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Amazing frog metamorphosis!

Most of us have heard the loud jug-o'-rum of the bullfrog in the summer--but have you ever seen bullfrog eggs or, better yet, a bullfrog pollywog up close? If not, you're missing out on one of nature's most amazing transformations. Each year, the 14 species of frogs native to New York--including the bullfrog pictured--begin this cycle anew, and most of them complete their metamorphosis from gelatinous egg to a land-dwelling miniature frog within weeks. After hatching, the bullfrog and green frog pollywog may take two summers (or maybe even three in northern New York) to become pre-adult frogs. Wood frogs, which breed in March or April, will metamorphose by June.

Frog Life Cycle

The noisy mating choruses heard in spring and early summer are the beginning of a fascinating and complex life cycle that includes three key stages. First is the egg. Individual females often extrude thousands of eggs, which are fertilized in the water by males clasping females in a behavior called amplexus. Eggs hatch quickly, entering the aquatic larval or second stage, better known as the tadpole or pollywog. Tadpoles are typically herbivorous, scraping algae and other organisms off submerged surfaces. To avoid the constant threat of rapidly evaporating breeding ponds, predators such as aquatic insects, fishes and wading birds, tadpoles develop rapidly. A few species, especially in northern New York, will spend two summers as tadpoles, overwintering under the ice. The most complex transition occurs between the tadpole stage and the third, or adult stage. Completed during a short time period--sometimes in just three weeks--this miraculous transformation involves a developmental change from an aquatic, tailed, gill-breathing herbivore to a terrestrial, tailless, air-breathing, four-legged carnivore. Adult frogs eat a variety of things, including insects, worms, other frogs, or even newly hatched turtles.

Important Link

Frogs survive by taking advantage of the benefits of both an aquatic and terrestrial life. But they also suffer the problems associated with both systems: sedimentation that smoothers eggs, changes in water quality, fragmentation of upland habitats by roads, and even global issues such as acid rain and increased UV exposure. Diverse Dog populations comprised of large numbers of several species is usually a sign of a healthy habitat, and frogs in turn provide a significant food source to all the other wildlife that prey on them.

Where Can You See It?

To watch this wondrous event take place, begin by listening for a chorus of frogs in almost any nearby vernal pool, wetland or pond. Each species calls at a specific time of the year, beginning with spring peepers and wood frogs in late winter and ending with bullfrogs and green frogs--which call until mid-summer.

You Can Participate

If you'd like to become a citizen scientist, find a frog egg mass and keep a journal of what you see. Record important dates along the way, and sketch the stages of the frog life cycle, or take some photos. Next winter, you can share your journal with your friends, and you'll be the "neighborhood expert" when this exciting event returns!

For Further Reading:

Stokes Nature Guides: A Guide to Amphibians and Reptiles, by T.F. Tyning covers 27 of the 69 reptiles and amphibians found in New York and contains detailed information that cannot be found in a field guide. Species discussions include how, when and where to find each. Details on breeding habits, feeding habits, predation, behavior of the young, overwintering and other interesting information are included.

Some of the information in this article was adapted from the DEC brochure "Frogs and Toads of New York State." For your copy, write to: Conservationist re: NY Frogs, 625 Broadway, Albany, NY 12233-4502.

Alex Hyatt is assistant editor of Conservationist. He lives in Washington County.

Al Breisch is the Amphibian and Reptile Specialist for DEC's Division of Fish, Wildlife and Marine Resources.
COPYRIGHT 2006 New York State Department of Environmental Conservation
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2006 Gale, Cengage Learning. All rights reserved.

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Author:Hyatt, Alex; Breisch, Al
Publication:New York State Conservationist
Geographic Code:1U2NY
Date:Jun 1, 2006
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