This story was produced through a partnership with Climate Central, a non-advocacy science and news group. John Upton and Kelly Van Baalen of Climate Central contributed reporting.

SCARBOROUGH, Maine — A little brown bird with orange facial markings led Andrew Mackie to travel hundreds of miles from his home state of New York to Scarborough Marsh 30 years ago.

The avid birder came to see the saltmarsh sparrow, a secretive creature about 5 inches long and weighing half an ounce. It breeds in salt marshes from Maine to the Chesapeake Bay, nesting in saltmeadow cordgrass just above the high tide line and the ocean waters that rise up twice a day. Its hardiness and elusiveness attracted Mackie.

“It tends to be a skulker down in the salt marsh, so it’s not coming up to sit on telephone lines,” said Mackie, now the executive director of the Scarborough Land Trust. “You have to be a real bird lover to want to find that bird.”

The saltmarsh sparrow, which attracts birdwathers from afar, also is an indicator of the health of Scarborough Marsh. Its populations have been decreasing in recent years and the sea level has been rising. Credit: Courtesy of the U.S. Fish & Wildlife Service

The saltmarsh sparrow is more than a rarity for intrepid birders. Its presence indicates that the marsh is healthy, a home to wildlife, a place to recreate and hunt and a buffer against pollution and storm surge. Rising seas are threatening the marsh, and in turn, the saltmarsh sparrow. Their numbers are declining, with only about 1,600 of them left in Maine, which has prompted a state preservation effort.

But the broader race to save the 3,200-acre Scarborough Marsh — Maine’s largest contiguous salt marsh — is running into the twin challenges of rising seas and high development in the fast-growing Portland suburban area, giving the marsh little room to expand and putting it at risk of shrinking.

Salt marshes comprise less than 1 percent of Maine’s land area, mainly in the southern part of the state, but their value is extensive. They protect adjacent land and buildings from ocean flooding during storms. They absorb carbon and filter sediments and pollutants from water. They are hunting and fishing grounds, a recreation area and nurseries for fish and other animals.

Three people run along a trail through a marsh in the morning.
Three men run down the Eastern Trail, through the Scarborough Marsh, in Scarborough Thursday morning, July 21, 2022. The marsh’s future is threatened by climate change. Credit: Troy R. Bennett / BDN

Since colonial times, Maine has lost an estimated one-fifth of its wetlands to development and farming. While regulatory protections have stemmed those losses, the critical habitat faces new threats as sea-level rise accelerates and overtakes its seaward side.

Maine’s four-year climate action plan recommends that the state commit to managing at least 1.5 feet of sea-level rise by 2050 and 3.9 feet by 2100. A 1.5-foot rise could submerge 67 percent of Maine’s coastal sand dunes and reduce the dry beach area by 43 percent, significantly impacting coastal tourism, a major economic driver here.

Marshland is also threatened by the effects of heat-trapping pollution, even though it can grow vertically and migrate inland as seas rise. Scarborough Marsh already has some areas that show where such inland migration has overtaken old forests and led to “ghost forests,” stands of dead trees killed by saltwater.

Natural growth such as roots and above-ground plants add biomass to build the marsh up every year, helping it fight against sea water incursion. But rising seas can outpace the ability of marsh plants to keep up. Buildings, roads and other infrastructure also block a marsh’s ability to migrate.

The reflection of a passing truck is shown in the water of a marsh.
A truck drives down Route 9, next to the 3,200-acre Scarborough Marsh, in Scarborough on Thursday morning, July 21, 2022. Climate change, and its accompanying sea level rise, threaten both the marsh and the road. Credit: Troy R. Bennett / BDN

Scarborough Marsh faces such challenges. The area around it is highly developed with houses and commercial buildings. Roads and other obstacles hinder water flow. The dearth of open land for migration means it is unlikely for even aggressive conservation efforts to keep up with the rising tides, Mackie said.

A recent analysis by Climate Central, a non-advocacy science and news group, showed that halting coastal development and aggressively reducing pollution could limit coastal wetland losses in the continental U.S. to 10 percent this century. With ongoing coastal development and high sea-level rise, on the other hand, three quarters of marshland could be lost during the same timeframe.

Here in Cumberland County, where marshes are already ringed by neighborhoods and roads, Climate Central’s analysis showed efforts to conserve undeveloped land could see the total marsh area grow by 24 percent by 2100 even if seas rise rapidly. Aggressive development alongside rapid sea-level rise, by contrast, could cause 14 percent of the marsh area to be lost.

