Kihansi spray toad

© Michael Dick

On a Saturday afternoon the Reptile House at the Bronx Zoo is overflowing with children. They eagerly peer into exhibits displaying crocodiles, snakes and lizards. What they don’t see is the zoo’s colony of one of the most endangered species of frogs in the world, kept from public view on the second-floor of the building where their fragile existence won’t be disturbed.

Held in hermetically sealed terrariums, the  colony of Kihansi spray toads is fed fruit flies bred on site and treated to 14 timed-intervals of misting through spigots of specially filtered water. The mist simulates the effects of the waterfall in the river gorge where the miniature toad–adults measure three quarters of an inch–came from. Indeed, before the species disappeared from the Tanzanian gorge in 2002, they inhabited  the smallest geographic range of any known vertebrate species, just two square hectares in the spray zone of the waterfall.

The 10’ by 10’ room holding the terrariums the toads now inhabit is essentially a modern day “ark,” designed to rescue the frogs from the habitat destruction and disease that has destroyed their habitat in Tanzania. Around the world, the use of these kinds of “arks” has become increasing popular as a last-ditch conservation strategy. Biologists hope that by bringing severely endangered animals in from the wild and keeping them in zoos, aquariums or captive-breeding sites, they can keep them at sustainable population levels until a long-term solution to overwhelming problem of species extinction is found.

This is especially true in the case of amphibians species, whose numbers have dropped dramatically in recent decades from habitat destruction and a mysterious disease called chytrid fungus. Whereas 3.8% of mammal species and 1.8% of bird species are critically endangered, 7.7% of amphibian species are at a point of imminent extinction today. Over half of the world’s 6,000 plus amphibian species are at risk of endangerment, according to the World Conservation Union. In response to these grim statistics, an initiative called “Amphibian Ark” was launched by a group of biologists to try and bring 500 of the most critically endangered frogs to zoos and keeping them in biologically secure environments until they can be reintroduced to their habitats.

The amphibian crisis belies a greater catastrophe facing animal species around the world: Because amphibians are extremely sensitive to changes in their surroundings, they are considered by some biologists to be barometers of environmental health. As frog numbers plummet and whole populations disappear, many worry that this is the merely a warning sign that the massive species extinctions around the world caused by pollution, habitat destruction and infectious disease are speeding up and may become irreversible.

“We’re the first ones to admit this is the last ditch solution,” said Kevin Zippel, one of the founders of the ark initiative. “If Amphibian Ark is successful but only we’re successful, then we will have failed because we will have all these species in captivity permanently. We have to fix the threats in the wild or we won’t have anywhere to return these species to.”

Today, the likelihood that the Kihansi spray toad can be returned to the wild is slim. Their fate was largely determined in 1994, when the World Bank helped fund a $275 million project to construct the Lower Kihansi Hydropower Project in south central Tanzania, which would help fulfill the need for electricity in local communities and mining industries. Within four years, over 80% of the falls’ water was being diverted by the dam, forcing the tiny toads to congregate in the thousands at the base of the waterfall. Artificial misters were installed to try to preserve some of the spray zone but the damage to the habitat was compounded by periodic flushings of the dam, which are believed to have brought pollutants and possibly chytrid fungus into the falls.

In November of 2001, American biologist Jason Searle and a colleague traveled to Tanzania on a rescue mission, collecting 500 spray toads from the falls and transporting them to New York City. “When they were first brought in, the idea was to send them all over to zoos,” said Jenny Pramuk, an amphibian expert who cares for the toads at the Bronx Zoo. “The problem was nobody knew how to take care of them. No one had worked with them before. It took a few years to figure out how to breed them, the right mist cycle. At one point all the toads were recalled back to the Bronx and we were down to 60 individuals.”

Today, the colony of the Kihansi spray toads is split between the Bronx and Toledo zoos and is considered to be at a relatively stable level. Efforts are underway to train Tanzanian biologists so that the species can be returned to their native country and placed into yet another “ark.” But even after millions of dollars spent, cooperation by dozens of environmental agencies, and research conducted by amphibian experts and conservation biologists around the globe, it remains to be seen whether this tiny toad can ever survive in the gorge where it originally evolved.


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