Bullfrogs

Description

Typically, bullfrogs reach up to eight inches in length (measured from snout to vent), but larger specimens occur in some areas. The overall coloration is green or gray brown with brown spots, especially on older specimens. Some brown, yellow, albino and even blue individuals have been observed. Adults have a conspicuous round eardrum, called the tympanum, located on either side of the head. The tympanum is up to twice as large as the eye. A ridge of skin starts behind the eye, runs over the eardrum, and ends at the base of the front legs. There are no lateral ridges on the back. The hind legs are large and powerful and may be banded or blotched with brown. Males have a singular throat pouch that is pale to bright yellow. Females have a white throat. Tadpoles are drab olive green with many tiny black pinhead-sized specks scattered throughout the tail fin and on the back. They may grow up to five inches in length.

Distribution

Bullfrogs are perhaps the most widely distributed amphibian in North America. Originally, their range extended from Nova Scotia south to central Florida and west to the Rocky Mountains, but introductions into western lands (for instance, into Utah around the start of the 20th century) have confused the western extent of the original range. Today, bullfrogs are found across most of the lower 48 states as well as in Mexico, Cuba and Jamaica.

Habitat

Bullfrogs occupy permanent freshwater habitats such as ponds, rivers, lakes, reservoirs, marshes, stock ponds, ditches and irrigation canals. They may be found in deep or shallow water.

Call

Chorusing bullfrogs (males) make a deep "jug-o-rum" call during the day or night. When startled, bullfrogs – either sex and especially juveniles – make a sharp "eeep!" call. They hop to safety in a series of long leaps, their movement resembling a stone skipping across the water.

Behavior

Like many amphibians, bullfrogs tend to be quiet throughout most of the day. During daylight hours they may hide under vegetation or overhanging banks or sit in shallow water along a shoreline. As night falls, they leave their retreats and establish sites along the bank, in the water, or on floating logs from which the males call.

Males establish territories and may defend dozens of square feet of territory from other males. Sometimes, males compete vigorously for territories. A challenger will chorus. The resident male will give a "hick" call. The challenger may respond with this same call. A battle begins! The two may wrestle, trying to gouge each other with their thumbs. The winner may even hold the loser underwater, but will eventually let the loser up, then chase him from the territory.

In the fall, bullfrogs will burrow into the mud or soft soil until spring. Typically, adult bullfrogs retreat to winter burrows earlier than the juveniles. In the South, bullfrogs may remain active year-round, except during cold spells.

Breeding

Bullfrogs, unlike many other North American aurans, remain reproductively active throughout much of the summer. The breeding season, depending upon temperature, may extend from March through August. Air temperatures above 77 degrees Fahrenheit and with water pH levels (a measure of the acidity or alkalinity of the water) above 4.3 are necessary for successful reproductions, along with water temperatures between 68 to 86 degrees Fahrenheit. Bullfrogs may put in an appearance, however, when water temperatures reach 55 to 60 degrees Fahrenheit.

While a male typically remains sexually active throughout the summer, a female bullfrog generally lays only once a year, producing as many as 20,000 eggs at a time. The egg masses are huge, resembling semifloating mats of small bubbles. The masses are attached by "strings" to submerged vegetation. Although the females lay their eggs in the warmer months of summer, they deposit the eggs in the cooler portions of the pond. Water temperatures above 82 degrees Fahrenheit may cause the eggs to develop abnormally.

Food Habits

Bullfrogs generally sit and wait for a meal to pass or land nearby. They lung or leap forward with mouths open wide to catch prey. The bulk of a bullfrog's diet is insects, spiders, crayfish and other invertebrates, but they may also consume mice, small turtles, fish, snakes (including rattlesnakes), birds and other amphibians. A bullfrog will eat about anything it can get in its mouth.

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