For shorebirds, hurricanes aren’t the biggest threat

Shorebirds can weather destructive hurricanes, according to new research. A far bigger threat may be the gradual rise in sea levels.

“It’s tempting to focus on the big visible events when thinking about species extinction, especially for coastal birds,” said Christopher Field, a postdoctoral research fellow at the University of Maryland and the lead author of a study published recently in Ecology Letters. But, “it’s not surprising that coastal birds can deal with hurricanes, because they’ve evolved to deal with hurricanes.”

He and his co-authors had been studying coastal marsh birds for about a decade, including work on salt marsh sparrows (Ammospiza caudacuta) that showed their populations were declining. They had noticed that hurricanes didn’t seem to impact the populations they were studying much, but they wanted to gather more data to confirm what they were seeing.

Saltmarsh sparrow populations can withstand hurricanes. ©Mark Szantyr

The team conducted population modeling for salt marsh sparrows, willets (Tringa semipalmata), seaside sparrows (Ammodramus maritimus) and clapper rails (Rallus crepitans), projecting population numbers a couple of decades into the future. Then they looked even further into the future.

“We used these models to project the population forward [for 30 generations],” Field said, adding that the models also incorporated 10,000 iterations of random change and uncertainty.

They looked at a variety of situations, from hurricanes killing a few individuals to wiping out a population. It took a very large disturbance, they found, to create a situation in which the larger population of the species would take decades to recover.

“Even a big storm like Sandy didn’t seem to have much effect,” Field said, in part because the species have large populations. “The primary risk for these species isn’t going to be big storms.”

Rising sea levels pose a more “insidious threat,” Field said, because they threaten the narrow range of elevation and ecosystems that tidal marsh birds occupy, jeopardizing their ability to reproduce.

“It looks like sea level rise is going to cause a lot of problems for birds that require tidal marshes in some part of their life cycle,” Field said. Even modest increases in sea level projected by conservative climate models will result in the extirpation of local bird populations, he said.