About Mink Frog and American Bullfrog

Mink Frog – Rana septentrionalis

Mink Frogs occur farther north than many other large frog species.  The name comes from the characteristic mink-like color emitted by the adults when they are handled.

Appearance: The dorsal color pattern of the Mink Frog is a green background with variable dark mottling.  There is a fold on each side of the back, prominent toward the head and becoming less visible toward the posterior.  The hind legs have irregular dark blotches.

Character for these species : They are usually more darkly mottled than Green Frogs or American Bullfrogs, but this is not a reliable character for distinguishing these species.

Female Mink Frog : In females, the eardrum is approximately the same size as the eye, while in males the eardrum is larger than the eye.  Tadpoles grow up to 3 inches long and have a pinkish wash, dorsal mottling, and an opaque white belly.

American Bullfrogs : They have no folds on the back.  In Green Frogs  legs are cross banded, whereas in Mink Frogs they are blotched.  Tadpoles of Mink Frogs are difficult to distinguish from Green Frog tadpoles.

Mink Frog – Rana septentrionalis

Habitat and Behavior: They  occupy permanent water and prefer ponds or lakes with lily pads.  Newly transformed juveniles travel overland in search of new aquatic habitat.  Once established in suitable habitat, adults seldom venture far from water, spending the winter at the bottom of their home pond.  When they feel threatened, They escape by entering the water.  They usually “skip” across the surface before diving, while Green Frogs dive immediately.

Reproduction: Frogs breed from early summer to mid-August in permanent water.  Males produce a repetitive knocking call.This species spends one winter as a tadpole before transforming.

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American Bullfrog – Rana catesbeiana

Ontario’s largest frog species is found only in permanent water, where it’s calls are a familiar sound of summer.

Appearance: The back is medium green, with a pattern varying from only a few dark spots to extensive dark mottling.  The underside is white with occasional mottling.  The throat is often tinged with bright yellow and may be  yellow in males.

In males the eardrum is larger than the eye; in females it is about the same diameter as the eye.  Tadpoles grow up to 4 inches, white opaque belly, and covered with small black dots.

Mottled American Bullfrogs : They confused with Green Frogs or Mink Frogs, but American Bullfrogs have no folds along the sides of the back.  These folds are present in the other two species.

American Bullfrog – Rana catesbeiana
American Bullfrog – Rana catesbeiana

Habitat and Behavior: Adults seldom move far from permanent water, but young frogs travel in search of new habitat, often overland. Spend time underwater in winter.  American Bullfrogs consume insects, other aquatic invertebrates, and other frogs.

Reproduction: They usually breed in June, later than most other amphibian species.  The breeding period is over several weeks.  Unlike those species that breed in early spring in shallow or temporary pools, bullfrogs prefer deeper, permanent water.

Environment setup : Males set up environment in suitable breeding places and advertise by emitting a distinctive two or three note bass call.  Females can produce up to 8000 eggs, which form a floating mat at the water surface.

The eggs hatch after a couple of days, and the larvae spend one or two winters as tadpoles before transforming.



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