Bullfrog (Rana catesbeiana) 



Description: The largest of North American frogs, adult Bullfrogs may reach 8 inches in snout- 

 vent length. The skin is smooth. Adults are usually pale to dark green or brownish green 

 with darker spots or blotches. There are a series of black bands across the legs. The 

 underside is cream to yellowish with gray mottling. No dorso-lateral folds are present, 

 however there is a prominent ridge running from the eye over the tympanum to the shoulder. 

 Males have extensive yellow pigment on the underside, especially in the throat region, and 

 swollen thumbs. The diameter of the tympanum is larger than the diameter of the eye in 

 males but about the same size in females. Egg masses consist of thousands of eggs and may 

 reach several feet across. Tadpoles may reach 1 1 .3 cm in total length and are olive green 

 with numerous black spots dorsally. The belly is white to creamy with varying amounts of 

 dark mottling. Tadpoles usually take two or more years to metamorphose. 



Habitat and Habits: Bullfrogs are the most aquatic of Montana's amphibians, rarely being seen 

 far from the water's edge and usually in the water. They are associated with larger bodies of 

 quiet water such as ponds, lakes or backwaters of streams, usually with extensive emergent 

 vegetation such as cattails or reeds. They emerge in the spring only after air and water 

 temperatures have warmed considerably and insect populations are beginning to proliferate. 

 Breeding probably takes place in July in western Montana when males attract females to their 

 territory by a series of loud brr-umps. Adults were seen in 1995 near Darby in June, and 

 heard 10 July near Corvallis, and 12 July at Lee Metcalf National Wildlife Refuge; silent 

 adults were seen near the Bitterroot River at Florence on 14 August. Tadpoles were seen at 

 the Florence site on 22 April (R. Torquemada pers. comm.), and have been found in ponds 

 near Lolo (B. Hossack pers. comm.). Bullfrogs appear to be expanding their range in the 

 Bitterroot Valley. The large mass of eggs tend to float on the surface when first laid, but sink 

 into the water prior to hatching (Hammerson 1982a, Nussbaum et al. 1983). Tadpoles over- 

 winter in the Pacific Northwest, transforming during their second summer (Nussbaum et al. 

 1983, Leonard et al. 1993). The bullfrog is a voracious feeder, eating anything smaller than 

 itself, including ducklings, fish, mice, frogs, and small turtles. Bullfrogs have been 

 implicated in extirpations of native frogs and turtles, and declines in waterfowl production 

 (Hammerson 1982b, Leonard et al. 1993). Native amphibians and hatchling turtles are rarely 

 seen where once they were common at Lee Metcalf National Wildlife Refuge (P. Gonzales 

 pers. comm.), while Bullfrogs are now abundant. 



Surveying: Both tadpoles and adults can be sampled by using a dipnet. Capture success of adults 

 is enhanced by night sampling using a headlamp, as they are very wary and do not allow 

 close approach during the day. 



Status: Bullfrogs are native to the eastern and central U.S. and exotic in western states. They 

 were introduced into western Montana prior to the 1 960's. In the BNF area, the species was 

 fu-st reported in 1966, although Black (1969) stated the species was introduced into the 

 Bitterroot Valley about 1920. The Bullfrog appears to be restricted to the Bitterroot Valley 

 along the Bitterroot River in Ravalli and southern Missoula counties (Appendix 3). There are 

 no records from BNF lands, but the species may expand its range onto the Forest at lower 

 elevations in the Bitterroot Valley. 



Montana Natural Heritage Program rank: G5 SE3. 



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