Amphibians have been referred to as the “canary in the coal mine” because they are so susceptible to environmental pollutants. As animals that breathe through their moist skin as well as with their lungs (or gills in the tadpole stage), they become exposed internally to anything that can enter through the pores in their skin. Here at St. Olaf we have been very pleased with the large amphibian populations that have developed as a result of our wetlands restoration projects. We have documented 9 species of frogs, toads and salamanders in our wetlands. This is an indication of the low pollution levels in our restored wetlands, undoubtedly due in part to the large amounts native vegetation (prairie &/or woodland) planted around these wetlands. Chorusing of many species can be heard on campus starting with the Western Chorus Frog in late March to the Gray Tree Frog that is still chorusing into August.
American toad (Bufo americanis)
Call Description: A long, drawn-out, high-pitched, musical trill lasting up to 30 seconds. The male’s vocal sac is round when inflated.
Physical Characteristics: American toads are brown or reddish with dark blotches and warts on their backs.They have whites chests with dark speckles. These toads range between 2-3.5 inches in length.
Cope’s gray treefrog (Hyla chrysoscelis)
Call Description: A fast, metallic buzz like trill.
Physical Characteristics: This frog can change colors, so it can be anything from a mottled grayish green or solid green to a gray or creamy white color. The inner thighs on the hind legs of all gray tree frogs are yellow. The cope’s gray treefrog ranges between 1.25-2 inches.
Gray treefrog (Hyla versicolor)
Call Description: A musical, birdlike trill. The call is similar to the Cope’s gray treefrog, but slower. They may call while perched in tree branches.
Physical Characteristics: Looks identical to the cope’s gray tree frog. These two species can only be distinguished by differences in their calls. A cope’s gray tree frog has a higher, shriller call than the gray tree frog.
Spring peeper (Pseudacris crucifer)
Call Description: Short, loud, high-pitched peep. Many individuals together sound like sleigh bells.
Physical Characteristics: The spring peeper is tan with a dark “x” on its back. This frog is very small ranging between 0.75-1.25 inches.
Western chorus frog (Pseudacris triseriata)
Call Description: The call of the western chorus frog is a rising creeee that sounds like a fingernail being dragged across a comb.
Physical Characteristics: The western chorus frog has a color that is tan, gray, or red with three dark stripes extending from its head down its back. Another line crosses across the frog’s eye and a white line runs across the upper lip. This is one of the smallest frogs in Minnesota ranging between 0.75-1.5 inches.
True frogs (Ranidae)
Bullfrog (Rana catesbeiana)
Call Description: A series of deep brass notes sounding like rrr-uum or jug-o-rum.
Physical Characteristics: This is the largest frog in North America, ranging from 3.5-8 inches in length. Bullfrogs are have green skin with yellow skin on the throat of males and white skin on the throat of females.
Northern leopard frog (Rana pipiens)
Call Description: A deep snore lasting several seconds and ending with a chucking.
Physical Characteristics: The color of this frog ranges from green to brown with irregularly spaced, dark spots on its back and legs. This frog ranges from 2-3.5 inches in length.
Wood frog (Rana sylvatica)
Call Description: A short chuckle that sounds like a harsh racket, racket, racket. A chorus sounds like the feeding call of a mallard.
Physical Characteristics: Wood frogs range between brown, reddish-brown, and almost black with a dark patch around their eyes and two big ridges. They grow to be between 2-2.75 inches in length.
Tiger salamander (Ambystoma tigrinum)
Physical description: The tiger salamander is black with yellow markings. These salamanders look very similar to spotted salamanders, but are more common.