Zoologist Brian Zarate first heard the creature's unfamiliar calls in 2003 while he and other researchers were working in the Great Swamp National Wildlife Refuge in Morris County.

The strange series of "chucks and occasional groans" emanated from a small frog no bigger than the length of a thumb.

One of them was captured and photographed by Zarate, then a state contract biologist with the Conserve Wildlife Foundation of New Jersey, who pondered the mystery along with his group.

It couldn't have been the southern leopard frog, a species found widely in the Pine Barrens, they reasoned. It must be a northern leopard frog released into the wild, possibly by a high school biology teacher.

At the time, the scientists didn't realize they were looking at a species that had not been described or mapped in any papers or field guides.

In October, it formally received its name: the Atlantic Coast leopard frog, Rana kauffeldi.

"It's kind of humbling, especially as a biologist, to realize that in a place like New Jersey, there's an opportunity to learn new things," said Zarate, who began working as a zoologist for the New Jersey Division of Fish and Wildlife's Endangered and Nongame Species Program in 2007. "This discovery teaches us not to give up on certain habitats that people might dismiss."

His first encounter with the frog in 2003 left many questions.

"There was nothing in the database we could reference," said Zarate, 37, of Bedminster Township, Somerset County.

He returned to the same area of the Great Swamp in 2007 and found the frog not only there but in other nearby wetlands.

Zarate videotaped the spotted creature and posted it on YouTube, where it was seen by Jeremy Feinberg, a doctoral student at the Rutgers University School of Environmental and Biological Sciences.

Feinberg had been tracking down other reports of an unfamiliar frog call on Staten Island, N.Y.

"Our role in the early stages was to help Feinberg's group and explore what was going on in New Jersey," Zarate said.

Feinberg's work followed claims by ecologist Carl Kauffield in 1937 that he had identified a new species of frog. Those claims were dismissed at the time.

Past researchers didn't have the technology such as DNA and digital bioacoustic analyses to provide evidence that the Atlantic Coast leopard frog was unique.

The proof came in a scientific paper in 2012 and was followed by more data in another paper authored by Feinberg, Zarate, and others in October. The new species was named after Kauffield.

"We presented it to the world and said why it was different," Zarate said. "It's different genetically, different in its calls, and different in the patterning on the legs."

Based on the state's database of frog records and information gleaned from professional experts, amateur frog aficionados, museum records, and the Internet, the frog has now been confirmed to exist in a wide range of habitats from Connecticut to North Carolina, virtually anywhere researchers went to confirm its call - the mating song of the male of the species.

"Any time a new species is discovered, it isn't that the animal is dropped on the earth," Zarate said. "Scientists just haven't formally described it or been to the area where that species exists.

"This frog has been in New Jersey a long, long time," he said. "People had been confusing it with other frogs."

The Endangered and Nongame Species Program is working on a two-year project to further refine the species' habitat range in New Jersey.

"New Jersey has been a leader in protecting valuable wetlands resources," said David Jenkins, the program's chief. "These efforts have included wetlands in urban and suburban areas that may not, on first blush, appear to be of great value to wildlife.

"This discovery of this frog literally in our backyard shows that New Jersey's swamps and marshes, even those in urban and suburban landscapes, still have tremendous value for our native wildlife and we shouldn't discount their value," Jenkins said.

Next spring, biologists and volunteers with the Endangered and Nongame Species Program will fan out to wetlands across the state, searching for more evidence of the Atlantic Coast leopard frog and collecting data on its habitat preferences.

"There's still a lot we don't know," Zarate said. "The Atlantic Coast leopard frog is a really interesting species that somehow manages to hang on even in urban environments."

"It's important we learn as much as we can about New Jersey's wildlife," he said, "and this discovery highlights the value in protecting our natural resources."