In 1996, a group of scientists stepped into a small, nearly inaccessible gorge at the base of a waterfall on the Kihansi River in Tanzania. They found it teeming with tiny yellow toads whose robust chit-chitchit calls could be heard above the tremendous roar of the cascading water. Deep in their isolated territory, these newly discovered toads appeared to be abundant: the scientists estimated the population to be in the tens of thousands.
Kihansi spray toads are unique among amphibians because of their bright yellow color, diminutive two-centimeter size, and reproductive process: instead of laying eggs like most other amphibians, the females give birth to babies smaller than a grain of rice. Their habitat, about the size of four football fields, is among the smallest known ranges for any animal. Inside the gorge, the toads received a constant misting of water from the falls, which created a cool, moist climate with temperatures significantly lower than the surrounding areas.
In the late 1990s, a hydroelectric dam was constructed near the Kihansi Gorge to provide much-needed electricity to the region. But this changed the water flow and humidity of the unique spray zone at the base of the falls. In an attempt to mitigate these effects and restore moisture to the toads’ habitat, the World Bank funded construction of the world’s largest gravity-fed artificial mist system.
Unfortunately, nine months passed before the artificial mist system was functional, and the spray zone dried out. In the following years, spurred by additional factors like disease, the toad population plummeted and the species was thought to be extinct in the wild. Before the toads disappeared from the gorge completely, the Tanzanian government invited herpetologists from the Wildlife Conservation Society to collect 500 toads in order to cultivate an insurance population in US zoos, which would guard against total extinction and serve as a source for reintroduction in the future.
Since the conservation effort spanned continents and required the participation of many stakeholder groups, the project’s partners called on CPSG to help them develop a strategy for returning Kihansi spray toads to Tanzania.
In 2007, CPSG led a workshop at which collaborators met to exchange information and define what needed to be done, such as managing disease risks, securing support and partnerships with local communities, and improving understanding of the toads’ unique habitat. Taking these and other challenges into account, they drew a timeline for safely and successfully returning the toads home. The timeline included logistical details, such as acquiring the correct permits to transport captive-bred toads to Tanzania, as well as broader goals, like initiating long-term studies of the Kihansi Gorge. They discussed the construction of a breeding facility for the toads in Dar es Salaam, where Tanzanian biologists would take over the toads’ care before their reintroduction.
“CPSG created the right conditions for identifying the steps to build capacity in Tanzania prior to the toads’ reintroduction,” said Jenny Pramuk, Animal Curator at the Woodland Park Zoo in Seattle, Washington. “When the second workshop took place in 2010, the timelines we created at the first workshop made it clear that many of the tasks had been accomplished, and that the project was on track to move on to the ultimate goal of reintroduction.”
In August 2010, the first “knot” of 100 spray toads from the Bronx and Toledo zoos flew first class to Dar es Salaam. Their arrival was greeted with much media fanfare: the return of the toad to its homeland was a source of celebration and pride for many in Tanzania.
These toads, which were housed in the new breeding facility, became the first in-country colony. In 2012, biologists began releasing captive-bred toads into the Kihansi Gorge, and they continue to closely monitor the species’ progress today.
The wild population was recently estimated to be between 50 and 100 individuals, and the insurance population exceeds 12,000, a remarkable reversal for a species that had been extinct in the wild. Although the wild population is still being augmented with toads from captivity, project partners are another significant step closer to re-establishing Kihansi spray toads in their native habitat.
