ISLE OF PALMS — Every spring for at least three decades, tiny darting birds have arrived at the old Red & White grocery like hordes of shoppers to stake out their spots.

Least tern nests

State wildlife biologists are tracking roof-top nesting by least terns. People who think they have spotted a nest are asked to email or call (843) 509-4845.

The least terns made a mess of the grocery’s glass awning, but the owner let them be. All they wanted was the flat, pebbly tar roof — to nest.

Lives on the Sea

This is part of an occasional series looking at how the coast and the ocean are changing and what it means for a region where people have made a life and a living for generations in tune with the sea.

When the now-closed grocery is razed, the roof will go with it, another vital bit of breeding ground improvised by a spectacular shorebird the state considers a threatened species. The roofs, too, are on their way out: Building codes no longer allow them.

Least tern facts

They are the smallest North American tern, with a wingspan twice the length of its 9-inch body.

They winter along the northern coast of South America and the Pacific coast of Mexico.

They nest in colonies.

They hunt for small fish by hovering over the water and dropping to plunge.

Cornell Lab of Ornithology, S.C. Department of Natural Resources

It could be the second shoe to drop for the terns, which were nearly wiped out in the early 20th century for hat feathers.

In recent years, least terns have been losing their once-isolated pebble beach rookeries to human intrusion.

But a S.C. Natural Resources technician is trying to find them a future — in box frames the size of a small TV screen, lined with sand and gravel, set on rooftops.

“We’re trying to create as natural a nesting place as possible,” said Mary-Catherine Martin of DNR.

Six skeletons

The least tern is the whirling dervish of the coast, a sparrow-sized bird that looks like a skinny gull and is incredibly agile on the fly. A wooing male will dart, dance and hover in the air with a fish in its mouth, then feed it to the female.

The birds’ roof nesting first was noticed in the 1980s. The terns apparently like loose gravel roofs because they resemble the pebble rookeries where they scoop pebbles into a small pile for a nest. The sites are relatively safe from predators such as raccoons.

The terns turned to summer nesting on roofs as the rookeries were lost to beachcombers and their dogs. Least terns are flighty, to say the least: They scatter at disturbances. Today, there are really only two natural nesting sites left in the state, on Cape Romain and at Botany Bay, and both repeatedly fail to produce offspring.

The roofs aren’t much better: They are too hot, the young chicks get stuck in melted tar and occasionally get washed off the edge by rainwater. Martin found six skeletons caught in the tar around a single vent, where the terns evidently grouped for the shade. But for now, the roofs are home; 85 percent of the nests in the state are on roofs. In its peak year, the Red & White roof alone held 85 nests.

“It’s not the most hospitable environment, so if we can make it better, we will,” Martin said.

‘In their path’

The sturdy, soft-spoken Martin isn’t a biologist. She’s a former occupational therapist who works for DNR primarily as a fisheries technician. The least tern work for her is extra, volunteer duty. She just loves birds — enough that she’s the handler of an African spotted eagle owl.

“I love their behavior. I love how they look. Everything about birds is amazing to me,” she said.

She and others had been puzzling over how to provide more rooftop nesting opportunities for the terns when she came across Green Roof Outfitters’ plant-growing “modules,” which she could convert into nesting boxes. She approached the Beach Co. about building a nursery of the modules on the pebble-less roof of the supermarket that will replace the grocery.

Leonard Way, Beach property management vice president, is dubious but interested. He offered a nearby roof as a sort of test lab, to see if the modules will work.

“If this (roof) is in their path, and they like to come up here, let’s try it out,” Way said. “So long as it isn’t damaging in any way to the structure, why not make use of the space?”

Michael Whitfield of Green Roof donated 19 modules.

Now it’s up to the terns, which are expected to start arriving in the next few weeks.

‘A little more tolerant’

If the boxes work, they could be offered to other flat roof owners who want to provide habitat; they could become one of those 21st century wildlife-management solutions where humans find a way to coexist with a species rather than drive it out.

But it’s far from a done deal. Martin also has set small open piles of sand and gravel for nests around the perimeter of the boxes, just in case the wary terns don’t use them.

If the birds do, there’s still the other, sometimes not-so-tolerable side effect to reckon with: The birds can make a mess.

“I think if people maybe realize they’re just nesting up there, and they’re doing it because they don’t have a place out there anymore, people would be a little more tolerant,” Martin said.