Mink Frog (Rana septentrionalis)

Description: The most distinguishing characteristic of the mink frog is its mink-like odor. Otherwise it can easily be confused with the green frog; the dorsum is an olive green and is spotted or mottled with dark, irregular-sized markings. Dark markings on the hind leg of the mink frog, however, tend to parallel the long axis of the legs rather than run across the legs as they do in the green frog. Furthermore, webbing on the toes of the hind feet extends to the last joint of the fourth toe and to the tip of the fifth toe in the mink frog, but rarely passes beyond the second joint of the fourth toe, and never reaches the tip of the fifth toe in the green frog. The ventral surface of the mink frog is grayish white, but pale yellow may appear on the lower sides and chin of some individuals. Dorso-lateral ridges may be absent, partially developed, or prominent, and are thus not useful for distinguishing this species from other Maine frogs.

Adult mink frogs range from 4.5 to 7.6 cm (1.8-3.0") long. Males usually reach sexual maturity less than 1 year after metamorphosis, when they are 4.5-5 cm (1.8-2.0") long, but females do not reach sexual maturity until they are 5.4-5.9 cm (2.1-2.3") long, which may be either 1 or 2 years after metamorphosis. If the snout-vent length is at least 10 times greater than the diameter of the tympanum, then the frog is a female; if the snout-vent length is less than 10 times greater than the tympanum diameter, then the frog is a male (Hedeen 1972a). Any frog less than 4.8 cm (1.9") long is considered a subadult and cannot be accurately sexed.

Mink frog larvae grow up to 10 cm (3.9") long. The dorsum is olive brown or greenish and is covered with small, dark spots. The belly is an opaque, straw yellow. The sides are mottled. The elongate tail has an acute tip, is paler than the dorsum, and is marked with irregular-sized dark blotches (Hedeen 1977).

Voice: Descriptions of the song of the mink frog provide a good example of how difficult it is to describe a complex sound in words. The mink frog's chant d'amour has been described as "a rapid squeaky croak"; rendered as "cut-cut, gh-r-r-r"; likened to "the sound produced by striking a long nail on the head with a hammer, driving it into heavy timber"; and compared to the song of a green frog, "but higher and slightly metallic." On the accompanying recording it is described as a series of taps sounding like 2 pieces of wood being tapped together.

Audio: Mink Frog call (coming soon)