Rio Grande Leopard Frogs (Lithobates berlandieri) will usually call while floating in shallow water. Their vocal sacs protrude laterally from the sides of their heads. This individual was calling from a flooded riparian area underneath a bridge in McMullen County, Texas.
The higher pitched clicking heard behind the Leopard Frogs are the calls of Blanchard's Cricket Frog Acris blanchardi
This spectrogram represents the first three "croaks" of the preceding call.
2016 Addendum -
Like most frog species the sound of the call of the Rio Grande Leopard Frog can change with ambient temperature. At lower temperatures, the tempo of the snoring call slows down and sounds a bit different. You can hear that by comparing these calls from one of my favorite roadside ponds near Quihi, Texas.
One summer evening in August I stopped by there to record some Rio Grande Leopard Frogs along with other species. Here's what they sounded like in this warm shallow pond at an air temperature of 75°F (and a water temperature probably a bit higher than that) -
I returned to this pond on a cool winter evening (for south TX that is) after it had rained heavily and was 56°F. The only species calling that night was the Rio Grande Leopard Frog.
Notice how much less "snore-like" it sounds.
© Chris Harrison 2012 & 2017