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Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

April 1996

All about amphibians

Whether collecting eggs, or looking under logs for wrigglers and hoppers, it's fun to poke around the pond for frogs, toads and salamanders.

Dreux J. Watermolen

Ah spring! For tree or toad, the sap is running, there's love in the air and it pays to advertise.

Like birds, frog and toad species each have a distinctive call to attract females to breeding areas. In the shallow waters fertilized eggs will hatch into tadpoles and metamorphose into young frogs. We can help you get to the right place at the right time to hear and see the annual ritual. Perhaps you will collect a few amphibian eggs that you can hatch out at home.

It's fun to explore for other amphibians too. On that first rainy night in late March before the ground thaws, about the time the chorus frogs begin calling, salamanders will also start making their moves. They make a nocturnal migration from upland wooded areas to ponds, marshes, and lakes. Male salamanders do not have breeding calls. They simply show up at the breeding areas a day or two after the females to start active courtship.

A key to enjoying Wisconsin's amphibians – eleven native frogs, one toad, and seven salamanders – is knowing how to find them. It's likely that several species live near your house. Start by scouting nearby wetlands. Almost all of Wisconsin's amphibians need water for breeding. Some breed in temporary ponds that form in farm fields, some only inhabit lakes and perpetually wet areas, others use woodland pools.

Next, slowly walk or cruise rural roads that separate upland areas from ponds and marshes. By driving slowly just after dark with your headlights on or walking the road with a flashlight, the lights might spot the glistening bodies of migrating salamanders. Adult amphibians can be safely handled, provided your hands are clean and free of bug spray.. Always wet your hands before touching amphibians, so you don't rub off the mucous membrane that keeps them from drying out and protects them from germs.

Timing visits to hit the peak

Shortly after the chorus frogs begin to sing, northern leopard frogs, northern spring peepers, and wood frogs join in. Later in the spring American toads, and Cope's and eastern gray treefrogs can be heard. Green frogs, mink frogs, and bullfrogs start croaking in the very late spring and early summer.

Salamander species also migrate throughout the spring. You are more likely to see tiger salamanders first because they are large and populations are widely distributed in Wisconsin. Blue-spotted and spotted salamanders follow shortly after. By May, you may encounter several species at the same time.

The result of all this calling and migrating is massive, frenzied breeding in Wisconsin ponds and marshes. Millions of amphibian eggs are laid and fertilized. Wisconsin amphibians lay moderately-sized eggs surrounded by a thin membrane and one to three concentric gelatinous capsules, depending on the species. As eggs are laid, the capsules swell and the outermost form a protective jelly.

As you search the pond, note the variety of egg masses. Pickerel frogs and spotted salamanders enclose many eggs in a single jelly mass. Central newts and spring peepers deposit eggs singly. The American toad's eggs and jelly are shaped in long, paired strings. Some salamanders deposit their eggs in several small packets. Clumps of eggs are commonly attached to sticks or vegetation to hold their position in the pond or stream. Bullfrogs and green frogs lay eggs in a film on the surface of still, shallow waters. Eggs laid in a surface film are more vulnerable, but are better able to meet their oxygen needs from being exposed to the open air.

Two species of Wisconsin salamanders lay their eggs in terrestrial environments. Redback salamanders lay their eggs under logs and stones in hardwood forests, and four-toed salamanders lay their eggs in Sphagnum moss or other moist substrates in bogs and along streams.

Individual females can lay enormous numbers of eggs. In general, larger species have more eggs than smaller ones, and salamanders lay fewer eggs than frogs do. Giant bullfrogs can lay up to 20,000 eggs, while the tiny gray treefrogs will lay as few as 10. Blue-spotted salamanders will lay from seven to 40 eggs, but spotted salamanders will lay as many as 250.

