56: Northern Leopard Frog and Plains Leopard Frog
I write to you from Arapahoe, Ute, and Cheyenne land. I am interested in learning about the different animals that live in the place where I was born. Before we start with today’s animal, I want to emphasize that biological classification as understood by western society has its roots in racism, sexism, and transphobia – here’s a good explainer about why.
Today’s animal are two species of frog: the Northern Leopard Frog (Rana pipiens) and the Plains Leopard Frog (Lithobates blairi), both named for their distinctive dark-spotted backs. The Plains variety is common in its range which, as you may have guessed, is across the Great Plains. They breed in open water, but adults can range far away from it. They can be found in the canyon country of southeastern Colorado, such as along the Purgatoire or the Arkansas, some of the only places where there is open water in this arid portion of the state.
The Northern Leopard Frog historically occupied almost the entire state, ranging from elevations of 3000 to 12000 feet above sea level. However, their population has seen a precipitous decline, leading to them being classified as a species in need of conservation by Colorado Parks and Wildlife. The reason for this is probably the spread of the invasive American Bullfrog species, who are larger and will eat the Leopard Frogs. The Leopard Frogs’ native predators include the Pied-billed Grebe, Great Blue Heron, Burrowing Owl, Northern Watersnake, Western Terrestrial Gartersnake, and Western Tiger Salamander. Game fish are also predators of all life stages of the Northern Leopard Frog.
You can hear a nice example of their call with a Boreal Chorus Frog (#21) about halfway down the page here.
All leopard frogs come in either two colors: brown or green. This is determined by a gene that has two forms (alleles). Why a particular frog is one of these colors, however, does not correspond to anything geographically related so does not seem to be related to camouflage. This article describes a PhD project which found that color corresponded to developmental rate. Basically frogs who live in an area with more pressure from predators reach adulthood more quickly as an evolutionary strategy. These frogs are more likely to be brown. Meanwhile in places where there are fewer predators, there are more green frogs, who tend to take a long time to become adults but whose eggs are larger and more abundant.