Rising sea levels are threatening rare saltmarsh sparrows

Sparrows are facing threats from habitat loss even in cities that several species of them call home around the world. Yet many of the energetic little birds will be having it rough in coming decades for another reason: climate change.

Take seaside sparrows (Ammospiza maritima) and saltmarsh sparrows (Ammospiza caudacuta). The two closely related species almost exclusively inhabit coastal salt marshes where their nests are set to be destroyed by increased flooding brought on by rising sea levels in coming decades.

Already saltmarsh sparrows are experiencing an annual drop of 9% in their numbers in coastal New Jersey in the United States, according to a new study.

A team of researchers has set out to estimate the projected population levels of seaside and saltmarsh sparrows in the coastal areas of the U.S. state. Seaside sparrows will be faring fairly well in the face of climate change because, the scientists postulate, members of this species can likely withstand a rise of between 0.35m and 0.75m in sea levels.

Not so saltmarsh sparrows, however. Even a relatively small rise in sea level can send their populations plummeting. The results indicate that they could go extinct by the middle of the century. “We found that the Seaside Sparrow population persisted under both sea-level rise scenarios; however, the Saltmarsh Sparrow population reached a quasi-extinction threshold within 20 yr,” they write.

“Using the same framework, we modeled potential management scenarios that could increase the persistence probability of Saltmarsh Sparrows and found that fecundity and juvenile survival rates will require at least a 15% concurrent increase for the local population to persist beyond 2050,” they elucidate.

Worldwide, salt marshes comprise around 45,000 square km with a third of that spread along the coasts of North America. Of the 25 species or subspecies that are restricted in their habitats to tidal wetlands worldwide, 15 live in the U.S.’s Atlantic and Gulf coasts. “Given rapid climate changes and other threats to salt marsh ecosystems, many of these species are in serious danger,” the scientists note.

“The global breeding range of the saltmarsh sparrow extends from Virginia to Maine, with a population estimate of 60,000 birds. Sea-level rise can negatively impact breeding seaside and saltmarsh sparrows by reducing the amount of available habitat, and by increasing nest flooding rates,” they explain.

“Furthermore,” they add, “the high human population densities of Mid-Atlantic states also make it difficult for sparrows to thrive in the region.”