Most amphibians emigrate from the breeding ponds after mating, leaving the eggs unprotected. A few salamanders, however, provide parental care. Redback salamanders guard their eggs from potential predators. The female often encircles the eggs with her body and aggressively defends the nest. Secretions from her skin rub onto the eggs to retard bacterial and fungal development. Four-toed salamanders often lay their eggs in communal nests which are tended by the females. Mudpuppies guard their eggs which are attached singly to the underside of rocks or other objects in shallow water.

Now that you know where to look, here's what you are looking for. Amphibian eggs are usually easy to find. The egg yolk is creamy yellow or pale grayish yellow. Egg masses that are exposed to direct sunlight develop dark pigment on the exposed side. The pigments may protect the developing embryo from ultraviolet radiation. Perhaps the adaptation allows eggs to absorb heat faster and keeps them warmer for a longer time than single, light-colored egg masses. Eggs laid in warm, shallow, temporary ponds usually develop quicker than those laid in colder, deeper waters. The gelatinous masses surrounding the eggs often appear greenish as algae grows in the membranes.

Eggs may hatch in a few days or take several weeks depending on the water temperature. The tadpoles and larval salamanders which emerge feed voraciously. Most tadpoles and salamander larvae metamorphose into adults after several weeks, others take their time. Salamanders become adults by late summer so they can leave the breeding ponds for upland habitats. Bullfrog, green frog, and some mink frog tadpoles take a year or more to develop into frogs. Mudpuppies never loose their larval characteristics.

The central newt has a life history distinct from other Wisconsin salamanders. In August, newt larvae metamorphose and adapt for aquatic or terrestrial life depending on the surrounding habitat and climate. If a pond dries up, aquatic newts lose their high tail fins, change color from green to brown, and maintain a terrestrial life as "efts". If the pond later fills up, the efts transform back to the aquatic stage, though they don't develop gills. The newts can oscillate between these modes of life as climate dictates.

Valued in ecosystems, economy and research

Amphibians are an important component in many ecosystems. Research in New England has shown that the mass of salamanders exceeds the bird and mammal life in some forests. Amphibians are the top predators in some aquatic habitats, consuming a wide variety of insects and other invertebrates. On the other hand, amphibians are also a favored food for a variety of fishes, reptiles, birds, mammals and other amphibians.

Amphibians wriggle and hop through the economy as well. Frogs and salamanders are collected,raised and sold by the biological supply, laboratory and pet industries. Newt and tiger salamander larvae are sold as fish bait. Frog legs are tasty fare at upscale restaurants and mudpuppy tails have been consumed as a delicacy.

Ecologists view amphibians as valuable indicators of environmental change. Since they spend part of their life in water and on land, amphibians are monitored and analyzed to measure the effects of water, air, and land pollution.

In the 1970s, scientists expressed concerns about declining leopard and cricket frog populations in Wisconsin. In 1989, concern about apparent worldwide declines in amphibian population warranted a symposium in Canterbury, England. Scientists from 63 countries relayed their research but there was no consensus that amphibian populations declines could be attributed to clearcut pollution sources or changing conditions. Scientists suspected a range of causes including greater ultraviolet radiation due to a thinning ozone layer, acid precipitation or wind-borne pesticides.

Experts convened by the National Research Council did not find a single factor to explain population declines. Rather, they suggest widespread destruction of amphibian habitat, changing land uses, competition from other species and natural causes such as drought are responsible for changing land uses, and competition from other species are all taking a toll.

Part of the difficulty is that estimating amphibian populations is a tricky business and research can send different signals. Here in Wisconsin, for example, spring peeper populations seem stable, and wood frog populations are increasing slightly. Leopard frog populations took a big dip in the 1970s, but now appear relatively stable. Documented declines of other species are indisputable. Locally, the endangered Blanchard's cricket frog waivers on the brink of extirpation.

