Bullfrogs

Croak! Croak! Croooooak!  I live on a pond, and for the last week has it has belonged to the bullfrogs, Rana catesbeiana. The bullfrog is the largest species of frog in North America, and the ones in my pond are no exception.  Bullfrogs are green, yellow-green or brown with dark splotches on the back and dark leg bands.  The tympanum, or eardrum is immediately behind their eye.  On male bullfrogs, the tympanum is larger than the eye, and their throats are pale turning to dark yellow when breeding; on female bullfrogs, the tympanum is the same size as the eye and their throats are whitish.
 

Their preferred habitat is still, permanent bodies of water, with plenty of submerged and emergent vegetation.  Bullfrogs hibernate over the winter in the mud at the bottom of these permanent pools.  They like warmer water and generally will not emerge in spring until water temperatures are in the 15^C (60^F) range.   

Breeding, mating & calling activities start in late May and extend well into July.  Bullfrogs are normally active from early evening all through the nighttime hours, and may extend activities into the daytime.  They are most active on warm nights.  Males sit in the shallows or along the banks and create a low-pitched brrr-rum call to find a mate.  Males are territorial establishing an area roughly 5′ to 20′ in diameter that they actively defend from encroachment by other males.  Within the same pond, several males may have bordering territories, and neighbors will also aggressively object to a new frog attempting to take over an existing territory.  Larger males will establish themselves in the choicest sites hoping to lure females to an area good for egg-laying. 

The female deposits from 5,000 to 20,000 eggs in a thin-mucus covered, floating mass that may be from a foot to three feet in diameter.  Eggs will hatch in three to six days into tadpoles.  Tadpoles spend from one to two years living in the pond, feeding on algae or decaying material until metamorphosing into froglets in their second or third summer.  Bullfrogs become sexually mature in two to four years, and their lifespan is six to eight years.

Bullfrogs will eat nearly anything they can swallow including fish, snakes, turtles, other frogs, birds and small mammals, but the majority of their diet consists of invertebrates including dragonflies, beetles, insects, spiders, snails and crayfish.  Bullfrogs are also prey for fish, snakes, turtles, herons, otters, racoons and mink.  They are extensively hunted by man for the food industry, especially frog legs.  If threatened, they are equally comfortable on land and water and may flee to either habitat.  When caught, they emit a loud wailing scream that often times startles the predator and allows the bullfrog to escape.

In recent years, the pond behind my house has been naturalized with native vegetation.  The bullfrog population as well as many other species have responded very favorably to these efforts.  However, in many other areas, habitat loss, water pollution and  pesticide runoff have all been factors in the declining populations of bullfrogs and other amphibians.  Removal of shoreline vegetation for real estate or recreational development has damaged a number of breeding sites.  You can help by supporting efforts to keep local ponds, lakes and other wetland sites natural and undisturbed.