Conservation groups and the state’s fish and wildlife department often purchase land to open up pathways for marsh migration. However, the sparse land that might be available to buy from private owners is expensive because it is near the ocean. Mackie said the land trust has identified five parcels that it is looking to buy that average 15 acres each.

“There’s not a lot of undeveloped land around because the marsh is hemmed in by development,” Mackie said. “We and our partners have identified some parcels we would like to buy.”

Parcels will be recontoured to a higher elevation suitable for salt marsh formation, he said. Some communities plan to build sea walls to prevent flooding, but that strategy can be counterproductive around a marsh, which acts like a big sponge to absorb water.

White sea birds wade in the waters of a marsh
A group of egrets stand in the Scarborough Marsh in Scarborough Thursday morning, July 21, 2022. The marsh’s future is threatened by climate change. Credit: Troy R. Bennett / BDN

At the same time, the land trust is sensitive to the need for housing and development during a national housing crisis that Maine has experienced most in populated southern areas.

“Our position is that we need balanced growth with protecting our natural lands and resources that are critical to our livelihood, our sustainability,” Mackie said.

The Maine Department of Inland Fisheries & Wildlife, which owns a total of 110,000 acres across Maine with 60 different wildlife management areas, would be a major partner in land purchases. It owns 269 tidal marshes totaling 22,372 acres across the state. Of those, it owns and manages more than 95 percent of Scarborough Marsh.

When it looks at property, the department considers species, public access and connectivity of the habitat so aquatic species can move through it, Bethany Atkins, land acquisition and habitat grants biologist at the department, said.

“We only work with landowners who want to sell to us,” she said.

Since it will be a challenge to buy enough land for migration, the best scenario is the marsh surface keeping up with the rise of the sea, said Steve Pinette, president of the Friends of Scarborough Marsh, which also has identified several 10- to 20-acre parcels that should be purchased.

A drive up coastal Route 1 gives a glimpse of the issues the marsh faces. A section of the road, which runs through the western part of the marsh, floods frequently during astronomical high tides and prevailing winds, Jami Fitch, sustainability coordinator with the town of Scarborough, said. Some 30,000 vehicles travel on Route 1 daily, making the flooding a serious concern for the town and the state.

Parts of Route 1 and Route 9, another busy road perpendicular to it and running east-west through the marsh, are being prioritized by the town and state for possible elevation. Farther south, one road near the Rachel Carson National Wildlife Refuge in Wells might be left for that marsh to take over.

“These are the things we’re willing to consider,” Scarborough Town Manager Thomas Hall said. “We’ll either make major investments to reconstruct areas or let them go back to nature.”

Development doesn’t have to happen right on the edge of the marsh for it to have an impact, Hall said. Stormwater must be monitored carefully and chemicals going into rivers that feed into the marsh must be minimized, including lawn fertilizers.

The biggest challenge for the marsh’s longevity is addressing tidal flows and making them as natural as possible, Ryan Robicheau, wildlife management supervisor at the Maine Department of Inland Fisheries & Wildlife, said. The department is starting an assessment to understand the factors that play into the health of the marsh and prioritize funding over the next three to five years.

If the marsh is inundated with too much sea water, it could start converting to open water or a mudflat, state marine geologist Peter Slovinsky said. The nature of the marsh also could change. More of it could turn into the low marsh on its seaward side that floods more frequently, displacing habitat, including saltmarsh sparrow nests.

Boats sit idle in the waters of a marsh in the morning.
Boats sit on their moorings in Scarborough’s Nonesuch River, on the edge of a 3,200-acre marsh on Thursday morning, July 21, 2022. The marsh, home to abundant bird life, is threatened by climate change. Credit: Troy R. Bennett / BDN

Slovinsky said the marsh is a natural rearing ground for a variety of commercial fish, including cod. The small fish are eaten by birds and larger fish like migrating striped bass, bluefish and flounder.

“The marsh is intrinsically linked to the food web,” he said. “And the economic vitality of the community is only going to be as good as its environmental vitality,” he said.

Like many who spend time there, Pinette of Friends of Scarborough Marsh has developed a visceral connection to the marsh, one that contributes to its inherent value.

“In certain parts of the marsh you hear nothing, and you are surrounded by plants and trees,” he said. “It could be like it was in colonial days.”