Bullfrog
Rana catesbeiana
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| Fig. 23. Bullfrog |
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Clearly, the bullfrog is Ohio's largest species of frog reaching a length of 100-175 mm. The aquatic bullfrog seldom ventures far from permanent ponds, lakes, or large streams or rivers. It emerges from hibernation and becomes active in early April but prefers warm weather and does not begin calling at breeding sites until mid to late May. The sonorous calls can be heard into mid-July, but the frogs remain active until early October.
Bullfrogs lack the dorsolateral folds characteristic of other species of true frogs found in Ohio (Fig 23). The sex of adults can be readily determined by examining the diameter of the tympanum relative to that of the eye; in males the tympanum is much larger than the eye, while in females it is equal to or smaller than the eye. During the breeding season the throat of male bullfrogs has a yellow wash whereas that of females is white.
• Dorsolateral folds are absent in the bullfrog.
• The bullfrog is the largest species of frog that occurs in Ohio. It typically has spots or blotches scattered about the back.
• Color varies from olive brown through shades of green.
• Adult male bullfrogs have a yellowish wash on the throat and a tympanum much larger than the eye. Females have white throats and a tympanum equal in size to the eye.
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| Fig. 22. Tadpole of the bullfrog |
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Territorial males call to attract potential mates and to proclaim their territories. The fertilized eggs, averaging 1.3 mm in diameter, are laid in a pancake-like surface film. The 20,000 eggs produced by a single large female hatch in four days or less in the warm summer waters. Tadpole development is comparatively slow, and one to three years are required for them to achieve the 70-140 mm length usually attained before transformation (Fig. 22). The climate in Ohio requires them to spend one totwo winters in the larval stage. Two to four years are necessary after transformation for bullfrogs to reach sexual maturity. In the wild a bullfrog may have a longevity of seven to nine years, but the record in captivity is 16 years.
• Bullfrog tadpoles are olive on the back and sides. The body, tail musculature, and tail crests are dotted with small dark spots having distinct, sharply defined margins.
• The bullfrog requires one to two winters in Ohio in the larval stage before transforming to a juvenile frog.
• Development of the tadpole is comparatively slow, and one to three years are required for larva to attain a total length of 70-140 mm before transformation.
Male bullfrogs have paired vocal sacs. Their deep sounding, low frequency, bass fiddle-like calls can be heard booming over a distance of one kilometer from breeding sites throughout Ohio (Fig. 24). The sound is reminiscent of a bull bellowing in the distance.
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Fig. 24. Call of the bullfrog |
Call of the bullfrog (46 seconds, 365 KB)
Excerpt (12 seconds, 94 KB)
• The call of the bullfrog is low in pitch and sounds similar to a bass fiddle or a bull bellowing in the pasture.
• The dominant frequency of the call in the spectrogram is 300 Hz, and the call duration is 0.6 seconds.
• Calls of bullfrogs, green frogs, a single spring peeper, and a distant common gray treefrog are heard in the background.