Everyone’s favorite sound around a lake is a bullfrog. Ever wonder if bass eat frogs? Tie on a Ribbit, or similar frog-style lure, and experience memorable angling action.
Frogs inhabit large, permanent water bodies and usually are found along the shoreline. Their call is reminiscent of a bull roar, which gives the frog its common name. Bullfrogs are native to southern/eastern parts of the United States and Canada. They have been widely introduced across North, Central, and South America, Western Europe, plus Asia. Although highly prized throughout our region, in some areas they’re regarded as invasive species.
Teeth are tiny and useful only for grasping. Eyes are prominent with brown irises and horizontal almond-shaped pupils. Eardrums are easily seen behind the eyes. Limbs are blotched or banded with gray. Forelegs are short and sturdy. Hind legs are long and strong. Front toes are not webbed, but back toes have webbing between digits. Males are smaller than females and have yellow throats. Males have tympani (eardrums) larger than their eyes, while the females’ is about the size of her eyes. Tympani enable frogs to hear above and below water. Bullfrogs grow fast in the first eight months of life. Mature weight may be 1.1-pound. In some cases, they have attained 1.8 pounds and measured 8-10-inches in length. Breeding season typically lasts two to three months. A Michigan study showed males arriving at breeding sites in late May or early June and remaining into July. Territorial males occupy sites spaced four to 19-feet apart and call loudly. At least three different calls have been noted in males. These distinctive calls are made as threats to other males, advertisement to attract females, and encounter calls which precede combat.
Multiple studies note male behavior changes according to population density. Males gather in leks (large groups) to court females. This tactic is favored due to the difficulty in defending individual territories among large male populations. This variance causes differences in how females choose mates. When male population density is low and males maintain more distinct territories, female choice is mostly determined by territory quality. When male population density is higher, females depend on other cues to select mates. These cues include the males’ position within the chorus and differences in male display behaviors among other determinants. Social dominance within choruses is established through challenges, threats, and other physical displays. Older males usually acquire central locations. Younger males are restricted to the periphery.
Females lay a batch of up to 20,000 eggs among vegetation in shallow water. Eggs form a thin, floating sheet which may cover an area five to 10 sq. ft. Embryos develop best at water temperatures between 75 and 86 degrees and hatch in three to five days. If water temperature rises above 90-degrees, developmental abnormalities occur. If temps fall below 59-degrees, normal development ceases. Newly hatched tadpoles show a preference for living in shallow water on fine gravel bottoms since there may be fewer predators in these locations. As they grow, tadpoles typically move into deeper water.
Metamorphosis ranges from a few months in the south to three years in the north where colder water slows development. Maximum lifespan in the wild is estimated at eight to ten years, but one frog lived for almost sixteen years in captivity. Bullfrogs are voracious, opportunistic, ambush predators that prey on any small animal they can overpower and stuff down their throats. Bullfrog stomach surveys have found rodents, small reptiles, crawfish, birds, bats, and insects.
Bullfrogs are favored prey of many birds such as herons, river otters, predatory fish, and occasionally other amphibians. Eggs and larvae are unpalatable to many salamanders and fish, but high activity levels may make tadpoles more noticeable to a predator not deterred by their unpleasant taste. Many folks hunt bullfrogs and consume their legs. Traditional hunting methods include paddling or poling silently by boat in ponds or swamps at night or stalking on land. When hunters hear a frog’s call, a light is shone at the frog, temporarily inhibiting its movement. When close enough, the frog is gigged.