Amphibians
Kihansi Spray Toad
Nectophrynoides asperginis · also called kihansi spray toad
The Kihansi spray toad is a tiny yellow toad that once lived in a single place on Earth: a mist-soaked patch of wetland, about two hectares in size, at the foot of a waterfall in the mountains of Tanzania. When a dam turned off the spray, the toad vanished from the wild within a few years — but not before 500 of them were flown to American zoos, and it has since been bred by the thousand and carried back to the gorge.
Overview
The Kihansi spray toad was endemic to the spray zone of the Kihansi Falls in the Udzungwa Mountains. It is one of the smallest toads, only 1.5–2 cm long, the male yellow and the female olive-brown. It ate springtails, mites, and small flies from the constantly wet moss and leaves, and it gave birth to fully formed toadlets rather than laying eggs — an adaptation to a home with no pools.
The dam
A hydroelectric dam completed around 2000 diverted most of the river above the falls, cutting the spray that kept the wetland alive. An artificial sprinkler system was later built to try to replace it. Soon after the flow changed, the disease chytridiomycosis arrived. Between the drying and the disease, the population collapsed, and the last wild toads were seen in 2004. The IUCN declared the species Extinct in the Wild in 2009.
The rescue
In 2000, about 500 toads were flown to the Bronx and Toledo Zoos. After difficult early years the captive colony bred well and grew into the tens of thousands. From 2012 onward, many thousands of captive-bred toads have been released back at Kihansi.
Status
The species remains listed as Extinct in the Wild. Some released toads have survived and bred in the gorge, but a self-sustaining wild population has not yet been confirmed, and monitoring continues.
Kihansi Spray Toad: common questions
What happened to the Kihansi spray toad in the wild?
Its whole world was a two-hectare wetland kept wet by the spray of the Kihansi Falls. In the late 1990s a hydroelectric dam was built above the falls, and when it began operating around 2000 it diverted roughly 90 percent of the river, so the spray that maintained the toad's habitat largely stopped. The wetland began to dry and change. Soon afterwards the amphibian disease chytridiomycosis reached the site. Between the drying and the disease the population collapsed, and by 2004 no more wild toads could be found. In 2009 the species was formally declared Extinct in the Wild.
How was the species saved from total extinction?
By a rescue mission carried out just before the collapse. In 2000, recognising the threat from the dam, biologists collected about 500 Kihansi spray toads and flew them to the Bronx Zoo and the Toledo Zoo in the United States. Establishing a stable captive population proved difficult at first, with early losses, but the toads eventually bred well, and the captive colony grew into the tens of thousands across several institutions, including facilities in Tanzania. That captive population is the reason the species still exists at all.
Have the reintroduced toads re-established a wild population?
Not yet in a confirmed, self-sustaining way. Starting in 2012, tens of thousands of captive-bred toads have been released into the Kihansi gorge, where an artificial sprinkler system now mimics some of the lost spray and where efforts have been made to manage the chytrid fungus. Some released toads have survived and bred at the site, which is encouraging, but conservationists have been cautious about declaring the wild population restored, because it is not clear the toads can persist there without continued support. The species remains listed as Extinct in the Wild while monitoring continues.
Why did such a tiny, localised species matter enough to rescue?
The Kihansi spray toad is a clear example of what is at stake when a single specialised habitat is altered, and of the fact that extinction in the wild is not always the end. It also has scientific interest as one of the few toads that give live birth rather than laying eggs, an adaptation to a home with no pools. And the rescue and captive-breeding effort, run jointly by Tanzanian authorities and American zoos, has served as a model, and a cautionary tale, for how large infrastructure projects can be paired with attempts to save the species they threaten.