If you wanted to find a new species of frog, the rainforest seems like a better place to look than the urban jungle. However, scientists have found a new species of frog living in and around New York City.

The new species, which biologists are calling the Atlantic Coast leopard frog, was hiding in plain sight. Besides its croak, the new species is nearly indistinguishable from several other frog species living in the area. As detailed today in PLoS ONE, the researchers were able to make the identification after comparing the DNA, appearance, and croaking noises of hundreds of frogs.

The authors, led by Jeremy Feinberg of Rutgers University, first announced their suspicions of the new species in 2012, when they reported that familiar-looking frogs with unfamiliar croaks were hopping around the wetlands near Yankee Stadium. Although the coloration of the Atlantic Coast leopard frog is very similar to that of other leopard frogs, its distinctive croak, which sounds like a simple, repeated "chuck," sets it apart.

Biologists have debated the number of leopard frog species for nearly 250 years, and other scientists weren't ready to declare a new species. Most dismissed the croak as a mutation in the known Northern or Southern leopard frog species. But now, Feinberg and colleagues say they have enough evidence, in DNA differences and acoustic analyses, to justify the new species designation. In order to declare that a frog's genome is different enough to declare a new species, the researchers found a significant collection of gene variants that were not found in any of the other species of leopard frogs. Frogs use sound to set themselves apart, so the researchers analyzed the waveform of the new species' croak to show that it had a different pitch, structure, and rhythm than other leopard frogs.

The Atlantic Coast leopard frog's (R. kauffeldi) range is centered on New York City. Feinberg, J.A. et al/PLoS One

The new species also fills different habitat niches than the other leopard frogs. For example, the Atlantic Coast leopard frog is much better suited for life in the coastal bogs of Staten Island than one of its sister species, which might favor New Jersey's Pine Barrens instead. This could help ecologists better plan their restoration efforts.

The Atlantic Coast leopard frog lives from northern New Jersey to southern Connecticut. Next time you're hiking in the area, keep your ears open for the sound in the video below.

The I-95 corridor is one of the most densely populated, and developed, regions in the world. Finding a new species in this type of environment shows that even the most well-trod places could be hiding fruitful ecological surprises. It just goes to show that New York City has surprises for everyone, even wildlife biologists.