Global & Local Importance of North American Tidal Marsh – Tidal marshes form the dominant transition zone between terrestrial and marine communities in eastern North America. The eastern North American coast alone possesses over one-third of the global extent of tidal marsh and the highest level of vertebrate biodiversity and endemism (those species found in one location and no where else) of any tidal marsh region worldwide. These wetlands are home to 83 breeding vertebrate species, 22% of which occur only in tidal marshes or possess subspecies found only in tidal marshes (Greenberg and Maldonado 2006). Tidal marshes are therefore primarily a North American resource, and it is a primary North American responsibility to conserve the ecosystem’s global flora and fauna.
Risk of Ecosystem Loss and Degradation – The global importance of and local services provided by tidal marshes may justify their preservation, but it is their high risk of degradation and loss that is the call for conservation action. Tidal marshes compete for space with (and are downstream of) some of the continent’s most highly developed areas. This leaves the ecosystem open not only to outright loss, but also to the severe degradation of all remaining habitat. Along the highly developed eastern U.S. seaboard, tidal marshes are found at the mouths of some of the country’s most human-impacted drainages (e.g. the Susquehanna, Delaware, Hudson, and Connecticut Rivers) and along the shipping routes of some of the busiest ports (e.g. Norfolk, Baltimore, Philadelphia, New York, and Boston). There are no pristine tidal marshes left in this region. By the late 20th century, 90% of northeastern salt marshes had been ditched for mosquito control to some degree (Daiber 1986).
Tidal marshes are also threatened by sea-level rise. Over the last century sea level has risen ~2 mm/year (although local effects vary: Douglas 1991), and this change has altered marsh vegetation and caused marsh loss across the Atlantic seaboard. Sea-level rise is projected to accelerate over the next century with predicted tidal marsh losses of 0.5-1.5% each year (Greenberg 2006). Small sea-level increases could push tidal marsh bird populations to a threshold beyond which rapid declines are likely.
Risk of Species & Endemic Population Loss – Many organizations recognize these risks as threats to tidal marsh birds. Two species are “red-listed” by the International Union for Conservation of Nature (IUCN); six are on the American Bird Conservancy/National Audubon Society’s Watch List; and 10 are considered priority species by Partners In Flight. Overall, 26 bird species that breed in or use these habitats during the breeding season are listed as “Species of Greatest Conservation Need” by states along the eastern seaboard of the United States.
The State of our Knowledge –
- Marshes from New Jersey to Virginia support greater abundances of Species of Greatest Conservation Need (SGCN) relative to the smaller marshes of New England and New York, including Clapper Rail, Willet, American Black Duck, Saltmarsh Sparrow, and Seaside Sparrow.
- The density of some species (e.g., Saltmarsh and Seaside sparrows) is highest in the north, however, and marshes in New York and New England support approximately 30% of the global breeding population of Saltmarsh Sparrows.
- Black Rail detections are too infrequent (10 detections over two years of surveying) to estimate abundance or trends, despite call-back surveys across USFWS Region 5, indicating a complete collapse of these Mid-Atlantic populations.
- On average, tidal-marsh specialists have declined across New England and USFWS Region 5 as a whole from 1994 – 2012.
- For Saltmarsh Sparrows, these declines are most severe on marshes with tidal restrictions, although the trend remains across all tidal marsh specialists even when excluding Saltmarsh Sparrow.
- Within Connecticut (the only state where historical nesting data have been analyzed), nest density is also declining for Saltmarsh Sparrows, Seaside Sparrows, and Clapper Rail, with Saltmarsh Sparrows showing the strongest decline. The declines are consistent with increases in rates of nest flooding since 2002.
- Seasonal reproductive success (incorporating nest success and renesting rates) for Seaside Sparrows generally declines from south to north within USFWS Region 5 (Virginia to Maine), and Nelson’s Sparrow reproductive success is highest at the farthest upriver marshes.
- Saltmarsh Sparrow seasonal reproductive success is highly variable across their range and is driven more strongly by local rather than regional patterns. Nests across the range are equally likely to be flooded, but nest predation rates increase to the south.