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Mink Frog

Overview:

Scientific Name: Rana (Lithobates) septentrionalis

Size: 1.8 – 3” (adult size)

Status: Locally abundant in suitable areas.

Michigan State Status: Special Concern

MDNR Wildlife Action Plan Status: Species of Greatest Conservation Need

Habitat:

Inhabit cool, permanent waters with abundant emergent and floating vegetation. Favors slow streams, boggy lake inlets, natural impoundments, and spring-fed ponds where lily pads or other floating weedy vegetation is present.  

Conservation:

Listed as a species of special concern in Michigan, the greatest threat facing the Mink Frog is the transmission of amphibious diseases. Aeromonas is a bacterium that causes red-leg syndrome, which damages internal organs and leads to rapid death. Ranaviruses like frog erythrocytes virus (FEV) and frog virus 3 (FV3) have also decimated mink frogs at the local scale. Besides diseases, chemical contaminates have the ability to disrupt the progression of mink frog development and inhibit successful metamorphism.   

Best Management:

Identify and protect quality Mink frog habitat containing extant populations. Adhere to strict decontamination protocol regarding equipment and clothing when working in suitable mink frog habitat. Utilize vegetated buffer zones between areas of chemical application and aquatic systems as well as intercept chemical runoff before entering the system. Apply chemicals during late summer and early fall if necessary. Avoid mechanical aquatic weed harvesting and prevent introduction of invasive aquatic species. Avoid disturbing riparian and adjacent terrestrial area. If riparian harvest is necessary, maintain the understory and install erosion control measures. The management of beavers will also directly benefit mink frogs because the vegetative communities created by beaver impoundments in turn create ideal mink frog habitat. Provide egg laying structure by submerging finely brushed trees and ensure the presence of native aquatic plant communities. Create basking structures by partially or fully submerging logs and other objects.  

Adult Coloration:

The back and sides are green, olive, or brown and are pattered moderately to heavily with dark spots and blotches. The top of the hind legs has rounded spots lengthwise stripes. The upper lip is green. The belly is white often blending to light yellow on the sides and chin. Occasionally the underside is entirely yellow.  

Adult Characteristics:

The skin produces a musky odor when handled similar to rotting onions. Dorsolateral folds are poorly developed or absent but occasionally are present. In males, the tympanum (circular “ear” structures on the side of the head) is larger than the eye and the throat may be bright yellow. In females, the tympanum is smaller or equal to the eye and the throat is white or pale yellow. The call is a series or soft, low-pitched croaks “tok… tok, tok, tok, tok, tok” that is likened to distant hammering.  

Typical lifespan in wild: 1 – 4 years 

Breeding interval: multiple times annually 

Breeding season: June – August  

Range number of offspring: 500 – 4,0000

Average number of offspring: 2,000 

Range time to hatchling: 3 – 6 days (metamorphosis: 1 year) 

Average age at sexual/reproductive age (female): 1 – 3 years 

Average age at sexual/reproductive age (male): 1 – 2 years 

Diet: small fish, millipedes, insects, small frogs, leeches, snails, spiders; Tadpoles prey on algae though they have been observed consuming carrion.  

Predators: American Bullfrog, raccoon, Great Blue Herons, Wood Ducks, Spruce Grouse, Eastern Newts, Green Frogs, Eastern Tiger Salamanders, Eastern Garter Snakes, Five-spined Stickleback, Giant Water Bug, North American Leech 

Larvae Characteristics:

Tadpoles may reach 4” in length before they metamorphose. The back is green, olive, or brown with small dark spots or heavy mottling that can extend onto the tail. The tail is long with a pointed tip and fins may be edged with pinkish spots. The belly is yellowish and opaque.  

Species Confused With:

Young Bullfrogs can be similar but are usually green and have sparse spotting. Green Frogs often have heavy marking where their ranges overlap but the two can be distinguished by the Mink Frog’s odor and rounded spots or lengthwise bars on the hindlegs compared to the Green Frogs darker crossbands.

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