Israel's green toad population recently joined other local amphibian species on the endangered list, after Tel Aviv University's zoology department conducted a four-year review of the green toad population in pools and shallow water in coastal Israel.

During the winter months, the toads lay long chains of thousands of eggs in shallow bodies of water such as winter pools, where they hatch into tadpoles that evolve into adult toads. One aspect of the research tracked the number of toads that successfully completed this life cycle.

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Professor Avital Gazit and two students, Eldad Elraon and Shai Levy, began to suspect that manmade water sites were confusing toad parents, who mistakenly identified them as appropriate sites for egg laying. These sites included drainage ditches, fields flooded by rainwater and various dig sites. Water in all these areas dries up very quickly, long before the 12 weeks the tadpoles need to develop.

In order to test their theory, the researchers deepened a flooded area on Kibbutz Gan Shmuel, where the entire tadpole population had died in the past. "After the digging, the site became a prosperous and successful reproduction site," Gazit said.

Gazit said it is now evident that manmade shallow pools have become a deadly ecological trap for thousands of tadpoles. "The toad cannot differentiate between appropriate and inappropriate water sources," Gazit explained. "At one time, [the latter] were a relatively small portion of the toads' options. But we changed the situation by drying up many natural winter pools and increasing the number of shallow water bodies. As a result, young toads do not join the population, which is shrinking."

The researchers said that this factor had not previously been identified as a reason for Israel's declining amphibian populations.

The researchers recommended adopting a policy of drying up flooded agricultural land and other areas of shallow water. Alternatively, "an area of about a quarter dunam can be deepened on a slight slope to a depth of one meter, which would allow the water to last for three months, saving the amphibians," Gazit said. "Farmers are not harmed, as the area needed is so small, and since it consists of space that floods in winter, it cannot be worked during that season anyway."