Category: Amphibians & Reptiles – Frogs & Toads

The snow and ice of winter has disappeared, and temperatures are starting to warm.  Amphibian monitoring is one of the earliest conservation activities of spring.  Thirteen species of frogs and toads are found in the Chicago Wilderness region (southeastern Wisconsin, northeastern Illinois east of the Fox River, Northern Indiana, and southwestern Michigan).

Frogs and toads form a critical link in the food chains for both aquatic and terrestrial habitats.  They are prey for snakes, birds, mammals, and fish.  In addition, they are predators of invertebrates, insects, eggs, and small birds. 

The Calling Frog Survey, started in 1960, is a citizen science opportunity for volunteers to help identify the species of frogs in an area and gather information about them.  Results from several years of collected data identifies increases and decreases in population sizes and movement of large groups. 

All frogs and toads breed by laying eggs in an aquatic habitat.  Only males call, to attract a mate.  Various species start breeding at different times, the earliest are starting now and calling will continue  until the latest species ends its breeding season in mid-summer.  The frogs and toads of the Chicago Wilderness region are pictured below, along with links to listen to each species’ breeding call.

Listen for these wonderful songs when near any wetland habitat this spring.  If you would like to become a monitor, or want more information about monitoring or frogs in general, take a look at the frog calling survey’s website at Frog Calling Survey, and consider joining a monitoring group near you.

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.

As you are out walking at this time of year, whether in neighborhoods or natural areas, you may hear a musical trilling in the background.  This is the call of Bufo americanus, the American Toad, as it returns to the banks of local streams and ponds.  Male toads emit a high pitched trill that may last 30 seconds or more, as they actively seeking mates for breeding.  They call constantly during the daytime and early evening, and are often heard as part of the background sounds of the neighborhood.

American Toad, Tanya Dewey, Animal Diversity Web

The American Toad has a compact body with dry, warty yellowish-brown backs and sides.  They have short hind legs that allow them to walk or hop, but not take long leaps as do frogs. Adults are typically 2″ to 4″ with the females slightly larger than the males, but larger sizes up to 7″ have been observed in some localized areas.  These toads are found from the Mississippi River to the East Coast and from middle Canada to southern Georgia.

As in all frog and toad species, only the males call, hoping to attract a female by song alone.  American Toads like shallow, quiet waters with scant to moderate amounts of fully to partially submerged vegetation.  The male will select a stationary position in a desirable habitat, call, and after a female joins him, they will mate.  The female then lays her eggs in the water.  Breeding is often initiated by rainy days and warm evening temperatures.  A female will deposit between 2,000 and 20,000 eggs contained in two gelatinous strings of mucus several inches under the water’s surface and they may be attached to nearby vegetation. 

American Toad eggs by Judy Gallagher

Eggs hatch in 2 to 14 days depending on water conditions.  Tadpoles are black in color, and they will change into tiny toadlets in six to ten weeks.  Large groups of toadlets can be observed leaving the ponds for the open woodlands, prairies, marshes and your backyard.  The American Toad reaches sexual maturity in two to three years and may live ten years, although mortality from predators and human impact is high.

At this time of year, you may observe toads in your own backyard.  If you try to sneak up on a toad, especially in the evening, it will immediately stop calling if it hears you.  However, if you wait quietly at the edge of a pond for four to five minutes, the toads in the area will resume their singing.  Species are distinguishable by their song, and you can hear the different songs including the American Toad at the Illinois Natural History website: INHS Frog & Toad Calls.

If you should find a toad, see if you can observe some of the unique characteristics of these animals.  Do you see its ears?  They do not stick out from the head, as ours do.  Toads have a round patch positioned right behind their eye that is a tympanic membrane, able to detect and identify various sounds.  Can you observe it catching any prey?  Their tongues, which are long and sticky, are attached at the front of their mouths, not the back as ours are.  As insects fly by, a toad can flick its tongue out at an amazing speed to snare a meal.  You can watch this behaviors at Discovery News.

Spring Peeper – a lyrical name for a wonderful little singer in the woods at this time of year.  Most often heard in the late evening or through the night, these small frogs have some interesting traits.

They are hard to find due to their small size, 20mm-25mm or .8″-1″ when fully grown.  A little large than an adult’s thumbnail!  And their coloration provides wonderful camouflage from shades of brown, gray or olive skin.  The belly is cream or white, and the back is marked with a dark cross as well as darker bands marking the legs.

Spring Peepers are native to our area and can be found in marshy areas or light woods near freshwater ponds.  They are good climbers but prefer to stay near the ground, burrowing into leaf litter whenever it is available.  At this time of year, larger populations can be found near their preferred breeding habitat which is clear, clean freshwater ponds with no fish. 

Peepers breed in early spring time when males start to call for females in the early evening and on into early morning.  Only the males call.  And their call is a high pitched note which can be heard for several hundred yards in the woods.  And they are loud!  It is near impossible to have a conversation between two people when standing on the edge of a pond where a chorus of 8 or more of these tiny frogs are singing.  Click on the attached audio file to listen.

As you are out walking this spring, take a moment to stop by your favorite pond and listen closely for the sounds of spring.