Saltmarsh Restoration and it’s Consequences for Tidal Marsh Birds
Franco Gigliotti and Chris Elphick | University of Connecticut
frank.gigliotti@uconn.edu
This presentation begins at 2 hours 24 minutes on the video recording of the conference: COA's Birds and the Environment Science Conference - Online - YouTube
Saltmarsh ecosystems are changing, with increased evidence of wetter conditions and marsh loss as sea levels rise [1]. Less than 50% of the historical extent of saltmarshes persists world-wide [2], with declines in extent averaging 0.4% per year in coastal New England, USA [3]. Breeding bird species that depend on these ecosystems are suffering as a result, with well documented declines throughout the northeastern USA since at least the 1990s. For example, three-quarters of the global saltmarsh sparrow Ammospiza caudacuta population was lost between the 1990s and early 2010s, with the species predicted to go extinct mid-century [4, 5]. Substantial conservation efforts are underway to improve the status of this species and other saltmarsh-nesting birds, and to avoid the future need for multiple species listings under the US Endangered Species Act (ESA). Given the rapid observed and predicted declines of tidal marsh extent in the northeastern USA, restoration activities will be a large and necessary component of conservation efforts.
Thin layer placement (TLP), the application of sediment to drowning tidal marshes to raise the elevation and improve habitat, has garnered the interest of multiple agencies working in the Northeast as a focal restoration tool. Multiple TLP projects are currently underway in the tidal marshes of southern New England, and it is essential to understand the outcome of these restoration actions – which can cost millions of dollars [6] – to determine whether funds are being used effectively and providing intended benefits to target species such as the saltmarsh sparrow. TLP could improve saltmarsh sparrow habitat by raising tidal marsh elevation and converting areas of wetter, low marsh to drier, high marsh. Saltmarsh sparrows require high marsh habitat for breeding, and nest flooding is a primary driver of population decline that will only increase in relevance as sea levels continue to rise [7]. Desired benefits of restoration will only be realized, however, if the following assumptions are correct: 1) Patches of tidal marsh where TLP is applied regenerate high marsh vegetation suitable for saltmarsh sparrow nesting. 2) Saltmarsh sparrows modify their nest selection behavior in response to TLP, and nests located within restored areas are successful. 3) TLP restoration does not reduce the short-term nest success of saltmarsh sparrows by temporarily removing suitable habitat from the landscape through sediment addition. Our study will test these assumptions.
We will conduct this study at tidal marsh sites in coastal Connecticut. Experimental sites (e.g., Great Meadows Marsh, Stratford; Sluice Creek, Guilford) will receive TLP application through ongoing restoration work conducted by management agencies. These marshes are known to harbor saltmarsh sparrows, but only limited baseline data pertaining to nest density or success is available. In recognition of this limitation, we will also sample reference sites (e.g., Hammonasset Beach State Park, Madison; East River Marsh, Guilford) that are known to represent suitable nesting habitat and where we have been collecting sparrow breeding data since 2002. Restoration at experimental sites have been approved and implementation is imminent.
We will collect two years of data from a focal area within each sampled marsh to understand variation in saltmarsh sparrow nest site selection behavior and space use, as well as vegetation regeneration following TLP application. Surveyed areas at experimental sites will contain both the restored areas and unrestored habitat to serve as a control for comparison. We will address assumption (1) by monitoring the response of vegetation post-TLP. During August 2021 (pre-restoration), we surveyed vegetation at all sites to describe baseline conditions. We will repeat these surveys during 2022 and 2023 (post-restoration) to track changes to the vegetation community and determine the consequences for suitable nesting habitat available to saltmarsh sparrows. We will address assumptions (2) and (3) by conducting weekly surveys at each site to search for nests and track their fates. These data will allow us to compare nest success and placement between control and restoration areas within experimental sites, and to relate nest metrics in these areas to reference sites. Vegetation sampling and nest monitoring will follow existing protocols, developed and tested over the past 10 years [8, 9].
To further understand the relationships between nest site selection, habitat availability, and space use, we will capture adult saltmarsh sparrows with mist-nets and affix small transmitters that allow us to track each bird’s movements after release. We will place electronic receivers at both experimental and reference sites to collect real-time movement data of tagged adults. We will use triangulation data from these tags to understand how sparrows use habitat at both experimental and reference sites providing new insight into how nesting sites are selected, how these decisions change as areas re-vegetate post-restoration, and whether TLP applications have negative repercussions for the birds’ daily activities.
Data collected from this study will directly inform tidal marsh conservation efforts at our Connecticut study sites, and throughout the global range of the saltmarsh sparrow, which spans the northeastern USA. Understanding the impacts of TLP on saltmarsh sparrow populations will allow state, federal and nonprofit conservation group stakeholders to better plan restoration activities. If benefits through increased nest success are realized through TLP application, the method may continue to be employed as a restoration strategy for saltmarsh sparrows. If impacts of TLP on saltmarsh sparrow populations are found to be detrimental to population growth, understanding the impacts and potential for mitigation before populations decline to the point where the species is on the cusp of extinction will be essential, as application of the technique would be both costly and counter to the goals of recovering the species. With an ESA listing decision set to occur by 2024, results gained from this study will be of value to all organizations ultimately tasked with recovering saltmarsh sparrow populations.
Literature Cited
1. C. R. Field, C. Gjerdrum, C. S. Elphick, Forest resistance to sea-level rise prevents landward migration of tidal marsh. Biological Conservation. 201, 363–369 (2016).
2. C. J. Mcowen et al., A global map of saltmarshes. Biodivers Data J, e11764 (2017).
3. E. B. Watson et al., Anthropocene survival of southern New England’s salt marshes. Estuaries Coast. 40, 617–625 (2017).
4. C. R. Field et al., High-resolution tide projections reveal extinction threshold in response to sea-level rise. Global Change Biology. 23, 2058–2070 (2017).
5. C. R. Field et al., Quantifying the importance of geographic replication and representativeness when estimating demographic rates, using a coastal species as a case study. Ecography. 41, 971–981 (2018).
6. M. Myszewski, M. Alber, Use of Thin Layer Placement of Dredged Material for Salt Marsh Restoration. Georgia Coastal Research Council, University of Georgia, Athens, GA. p 45 (2017).
7. T. S. Bayard, C. S. Elphick, Planning for sea-level rise: quantifying patterns of saltmarsh sparrow (Ammodramus caudacutus) nest flooding under current sea-level conditions. The Auk. 128, 393–403 (2011).
8. K. J. Ruskin et al., Seasonal fecundity is not related to geographic position across a species’ global range despite a central peak in abundance. Oecologia. 183, 291–301 (2017).
9. B. Benvenuti et al., Plasticity in nesting adaptations of a tidal marsh endemic bird. Ecology and Evolution. 8, 10780–10793 (2018).
