As mid-summer approaches with the arrival of July and water temperatures in ponds, lakes, and streams begin to rise, a low booming sound that resonates from bodies of water will be heard. This sound, a loud “jug-o-rum” that can travel for 1 kilometer from its origin, is the mating call of the Bullfrog, Rana catesbeiana.
Bullfrogs are big. A common activity for kids in the summer who are swimming in lakes and ponds is to have competitions for who can spot the fattest, roundest one. Bullfrogs are the largest anuran in North America. (An anuran is any organism within the order Anura of the class Amphibia, which comprises the frogs, toads, and tree frogs. All anurans lack a tail in the adult stage and have long hind limbs evolved for leaping and swimming). Both male and female adults can reach a length of six to eight inches from nose to foot! Given the size and the aggressiveness of this amphibian, another organism would not want to encounter a bullfrog if they were an insect, small mammal, rodent, bird, or even a turtle. Bullfrogs are extremely assertive critters with large appetites, whose diets consist of the aforementioned animals, along with snakes, fish, tadpoles, amphibious eggs, and other frogs, which classifies them as cannibals. All of the species that comprise the diet of the Bullfrog can be found in the habitat where the Bullfrog lives.
The bullfrog’s habitat, like the habitat of many amphibians, is a moist environment. More specifically they inhabit the edges of ponds, lakes, streams, and slow-moving rivers, where vegetation is abundant and necessary for camouflage and protection. The only requirement of the bullfrog is that it must live in a permanent body of water. This means that the water is present throughout the year and never completely evaporates like the water in an ephemeral vernal pool or a semipermenant pond, for example. In a permanent body of water the bullfrog can find and eat most of the species that it needs to survive, but in a nonpermanent body of water, many of these species are missing.
Aside from eating, bullfrogs reproduce. They emerge in the spring in middle to late May, but they remain silent until middle to late June and July when they start calling for female mates, and the “jug-o-rum” sound echoes. The bullfrog mates the latest in the year in comparison to other frogs, because the bullfrog must wait until water temperatures reach between 68 and 72 degrees Fahrenheit. Male bullfrogs will defend their territories during breeding time for up to twenty inches in diameter. Large males defend more valuable locations where the survival rate of the eggs is high. A batch of eggs within an envelope of clear jelly is laid singly, usually inside the territory of the male who bred with the female laying the eggs. The jelly protects the eggs from predators like fish and other frogs and allows them to float as a thin film of about two inches in diameter, on the surface of the water. Every batch of eggs can contain between 12,000 and 20,000 black and white-colored eggs!
Bullfrog eggs hatch within three to five days, but development from the larval or tadpole stage to the adult stage takes 3 years! Tadpoles can be easily spotted along the edges of ponds, lakes, streams, and rivers, where plant material and algae are abundant for feeding, as they are primarily herbaceous feeders. The tadpoles are a light to dark mottled green or brown, with bronze bellies. First season larvae that hatch in July of the summer when their eggs are laid grow to be one to one-and-a-half inches long. Second season larvae (one year after egg laying,) grow to be three to three-and-a-half inches long. Third season larvae (two years after egg laying,) grow to be four to six inches long, and have well-developed hind legs. These tadpoles are beefy and robust, just like the adult frogs that they develop into.
Bullfrogs are interesting animals that are fun to observe and listen to. They can add a lot of character and feeling to a summer evening. Please remember to respect these frogs and other wildlife so that other people can appreciate them too! Interested in learning more about animals in the summer? Join a Naturalist Guide at the AMC’s Pinkham Notch Visitor Center for a guided walk or hike. Call ahead (603-466-2721) for program times and details. Have a natural history question that you would like answered in this blog? Send out an e-mail to firstname.lastname@example.org.
Sources for this blog:
Burne R., Matthew, Kenney P., Leo, A Field Guide to the Animals of Vernal Pools
Hunter L., Malcolm, et al, Maine Amphibians and Reptiles
Tyning, F., Thomas, Stokes Nature Guides, A Guide to Amphibians and Reptiles
NH Fish and Game website