Amid a daily percussion of artillery fire and munitions explosions, a rare amphibian migration began at Fort Bragg in early March.
Carolina gopher frogs emerged from their underground burrows and hopped a mile or so to seasonal ponds. Their instinct to breed was sparked by several days of rainfall and warm nights.
About 100 to 150 Carolina gopher frogs live in Fort Bragg's artillery impact zones, where soldiers train. North Carolina lists the frogs as "threatened."
N.C. State University biologist Nick Haddad studies the frogs, which live in intact sandhill and longleaf pine ecosystems that require periodic burning. With the widespread loss of this habitat - only 5 percent remains compared with its historic range - the frogs have developed a curious dependency upon military lands such as Fort Bragg.
Haddad receives funding from the Department of Defense to monitor Fort Bragg's amphibians, and he has yet to document a single juvenile gopher frog exiting the breeding ponds. The waters dry up too soon, leaving tadpoles stranded. Or there's not enough rain and warmth at the right time, so the adult frogs don't bother to show up at the breeding sites, he said.
"The gopher frog population on Fort Bragg must be declining," Haddad said. "In the seven years we've been studying them here, this is only the second time we've seen them turn out in any great number to breed. But we've also had a few years of extended drought, so it's difficult to do these surveys and feel confident that things not being there really means they are not there."
He hopes this year will be different. Gopher frogs began showing up in his live traps, set around their breeding sites, during the second week of March.
"You pretty much only see them when they emerge to breed," said Will Fields, one of Haddad's graduate students. Fields drives from Raleigh to check the traps each time rain is forecast during the gopher frogs' breeding window.
While soldiers trained with small arms weapons and exploded munitions nearby, the 2- to 2.5-ounce males and 2.5- to 3.2-ounce egg-carrying females made their way across the forest floor. Some arrived with fresh dirt streaks atop their heads, an indication of just how recently they had emerged.
After surveying dozens of seasonal ponds across the base, Haddad and Fields found three that the frogs used for breeding. They encircled the ponds with a black plastic "drift fence" 18 inches high and dug into the ground. Five-gallon buckets were sunk in the ground every 20 to 30 feet along the fence. Holes allow groundwater in. Amphibians trying to reach the pond are forced by the fence into the bucket traps.
On each visit, Fields checks every bucket - one on each side of the fence, to catch frogs moving toward the pond and departing - to document the contents and then release them.
The morning of March 12, he logged several amphibians, including nine of the elusive Carolina gopher frogs. Two were females bloated with eggs.
Fields and Haddad implant tiny tags the size of rice grains in the gopher frogs, similar to ID chips placed in household pets. When Fields scanned the gopher frogs that morning, three of the seven males were already tagged. Using a syringe, he painstakingly implanted new chips in the other two males. He'll tag the females after they've spawned.
Fields' doctoral work includes documenting the number and sex of gopher frogs coming and going from Fort Bragg's breeding ponds. He and Haddad plan to model the population's status - if it's declining or holding stable - and track details such as how long the animals live and how often they breed. Such details could help researchers restore the population or afford the species stronger protections if necessary.
"Fort Bragg is being really forward-thinking in this research," Fields said, noting the base is not compelled to monitor amphibians.
Haddad has studied how to breed the frogs in captivity, in order to release them and augment wild populations. He has permission from the state to pluck eggs from their breeding sites, and survival rates among the captive-bred frogs are as high as 90 to 100 percent, he said.
The challenge is where to put them. "Large tracts of land are this frog's hope," said Alvin Braswell, a herpetologist at the N.C. Museum of Natural Sciences in Raleigh. "But the key to reintroducing it anywhere is taking care of the reason it declined in the first place. Otherwise, you're just spinning your wheels."
Unfortunately, there aren't many true seasonal pools left in North Carolina. Fort Bragg's gopher frogs breed in "borrow pits," shallow depressions near roads where the military removed dirt for other uses. Braswell said historically the frogs bred in Carolina bays, naturally formed elliptical depressions unique to the Carolina coastal plains. But 95 percent of these bays have been lost or altered due to ditching and draining, he said.
The frogs need more than the lowland ponds. Their burrows are in upland forest habitat, but no one is entirely sure how much land they use. To see where they go after breeding, Haddad has tracked them by dabbing fluorescent dye on their bodies. When they move, they leave a dye trail that shows under black light. His students trailed adult gopher frogs "the length of two football fields" away from breeding ponds. Braswell said they likely need about a mile radius of forest or sandhills around each pond.
Though no one knows how many Carolina gopher frogs live in the state, Braswell's records show 23 known breeding sites, including Fort Bragg's, all crammed into the Southern coastal plain. Gopher frogs were recorded as far north as Beaufort County in the 1930s, but today Fort Bragg, Croatan National Forest, Camp Lejeune and state game lands represent the extent of its last habitat holdouts in North Carolina.
"It's happenstance that we've inadvertently created these protected areas on military installations for many rare species," Braswell said. "The few good sites we have left should be cherished and managed diligently."
Connecting isolated populations is a problem, too, said Brian Ball, a civilian biologist who works in Fort Bragg's Endangered Species Branch and collaborates with Haddad and Fields.
"If you don't have ponds that connect, then you will get populations that are isolated from each other," Ball said. "And then they'll blink out."
But there is a slim ray of hope. Climatic conditions were "set up just right" this spring for the frogs, Braswell said.
Even so, Haddad said he plans to identify potential restoration sites on public lands this summer.
T. DeLene Beeland: firstname.lastname@example.org