Protection of the nesting grounds of the Cape Sable seaside sparrow have been controversial in recent years, as efforts to keep some areas of the Everglades dry enough for sparrows – who nest low to the ground – conflict with the goal to send more fresh water south through the Everglades to Florida Bay.
A new study predicts sea level rise will make it even more difficult to maintain habitat suitable for the tiny birds in the Everglades.
Sea level rise may pose conservation challenges for the endangered Cape Cable seaside sparrow, by Stephanie Romanach, Saira Haider and Allison Benscoter, of the U.S. Geological Survey Wetland and Aquatic Research Center in Fort Lauderdale, was published in the January 2023 edition of Frontiers in Ecology and Evolution.
Florida’s Everglades is a wetland ecosystem that is host to many species, including a large number of endangered and endemic species, the authors explain. The endangered Cape Sable seaside sparrow (Ammospiza maritima mirabilis) nests in marl prairie habitat at the southern end of the Everglades. The locations of three of the six subpopulations are near the coast. “We found that the probability of sparrow presence decreased with increasing sea level rise. Within approximately 50 years, probability of presence significantly decreased for all three coastal subpopulation areas,” they explain.
One of the goals of the Comprehensive Everglades Restoration Plan (CERP) is to increase the dry season freshwater flow to Everglades National Park and Florida Bay. Increasing freshwater flow will also help combat the impacts of sea level rise on coastal ecosystems. However, restoring freshwater flow through the Everglades could negatively impact the marl prairie habit of the sparrows.
According to the National Park Service (NPS) web site, the sparrows nest in dense, clumped grasses. The sparrows tend to avoid tall, dense, sawgrass-dominated communities, spike-rush marshes, extensive areas of cattails, wetlands with tall, dense vegetation, and areas of woody vegetation.
Cape Sable seaside sparrows were first sighted in freshwater and brackish marshes on their namesake Cape Sable in Monroe County. In the 1930s, Cape Sable was the only known breeding area for the sparrows, according to U.S. Fish and Wildlife Service. The hurricane of 1935 is believed to have changed the habitat on Cape Sable from one dominated by freshwater plants to one dominated by saltwater plants. Changes in water flows due to upstream water management practices and another hurricane in the 1960s are also believed to have contributed to the sparrows’ loss of their original habitat. In 1967, the sparrows were given federal status as an endangered species. In 1977, they were put on the critical habitat list.
According to “Progress Toward Restoring the Everglades, the Sixth Biennial Review” published in 2016 by National Academies of Sciences, Engineering, and Medicine,” the area south of the Tamiami Trail was historically wetter than it is today. The construction of the road from Tampa to Miami created a coast-to-coast berm which disturbed the natural freshwater sheetflow. When the Tamiami Trail was originally constructed, it often flooded and it was customary to close the road during the wet season. However, after the road was built up to accommodate heavier traffic, water levels were artificially regulated to protect the roadbed. As a result, the area south of the trail began to dry out, and the muck oxidized, changing from wetlands to marl prairie. Efforts to protect the road also meant water backed up north of the trail and limited how much water could be sent south from Lake Okeechobee.
As part of CERP, portions of the Tamiami Trail have been raised and old roadbed removed to allow more water to flow under the road. However, to protect the nesting area for sub-population A, the U.S, Army Corps of Engineers shuts the S-12 A and B water control structures nine months of the year, restricting freshwater flow in that area.
Even with current protections in place, the sparrow populations are declining, the U.S. Geological Survey report states. “A steep decline in bird count for subpopulation A was observed over the last 30 years, down to an estimated 0 birds observed in the range-wide point count surveys in 2021. The number of birds in subpopulations C, D, and F is relatively low and has declined since 1981 (although subpopulation D has shown a recent increase), while subpopulations B and E have relatively stable and higher number of birds. Subpopulation estimates for 2021 are: A, 0; B, 1,488; C, 112; D, 288; E, 528; and F, 32.”
According to USGS: “Organizations such as the National Park Service can use this new USGS research to understand how the sparrow is likely to respond to sea level rise and then decide if management actions should be adjusted to meet desired future environmental conditions. This study can inform decisions that balance protecting the many endangered and endemic species in the Everglades, other aspects of the environment and the needs of the local community.”