New County Record: the Northern Leopard Frog (video)

Northern Leopard Frog at the Wetland, 3/31/2021

The handsome fellow pictured above is a northern leopard frog (Lithobates pipiens). I first heard these guys calling at the wetland on 3/25 this year. I knew they were leopard frog calls but there are multiple leopard frog species and I needed to review the calls and also wanted to check with some experts. I knew that what I was hearing were not the plains leopard frogs I've heard at the wetland in past years. There are different parts to the calls, but the most distinctive portion of the northern leopard frog call is a low prolonged snoring kind of sound. To my ears, it can also sound like the ominous creaking of a door being opened very slowly. You can hear this in the video below.

It has now been confirmed by others that these are northern leopard frogs. What makes that of special interest is the fact that this is the first documented occurrence of northern leopard frogs in Champaign County.  There are records of plains leopard frogs and southern leopard frogs, but northern leopard frogs have never been reported to the Illinois Natural History Survey (INHS) as occurring in the county. I myself did frog call monitoring at the wetland in 2019 and never heard northern leopard frogs, but this year in my visits over the past week and a half have heard them calling in numbers that could not have been missed. It seems that sometime within the past two years they have showed up at the wetland and successfully established a breeding population. How they got here is an interesting question which hopefully we may eventually find answers to.

For me, the best proof of their presence is hearing them call. They can be difficult to spot (sorry) because they seem to often call from underwater. The one above was more cooperative and sat still in hopes that I wouldn't find him, thus making it possible to get some decent photos.  Visual clues pointing to his identity as a northern leopard frog are the fact that the dark spots on his back are generally larger than his eyes and have a pale border around them and that there is a dark spot on top of his snout. In addition, the dorsolateral fold -- that raised fold of skin that runs from behind each eye to the rear of his body -- is continuous and unbroken in the groin area (although this is not visible in the photo above, it is visible in photos taken from other angles).

With regard to the video below, there were at least two or three northern leopard frogs calling in the vicinity of where the video is taken, though the camera is focused on only one... until another one bursts into the frame to chase the first away. It is not honestly clear to me that the one in frame when the video starts is actually calling.  Some of the still photos I have of that individual show sound waves moving out in concentric circles in the water around him, but that is not apparent in the video. Further, you will see when the second one bursts into the frame to chase the first one off, the second one has his vocal sacs inflated -- he is calling as he comes on scene.  Unlike the spring peepers and the boreal chorus frogs, which we've already seen, the leopard frogs do not have a single large inflatable throat vocal sac, but rather two vocal sacs, one on each side of the head at the corner of the jaws. You can see this as the "bully" comes on camera to chase the first one away.



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