Friday, July 18, 2003
When and where seen: On the Town Green on the 4th of July along with many other bullfrogs and green frogs competing in the frog-jumping competition. The photo is of the champion jumper. It was caught by Katie Zinke in a large pond in her back yard on Concord Street. Bullfrogs can be heard making their low frequency "jug-o-rum" advertising call from various ponds around town. You are most likely to find one in a pond where the vegetation both in the water and around the edges is particularly lush.
Characteristics: Bullfrogs are greenish, brownish, yellow, sometimes albino, and even occasionally blue. Adult bullfrogs can reach up to seven inches from nose to tail. Bullfrogs have a short ridge of skin that starts behind the eye, goes over the eardrum, and ends near the base of the front legs. They can be distinguished from green frogs in which the ridge of skin runs all the way from the eye down each side of the back to the hind end. Male bullfrogs have yellow throats and ear drums that are larger than the diameter of the eyes. Katie's champion jumper was a male as was the runner-up.
Life cycle: A female bullfrog lays, on average, about six to seven thousand eggs per year. The tadpoles hatch in about two weeks and spend most of their time feeding. Some will complete their metamorphosis the following summer and others in the second summer. In the spring, the bullfrogs become active when the pond-bottom temperatures reach 55 · 60 degrees F. Adult frogs continue to grow throughout their lives. The largest and oldest are likely to be females. The males lead an active life defending their territories and are more exposed to predators · and to children looking for an entrant in the frog-jumping contest. (Everyone I spoke to at the frog-jumping contest was planning to return their frog to its pond.)
Food: Bullfrogs get their food by using a "sit-and-wait" method but in a less disciplined way than in your average restaurant. When something tasty goes by, the bullfrog's long tongue darts out and grabs it. The bulk of the diet is insects and other invertebrates, but bullfrogs also eat mice, small turtles, fish, and other frogs.
Survival of the species: Bullfrogs are becoming increasingly common in waters where pollution has raised the water temperature and increased the aquatic vegetation. They are able to thrive in higher water temperatures than most other frogs. They also have a long breeding season and the very large tadpoles have a higher pre-metamorphic survival rate than other frogs.
References: Thomas F. Tyning, Stokes Nature Guides, Guide to Amphibians and Reptiles ; University of Michigan Museum of Zoology at http://animaldiversity.ummz.umich.edu.
© 2003 The Carlisle Mosquito