Northern Leopard Frog (Rana pipiens)

Description: The leopard frog is a slender, medium-sized frog; females range from 5.4 to 9.5 cm (2.1-3.7") snout-vent length, and males range from 5.2 to 8.2 cm (2-3.2"). Only one other species of frog in Maine, the pickerel frog, has distinct spots. The leopard frog has 2 to 3 unevenly spaced rows of irregular oval-shaped dark spots that pattern the dorsum. The pickerel frog, in contrast, has 2 parallel rows of evenly spaced, squarish spots and is colored a bright yellow-orange on the under surfaces of the hind legs. Leopard frog spots have light borders on a background of green and/or brown shades. There are 2 spots, one over each eye. When inactive, elongated spots on the legs form 1 to 4 bands (Gilhen 1984).The undersides of the frog are white to grayish white and are unmottled. The frog is also able to darken itself when its surroundings are dark (Fernandez and Bagnara 1991). Two possible benefits to this adaptive coloration are that the animal is less likely to be seen by a predator, and that the ability to absorb the sun's energy increases (dark objects absorb heat better than lighter objects) thus helping the animal to warm up. The white undersides are thought to mimic or resemble the reflective surface of the water. This is especially important if a frog is to go swimming safely and not be detected by a hungry fish looking upward for a meal! Occasionally, northern leopard frogs without spots on their backs are reported (Merrell 1965, 1970), but none has been reported in Maine.

Blue leopard frogs have been documented in Maine, as have blue bullfrogs and green frogs (Berns and Uhler 1966).The blue color occurs when the skin lacks the surface pigment that would normally absorb blue light (see Black 1967 for summary).Without the pigment, blue light is reflected, and we see a blue frog instead of a green frog.

During the breeding season, males can be distinguished from females by comparing the thumbs; males have enlarged or swollen digits to allow the male to securely clasp the female in amplexus. Two external vocal sacs are only visible when males are calling.

Tadpoles of the leopard frog have a combined body and tail length no greater than 8.4 cm (3.3").The pollywog is dark brown with fine gold spots dorsally with some aggregating on the sides. A bronze iridescence overlays a cream-colored ventral surface. The snout area may have an orange appearance, and the eyes are bronze. The tail, being a lighter color than the body, is marked with scattered fine spots and pencilings (Wright 1914).

Voice: Leopard frogs give 3 vocalizations: the advertisement call, the release call, and the warning cry. Associated with these vocalizations are various types of chuckles described as grunts, putts, clicks, burps, and quacks (Schimdt 1968).The advertisement call used to attract females is commonly described as a long drawn-out guttural snore lasting up to 3 seconds. The call is imitated as "ir-a-a-a------a-a-h" followed by several "rah-rah-rahs" if the male is pursuing a female (Noble and Aronson 1942).The advertisement call is given while the male is spread-eagled on the water surface, or sometimes underwater (Cook 1984).The release call is a short series of trills ("ir-a-a-ah---- ir-a-a-ah---- ir-a-a-ah----") used when males are clasped by other males or by females that are not gravid (Noble and Aronson 1942).The warning cry, an untrilled scream, is given with an open mouth when the frog is startled or captured by a predator.

Audio: Northern Leopard Frog call (coming soon)