Crouching, Deirdre Robinson gingerly moves her hands around swirling tufts of grass, feeling for an increase in density. If she’s lucky, the grass will give way to reveal a woven canopy of grasses—under which will be a clutch of precious eggs.
“It’s like a eureka moment,” says Robinson, a co-director of the Saltmarsh Sparrow Research Initiative (SSRI), as she recalls the adrenaline rush of discovering a saltmarsh sparrow nest at Jacobs Point Salt Marsh in Narragansett Bay, Rhode Island.
With an orange-buff face and streaky brown and gray plumage, the saltmarsh sparrow has a tremendous burden—to survive and reproduce in the ever-changing interface of the tidal marsh. Found only along the Atlantic coast, it solely breeds in the salt marshes stretching from northern Virginia to Maine, constructing their nests in the grasses above the tide line. Depending on the whims of the tides, the nests could be inundated, sending the eggs swirling into the rush of water, and lost to the wetlands.
Saltmarsh sparrow chicks drowned after high tide at the Rachael Carson Reserve in Maine. Along the northeast coast of the U.S., seas are rising and making high tides like these more dangerous for young sparrows.
In their habitat, floodwaters rise higher than the sparrows’ nests about once every 28 days. This 28-day window allows the female sparrows just enough time to build their nests, lay their three to five eggs, incubate them, and then feed and protect the nestlings until they leave the nest at nine or 10 days old, just before their nests are flooded. The timing is so tight that the nestlings often climb to safety in the vegetation above the nest to avoid drowning at the time of peak tidal height.
The saltmarsh sparrow is now facing these fatally high tides more often, putting them in a precarious ecological spot. The Atlantic Coast’s wetlands are being swallowed by sea level rise, losing three millimeters of land per year in the last century. As a result, saltmarsh sparrows may soon be added to the endangered species list.
But even with such federal protections, scientists are merely trying to postpone their extinction. Studies predict that the species is doomed to vanish from its teeming, briny world as early as 2035 or 2050.
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“If the bird can’t complete its nesting cycle within the windows of opportunity between monthly peak tides, that triggers extinction. The higher the tides, the narrower the window for these birds to nest,” says Jim O’Neill, who along with Robinson, is a co-director of the SSRI, based in Rhode Island.
The disappearing salt marsh
With no shade under the beating sun, scientists wear chest and hip waders to walk through the soft, grassy contours of a marsh, watching for dangerous holes in the ground. If they step in the wrong spot, they risk sinking up to their waist in deep peat. Salt marshes contain layers of decaying plant matter and possess a characteristic rotten egg smell. Such a mixture of elements, it turns out, is essential.
Marshes protect the coastline from floods and storms, reducing shoreline erosion by blunting wave energy and fighting climate change by storing carbon. They’re also a shelter and source of food for commercially important species like shrimp and blue crab.
In the past two decades, 500 square miles of salt marsh have been lost around the world. In many cases, marsh grasses were harvested for hay or land was filled in for pasture and other uses.
In the 1930s, mosquitoes posed health risks to the peoples living near these wetlands, and the government set up programs to get rid of the standing water mosquitoes breed in by hand digging ditches in the salt marshes. Nearly 90 percent of salt marshes along the Atlantic Coast were grid ditched and inundated with so much water they began to degrade, destroying saltmarsh sparrow habitat.
Over the past decade, scientists have been trying to undo this work by digging drainage channels and rebuilding marsh land by filling them with sediment. Nancy Pau, a wildlife biologist at Parker River National Wildlife Refuge beams when describing how the rebounding marsh has benefited its winged inhabitants.
“Saltmarsh sparrows need to find that perfect spot to nest. Like Goldilocks. If the nest is too low, it gets flooded. If the nest is too high, it’s visible to predators.” Pau chuckles.
To study whether these restoration efforts are working, University of Connecticut ecologist Chris Elphick and his team put transmitters on birds to track how they use these sediment mounds. They also look for nests to see if the birds are using restored areas and if they are successful.
It’s too early to say if the birds are benefiting, and Elphick’s long term models still suggest a dire future in which populations fatally decline.
A new chapter in sparrow evolution
A bird must be tenacious and unrelenting to thrive in a tidal marsh. That’s why, says Adrienne Kovach, professor at the University of New Hampshire and SHARP researcher, saltmarsh sparrows have a suite of adaptations referred to as the saltmarsh syndrome.
“Their kidneys have adaptations like osmoregulation for dealing with the salty water they consume. Their plumage is also more melanistic. The most prevailing hypothesis is that the darker pigment provides the feathers some protection against degradation in the marsh. They also have larger bills than their upland relatives for thermoregulation in hot and humid environments,” she says.
The Nelson sparrow, a neighboring species, which nests slightly upriver, is less attuned to live in the salt marsh than the sparrow. Despite this difference, the birds are besotted with each other—transcending species to mate and hybridize naturally.
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By borrowing bits of DNA from the Nelson sparrow, its saltmarsh counterpart might be able to live farther upland. “It may allow an evolutionary spark for them to adapt,” says Logan Maxwell, research scientist at the University of New Hampshire.
If the saltmarsh sparrow was to go extinct, these new hybrids would be the only remaining pocket of their genetics. In a paleontological parallel, it’s similar to how Homo Sapiens interbred with now extinct Neanderthals, and portions of the Neanderthal genome are carried on in people today.
However, hybridization with the Nelson sparrow has consequences on their reproductive success—in lowland marshes, saltmarsh sparrows more successfully nest than Nelsons, and their hybrids fall somewhere in between.
SSRI has developed and is experimenting with a small structure called the “Nest Ark”, a wide-rimmed cup perched on the marsh’s peaty soils that rises and falls with the tides, holding the nest above the water level at all times.
Another solution might be to promote the growth of taller woody plants like high tide bush, providing nesting habitats that better withstand heightened tides. While the sparrows don’t currently select these tall grasses, the hope is that they one day might.
“If the birds build in or near it, their nests are elevated, which gives them a head start in avoiding flooding,” says Steven Reinert, a co-director at SSRI.
Back in Rhode Island, it is just before dawn and Deirdre Robinson is already out surveying, her pants tucked into her socks to keep the ticks away. As the marsh wakes up, she is still, her eyes darting around the grasses. Pale light illuminates dew drops on the spiderwebs, fiddler crabs scuttle around making burrows, and above her, a pair of ospreys swoop.
She hopes to see a mother sparrow scampering out from beneath her intricate grass canopy, moving with practiced stealth like generations of mothers before her, in search of sustenance for her young in an environment replete with food.
The saltmarsh sparrow is known colloquially as a “canary in the coalmine,” or an indicator species that reflects the overall health of the marsh.
Robinson pauses, looking solemn. “The sparrow tells us that there’s a problem with the salt marsh. It’s been telling us that we haven’t been listening. The warnings were always there.”