Since 1981, the Wisconsin DNR has coordinated a statewide frog and toad survey, the oldest such survey in the nation. Approximately 100 volunteers scattered throughout the state visit 10 wetland sites three times each year to listen for calling frogs and toads. There is no similar organized effort to monitor salamander populations in Wisconsin. In spite of their environmental importance, most cold-blooded creatures generally don't attract the research dollars as readily as bird and mammal have.

The chorus of frogs in Aristophanes' ancient Greek play croaked "Brekekekex koax koax," as Dionysus rowed across the river Styx in the underworld. Their words may seem like gibberish, but a sudden, deathly silence from the amphibian world in spring would send a more sobering message.


Raising amphibians at home

Obtaining eggs and tadpoles: Ponds, small lakes and creeks are ideal places to find amphibian eggs and catch tadpoles. Use small dip nets or jars to collect eggs and tadpoles and transport them home in clean jars, plastic bags or plastic containers. Keep the container in an insulated bag or cooler to maintain the approximate temperature where the eggs and tadpoles were collected. Take an extra container of water from the waters where the specimens were collected.

Never remove eggs or tadpoles from public areas such as parks, refuges or conservation areas. Ask permission before removing tadpoles from private land. Also make sure you are not collecting eggs or tadpoles of the protected Blanchard's cricket frog. Only collect a few tadpoles and eggs and only take as many your bowl or aquarium can hold without over-crowding.

To collect frogs, tadpoles and salamanders, you need a valid fishing license or a small game license. Frog season opens on the Saturday nearest May 1 and runs through December 31 each year. You will find a short list of rules in the 1996 Spearing and Netting Regulations available at DNR offices and other license outlets.

Maintaining your catch: Eggs and tadpoles can be kept in a large, flat pan, fish bowl, aquarium, or a large glass jar. Set up the new home ahead of time. I recommend using water from the pond where you collect the eggs or tadpoles to give them a head start. Chlorinated tap water destroys bacteria and algae and it may kill amphibian eggs and larvae. Treat a jug of tap water with a dechlorinator you can buy at a pet store or let a jug of water stand a few days with the lid off so the chlorine can dissipate. Provide at least one gallon of water for every two tadpoles to prevent over-crowding, and use an air stone and air pump to provide a constant stream of fine bubbles. It is not necessary to provide sand or gravel.

Eggs found in submerged habitats should be kept submerged, and those found floating should be allowed to float.

Feeding tadpoles: Tadpoles usually eat algae and other minute plant matter, but this may be hard to get in sufficient quantities at home. Finely ground commercial goldfish food, a commercial trout chow, or algae from another aquarium should be fed twice daily. As a substitute you can boil and cool two tablespoons of fresh spinach or lettuce (not cabbage). If available, crush rabbit food pellets and feed them to tadpoles as a dietary supplement. Small flakes of hard-boiled egg yolk can be added twice a week as a protein supplement.

Feed only what they can eat in a hour to avoid fouling the water. Remove any uneaten food.

As tadpoles become frogs, their diet changes from eating plants to feeding exclusively on live animals such as insects and small crustaceans. It's a real challenge to find enough food to maintain most juvenile frogs for very long. Tiny mealworms or aphids from infested houseplants are your best bet.

Tadpole transformation: Tadpoles undergo three remarkable changes that are easy to observe. First, they grow legs – back legs first; front legs last. Second, they slowly lose their tails. As the front legs grow, the tadpoles will no longer eat. The tail shrinks as the tissue is reabsorbed as food by the tadpole. Finally, the tadpole switches from breathing with gills to breathing with lungs after it grows legs.

Once the amphibian's hind legs appear, you need to rework the landscape in its container. Provide a gently sloping place where they can crawl out of the water. When the froglets are ready to leave the water, they must be able to do so quickly, or they may drown. A small pile of rocks is fine. Driftwood also works, but avoid all types of treated lumber.

Returning frogs to their homes: After you complete your observations, release the young frogs back into the wild where you originally collected them as eggs or tadpoles. Do this before the end of September so they have time to find places to hibernate for the winter. Do not release animals that were not collected in Wisconsin or are not naturally found here. Introducing species that are not found here could jeopardize other native species. It's against the law for a good reason.

