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Inviato da Wes von Papinešu on Maggio 14, 2000 at 17:31:56:
YOMIURI SHIMBUN (Japan) 09 May 00 Nature in short - Frogs live, sing in harmony (Kevin Short)
With the Golden Week holidays over, salaried workers are returning from their native homes in the countryside to their jobs in the cities. Some of them will look more tired than when they left. This is because they probably spent most of the vacation helping their aging parents transplant rice seedlings into their paddies.
The rice seeds were planted in special beds in early April and, by the end of the month, had sprouted and grown to a height of 10 centimeters or so. Next came the work of preparing the paddies and transplanting the seedlings.
To begin with, the paddies were filled with water, then worked over with a special tractor attachment that churns up the top layer of mud and smoothes the surface. The final step, two or three days later, consisted of transplanting the seedlings, a task accomplished with an amazingly clever tractor attachment that picks the rice seedlings from a dense mat and sticks them right into the mud, usually four to six rows at a time.
When the workers returned to their jobs, they left behind them a completely transformed countryside landscape. Before the holidays, the paddies were covered with buttercups and bitter cress. Now they are shallow marshes with sparking water and neat rows of thin rice seedlings.
In addition, the rice paddy countryside was relatively quiet before the holidays, but now the late afternoon and evening air is filled with a great chorus of frog song. In the Kanto countryside, at least three species can be heard singing away at once.
One song is a loud, persistent "gwah-gwah-gwah-gwah-gwah," while another is a series of sharp, staccato notes with a Latin beat. The third is a Woody Woodpecker-style "eht-eht-eht-eht-eht-eh."
The "gwah-gwah" is the little Japanese Tree Frog (Hyla japonica), called amagaeru (rain frog) in Japanese for its tendency to sing loudly in damp weather. The Latino serenade belongs to the Schlegel's Green Tree Frog (rhacaorpus), called Shuregeru aogaeru in Japanese, while the Woody Woodpecker is our local Tokyo Daruma Pond Frog (Tokyo darumagaeru; Ranus).
One wonders how all these frogs can mate and spawn at the same time without getting in each other's way. The trick is in specialization. Over the centuries, each species has evolved to prefer a slightly different breeding habitat.
The Japanese tree frog, for example, lays its eggs directly in the paddies. The eggs float and drift across the water surface, usually collecting in small bunches around the young rice stalks. In contrast, the green tree frog scoops out a little depression in the side of the aze dikes that separate the paddies. The eggs are deposited inside the depression and encased in a white foam mass about the size of a tennis ball. When the eggs are ready to hatch out, the foam mass disintegrates and the tadpoles drop into the paddy.
As a result, the eggs and tadpoles of the Japanese tree frog tend to stay out in the center of the paddy, while those of the green tree frog are concentrated along the edges. The pond frog avoids competition with these two species by preferring to mate and spawn not in the paddies themselves, but in the narrow irrigation canals that carry water to and from the paddies.
In some areas, a fourth frog melody may be added to the chorus. This is the deep, soulful bass song of the American bullfrog, an introduced species. The bullfrogs, however, avoid both the paddies and irrigation ditches, preferring to live and breed in the little tameike irrigation ponds that often sit at the head of the narrow valleys, where water seeps out of the surrounding slopes.
As if four species of singers were not enough, a country walker will soon notice that the paddies, ditches and ponds are already teeming with fairly large tadpoles, some already starting to lose their tails and grow legs. These are either Japanese Toads (hikigaeru; Bufo japonicus) or Japanese Brown Frogs (nihon akagaeru; Ranus japonicus).
The brown frogs breed mostly in the rice paddies, but they lay their eggs in late February and early March. By the time the tree frog eggs are hatching out, the brown frog tadpoles are ready to leave the paddies for the surrounding woodlands, where they spend most of their time.
These brown frogs, however, are dependent on natural rainfall to keep the paddies wet during March and April and thus can have their entire brood wiped out if the weather does not cooperate. Unfortunately, this year was not a very good one for the brownies.
The toads also occasionally breed in the paddies, but they prefer the canals and ponds. They lay their eggs in late March and early April, a month after the brownies but a month before the rest of the crew. Right now their little dark-black tadpoles are just getting ready to transform. Soon they will crawl out of the water and head for their favorite habitats, forest floors and the grounds around temples, shrines and farmhouses.
By spawning in different habitats or choosing different times of the year, these six species of frog can live peacefully together in a narrow stretch of rice paddy countryside. Hopefully, the tired workers will be cheered to know that the local frogs greatly appreciate their efforts!
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