were assessed within each of four analytical units across the species range. Three analytical units were identified in the breeding range (Northern, Central, and Southern) and one analytical unit in the wintering range. The units were defined based on variations in salt marsh habitat characteristics, tidal regimes, rates of sea-level rise, and other factors influencing saltmarsh sparrows and their habitat. To look at redundancy, we evaluated the species’ distribution across its entire range. Although the species continues to generally occupy the majority of its historic range, the species is unevenly distributed with a large concentration of its breeding individuals in a relatively 4 small geographic area. During the winter months the population is also concentrated within a similarly compressed geographic area along the southern coast. As such, the population is susceptible to catastrophic events such as major storms or hurricanes, so we determined that the redundancy for the saltmarsh sparrow is moderate. Representation for the saltmarsh sparrow is described as its ability to adapt to changing environmental conditions. There is some evidence that adult female saltmarsh sparrows will respond to nest loss by modifying the placement of subsequent nests to balance the trade-offs between flooding and predation (i.e. vary height within vegetation or proximity to the upland). Although saltmarsh sparrows exhibit this behavioral adaptation, the species has limited adaptive capacity with regard to nesting habitat characteristics. Nesting continues to be restricted to the high marsh area with few exceptions, and sea-level rise appears to be occurring at a rate that is faster than the species has been able to adapt based on the currently available information. We also conclude that hybridization is not presently providing any additional adaptive capacity for saltmarsh sparrows. As a result, we classified the saltmarsh sparrow as having low representation. Resiliency for the saltmarsh sparrow is its ability to withstand stochastic events. Based on recent population declines and low nesting success as well as increased impacts to its habitat, we have determined that the resiliency of the species for the Southern and Central analytical units within the breeding range is low. Within the Northern breeding analytical unit, which supports 13 percent of the breeding population, and in the wintering range resiliency is moderate. 5 [This Page Intentionally Left Blank] 6 Table of Contents INTRODUCTION.........................................................................................................................9
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