A tragic example of how introduced species affect native amphibians occurred in Calaveras County, California. The celebrated jumping frog of this locale is now extinct. Those not eaten by gold miners in the 19th century were eaten by the eastern bullfrogs that were brought West for food and hunting in the 20th century.


What's a salamander?

Nearly everyone is familiar with frogs and toads, but fewer people recognize salamanders.

Like frogs and toads, salamanders are amphibians. They are sometimes confused with lizards which are reptiles that have scales on their bodies and claws on their toes. Salamanders have smooth or warty skins and are clawless. They are small animals with backbones and moist skins. Most cannot travel very far from water and most lay many jelly-like eggs in water. Their eggs hatch into gilled larvae that look similar to small fish.

The greatest variety of salamanders inhabit North and South America. In Wisconsin, we have seven species which are fairly easy to identify. Some older references list an eighth species, Tremblay's salamander, but scientists found this species to be a genetic variation of the blue-spotted salamander.

Juvenile salamanders, unlike tadpoles, have bushy gills and projections near their neck called balancers which help them maintain upright positions in the water. As the larvae mature, salamanders absorb their gills and develop lungs and feet.

Every family has its exceptions, and Wisconsin's salamanders have two: the mudpuppy retains its large, bushy red gills and keeps its larval features throughout its lifetime. Redback salamanders breed terrestrially. They never develop gills and look like miniature adults when they hatch.


Wisconsin amphibians

Toad
eastern American toad (Bufo americanus americanus)

Frogs
Blanchard's cricket frog (Acris crepitans blanchardi)
chorus frog (Pseudacris triseriata)
northern spring peeper (Pseudacris crucifer crucifer)
Cope's gray treefrog (Hyla chrysoscelis)
eastern gray treefrog (Hyla versicolor)
bullfrog (Rana catesbeiana)
green frog (Rana clamitans melanota)
pickerel frog (Rana palustris)
northern leopard frog (Rana pipiens pipiens)
mink frog (Rana septentrionalis)
wood frog (Rana sylvatica)

Salamanders
blue-spotted salamander (Ambystoma laterale)
spotted salamander (Ambystoma maculatum)
tiger salamander (Ambystoma tigrinum)
central newt (Notophtalmus viridescens louisianensis)
four-toed salamander (Hemidactylium scutatum)
redback salamander (Plethodon cinereus cinereus)
mudpuppy (Necturus maculosus maculosus)


Useful references about amphibians

The following books and reports, available at your local library or book store, can be consulted for additional information about Wisconsin's amphibians and can be used to identify species you encounter.

  • Natural History of Amphibians and Reptiles in Wisconsin by Richard C. Vogt. Milwaukee: Milwaukee Public Museum. 1981.
  • A Field Guide to the Amphibians and Reptiles of Eastern and Central North America by Roger Conant and Joseph T. Collins. (Peterson Field Guide Series). Boston: Houghton Mifflin. 1992.
  • Amphibians of North America by Hobart M. Smith. (Golden Field Guide Series). New York: Golden Press. 1978.
  • "A Key to the Eggs of Wisconsin's Amphibians" by Dreux J. Watermolen. Madison: Wisconsin Department of Natural Resources. Research Report No. 165. 1995.
  • Handbook of Frogs and Toads of the United States and Canada by Albert H. and Anna A. Wright. Ithaca: Comstock Publications. 1949.
  • Handbook of Salamanders by Sherman C. Bishop. Ithaca: Comstock Publications. 1943
  • Amphibians and Reptiles Native to Minnesota by Barney Oldfield and John J. Moriarty. Minneapolis: University of Minnesota Press. 1994.

Dreux J. Watermolen is a terrestrial biologist who analyzes the environmental consequences of proposed projects for DNR's Bureau of Environmental Analysis and Review.