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Northern Leopard Frog

(Rana pipiens) Special Concern

Identification: Upper side green or brown, with large rounded or oval spots; skin smooth; eardrum usually lacks distinct light spot; ridge of each side of back, read end of ridges not distinctly curving toward middle; hind toes with extensive webbing; rear of thigh with dark spotting; head and body length up to about 11 cm (4.3 inches).  

Mature male: base of innermost toe on front feet swollen during breeding season; expanded vocal sacs, one on each side, extend above front legs.

Breeding call : A prolonged snore lasting 2–3 seconds followed by 2–3 series of stuttering croaks or chuckles (sometimes the chuckles are given without the introductory snore and vice versa).      

Larvae: Upper side dark brown or olive to gray; snout pointed when viewed from above; mouth at tip of snout; eyes high on head; iris gold, surrounded by dark spots; intestinal coil often visible through skin; tail fin moderately high, 65–80 percent of body length, with sparse pigment; usually 2 (rarely 3) rows of tiny teeth on upper lip, 3 rows on lower lip; large larvae average about 6 cm (2.4 inches) long, up to at least 10 cm (3.9 inches) long; larvae near metamorphosis with oblong dorsal spots, rear surface of thighs with mottled dark bars.

Eggs: Deposited in large, somewhat flattened globular masses 5–15 cm in maximum diameter and including up to several thousand eggs; usually attached to vegetation in shallow water.

Colorado Distribution: Nearly statewide in mountains and lowlands, but scarce or absent in most of southeastern Colorado and the Republican River drainage in northeastern Colorado. Locally common, but now rare or extirpated in many areas, particularly in the mountains.      

Habitat: Wet meadows and the banks and shallows of marshes, ponds, lakes, reservoirs, streams, and irrigation ditches. May roam far from water during wet, mild weather.

Life History: Breeds in shallow, quiet areas of permanent bodies of water, in beaver ponds, and in seasonally flooded areas adjacent to or contiguous with permanent pools or streams. The breeding season begins in March in lowland areas and occurs mainly in May and June in the mountains. Larvae metamorphose into small frogs as early as late June in the lowlands and mainly July-September in the mountains.    

Note: This species hybridizes with the plains leopard frog in some areas, so some frogs have mixed identification characteristics.