Photo: Jim O'Neill
Salt Marsh Life
Salt Marsh Cycles
Salt marshes are habitats that are pulsed by two high tides and two low tides during each 24-hour cycle. The height of a given high tide is influenced by the phases of the moon as well as the wind. During any monthly cycle, peak tides occur during those lunar phases when the sun and moon align with the earth (i.e. during, full and new moons) and the combined gravitational pull of those bodies on the earth’s oceans is at its greatest for that cycle. The relatively high-amplitude tides associated with those lunar events are called “spring” tides (no seasonal connotation). Further, twice a year a “king tide” causes especially extreme fluctuations in water levels when the earth and moon pass more closely to each other than normal. Extended periods of flooding of tidal wetlands is becoming an increasing problem as sea level increases, and further, marshes are encroached upon by shoreline development with no place for the higher tidal waters to disperse. For detail on how spring tides affect the reproductive success of Saltmarsh Sparrows, please see our 2017/2018 Interim Results Report, and the Related Links page.
Salt Marsh Sparrows are not unique in struggling to survive in such a challenging environment. The closely related Seaside Sparrow has diminished dramatically in numbers in Rhode Island over the past four decades (see Berry et al. 2015). Clapper Rails were common members of Rhode Island’s salt-marsh nesting avifauna in the early 1980s, but are rarely seen in RI currently. However, the large sandpiper, the Willet, joined the salt-marsh-breeding-bird community during the mid-1980s and their populations are holding their own if not on the rise. Osprey are now common across much the eastern US and are an example of successful wildlife management in the last 50 years. This large bird of prey was one of the species devastated by DDT poisoning from pesticides. The buildup of this toxin in fish (their main food) led to a thinning of their eggshells which caused premature breakage. The turn-around came after the public outcry about the widespread use of pesticides during the late 1960’s and 1970’s. As natural nest-sites have become less common, many Osprey depend upon constructed nest platforms erected by conservation groups or private citizens. Another victim of habitat loss in the marsh is the Diamondback Terrapin, known for its distinctly marked shell and its dependence on tidal marshes. It was once hunted as a delicacy in the northeast, but today the main enemy is the destruction of nesting grounds. These turtles can only survive in brackish areas and need large areas of sandy embankments to lay their eggs. As the acreage of such embankments is reduced by development and rising water levels—and as tidal marshes, which the turtles rely on year-round for survival—are threatened by sea-level rise, the future of this reptile is in danger. Terrapin, and other salt-marsh wildlife, also face increased pressure from predators which thrive in proximity to humans. For details on the Barrington, RI population of Diamondback Terrapin, as documented by the Barrington Land Conservation Trust which manages the population, please visit http://blct.org/blct/terrapin-research/.
It is hypothesized that one major reason Saltmarsh Sparrows have selected such a seemingly inhospitable habitat is to avoid micropredators, such as parasites, which are less abundant in salt marshes than in adjacent non-wetlands. Yet, macro-predators such as coyotes, raccoons, opossums, rats, and foxes are posing an increasing risk since they forage in marshes and will consume anything from fish and invertebrates to the nestlings and eggs of nesting birds—including populations in peril such as Saltmarsh and Seaside Sparrows, and Clapper Rails. These predators were part of the marsh life-cycle historically, yet their numbers have increased disproportionally as they exploit the advantages of living near humans. Marsh-nesting birds are also at risk from avian predators as herons, egrets, gulls and harriers.
For more on salt-marsh life, please see our Related Links page.
The Saltmarsh Habitat & Avian Research Program (SHARP) is a group of academic, governmental, and non-profit collaborators gathering the information necessary to conserve tidal-marsh birds. The SHARP program provides a consistent platform for monitoring the health of North America’s tidal-marsh bird communities and the marshes they inhabit in the face of sea-level rise and upland development. SALSri coordinates closely with SHARP scientists in forming research goals—goals which are informed by these fundamental SHARP findings:
Tidal marshes are primarily a North American resource, and it is a primary North American responsibility to conserve the ecosystem’s global flora and fauna.
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 of any tidal marsh region worldwide.
These eastern North American wetlands are home to 17 breeding vertebrate species which occur only in tidal marshes or possess subspecies found only in tidal marshes. On average, tidal-marsh specialists have declined across New England from 1994 – 2012.
Marshes in New York and New England support approximately 30% of the global breeding population of Saltmarsh Sparrows.
Tidal marshes are significantly threatened by sea-level rise which is projected to accelerate over the next century with predicted tidal marsh losses of 0.5-1.5% each year. Small sea-level increases could push tidal marsh bird populations to a threshold beyond which rapid declines are likely. Within Connecticut, nest density is diminishing for Saltmarsh Sparrows, Seaside Sparrows, and Clapper Rails, with Saltmarsh Sparrows showing the strongest decline. These declines are consistent with increases in rates of nest flooding witnessed since 2002.
SALSri supports SHARP-consistent conservation goals.
Photo: Steven Thompson