The Frog We Didn't Know Was There
Last Friday night as most of the 68 frog walk attendees headed for the parking lot at the John Heinz National Wildlife Refuge, I paused with a few stragglers and a couple of the refuge staff to listen to some rubbery-sounding chuckles coming from the marshy edge of the Impoundment (the large shallow lagoon bounded by an embankment). Now and then one of the frogs worked in a little bit of a snore sound. I felt a short burst of delight and triumph to hear the Atlantic coast leopard frogs (Lithobates kauffeldi) calling in the dark, even if the staff leading the walk and I wanted to yell at the frogs for not having made any noise half an hour earlier when we had initially stopped at that spot with the full group of attendees. At that earlier point all we heard were the spring peepers, high-pitched and impressively loud for a finger-nail-sized creature.
Now, a truth of nature-walk-leading is that the vast majority of the attendees will be pleased with plants and animals that the leaders have seen a million times and consider nothing-to-write-home-about, but those leopard frogs are pretty special.
I had heard them at the refuge more than 12 years ago when I took part in frog listening surveys with the then-refuge director and an elder birder named Skip Conant.* At the time we marked them down as wood frogs, known for calling in early spring with a call that sounds kind of like ducks. Had anyone seen a wood frog at the refuge lately? Nope. And while lots of frogs are cryptic (the whole point of a frog call survey is to detect them by their singing, which is hard to miss), wood frogs have a habit of turning up on land when they’re around. You’d notice them hopping out of your way now and then.
Not long after those frog call surveys a herper from Delaware County, Dave Fitzpatrick, reported seeing leopard frogs at the refuge. Everyone figured they were southern leopard frogs (Lithobates sphenocephalus), a species often seen across the river in southern New Jersey. They were wrong.
Scientists only realized these frogs are a distinct species a little more than a decade ago, with the paper describing them coming out in 2014. And they weren’t discovered in some pristine sanctuary. They were encountered in the vast, polluted, invasives-overrun freshwater tidal marshes around New York City. These are frogs Mid-Atlantic urbanites can call our own.
It then made perfect sense that the wood frogs we had been hearing but not seeing, and the leopard frogs we had been seeing, were the same frogs.
Even today these frogs are pretty special. On top of getting by in substandard marshes, they have a small range, and in Pennsylvania are found pretty much only in marshes in our corner of the state. The easiest place to observe them is the wildlife refuge. Listen for calls that sound midway between ducks quacking and rubbing a balloon. There aren’t very many evening frog walks left for their breeding season, but on a cloudy day in April you still have a shot at hearing them call.
*I didn’t know him as a birder, but as a herper I grew up with his father Roger Conant’s guide to the Reptiles and Amphibians of Eastern and Central North America as my bible. Roger Conant would have been a giant in North American herpetology simply for authoring that guidebook, but he also ran the Philadelphia Zoo and founded the Philadelphia Herpetological Society (now defunct). And there I was rubbing elbows with someone who was 50% Roger Conant, biologically-speaking, at least.