Wood Frog

Lithobates sylvaticus (Rana sylvatica)

Wood Frog

Distribution in Wyoming

 

 

 

 

 

 

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The Wood Frog is the most northerly distributed amphibian species in North America. Its range includes most of Alaska and a wide swath cutting through Canada into the New England states and then south into Georgia and Tennessee. In Wyoming it is a relict species, left behind when Pleistocene glaciers retreated north about 10,000 years ago. The distribution is comprised of two disjunct or island populations: one in the Snowy Range and another in the Big Horn Mountains. It is found in the montane and subalpine life zones between 8,000 and 10,000 feet where it inhabits ephemeral pools, beaver ponds, and small lakes.

Wood Frog Wood Frog

It is a medium sized frog about 2 inches long (SVL) with fairly short hind legs and a pointed snout. It is distinguished from the Spotted Frog (with whom it enjoys a sympatric overlap in the Big Horn Mountains) by having smoother skin, a more distinct black face mask and white stripe along the lower jaw, and by lacking the salmon pigmentation on the legs and feet. Individuals from the Snowy Range have a well-defined mid dorsal stripe, but this stripe is weak or missing on specimens from the Big Horn Mountains.

And now for the frog’s specialty: brown! The dorsolateral fold appears as though it was squeezed out of a tube like a ribbon of auburn honey and is edged along its upper margin with a smear of almond meringue. The exquisite chocolate of the dorsal surface suggests a light dusting of cinnamon and the larger, flecked shavings of coffee bean. The rich carameling of the back seems to ooze down, smothering the legs and thinning to a delicate basting along the sides.

Wood Frog Wood Frog

Breeding activity starts early, when ice-free areas are just forming in the sunlit shallows along northern shores. Males voice the soft quack of a little duck to advertise their availability. Mating pairs may remain in amplexus from 2 hours to 2 days—the extended period of time being required to further ready the female’s reproductive condition and allow the ova a bit more time to mature. The resulting spawn are fist sized masses floating just beneath the surface and containing 500 to 1,500 fertilized eggs. With temperatures still cold enough to form panes of ice each night, it takes 4-7 days before the developing embryos hatch from their jelly cases. Metamorphosis requires another 10-12 weeks; but many of the ponds, having a different agenda, dry up before tadpoles have completed their to-do list. For those surviving, sexual maturity is reached 2-3 years later.

Wood Frog Wood Frog