Media playback is unsupported on your device Media caption The world's rarest bird is on brink of extinction, as Victoria Gill reports

The Madagascar pochard, the world's rarest bird, will not be able to thrive without a new wetland home.

This is according to a study revealing that 96% of the chicks are dying at two to three weeks old.

Conservationists say that human activity has driven the birds to one remaining wetland, but that that site has insufficient food for the ducks.

The research is published in the journal Bird Conservation International.

Image copyright WWT Image caption The wetland where the ducks survive is relatively pristine but too deep for young ducklings to dive for food

The Wildfowl and Wetlands Trust (WWT), which led the research, estimates that only 25 individual birds now remain in the wild.

Human activity, including deforestation, farming and fishing, has destroyed their habitat to the point that this last population is now restricted to one wetland in north-east Madagascar - a complex of lakes near Bemanevika.

After the rediscovery of the species at this site in 2006, the WWT and its partners, including the Durrell Wildlife Conservation Trust and the Peregrine Fund, set up a conservation breeding programme and began to monitor the wild birds.

Dr Geoff Hilton, head of species research at the WWT, said that with such a small number of birds, keeping a close eye on the population was straightforward.

"We had about 10 or 11 females, [and] we were able to tell that most of those females were laying eggs, and those eggs were hatching," he told BBC News.

But at the point when the ducklings were two to three weeks old, they would start disappearing.

Too deep to dive

Piecing the evidence together, including samples of food from the bottom of the lake, the researchers realised that the chicks were starving to death.

Image copyright WWT Image caption Local and international conservationists are working together to find a new home for the rare ducks

These diving ducks feed from the bottom of lakes, and this steep crater lake was simply too deep for them.

WWT senior research officer Dr Andrew Bamford, who led the study, said: "The last refuge of the Madagascar pochard is one of the last unspoilt wetlands in the country, but it's simply not suited to its needs.

"Something similar happened in the UK when the lowland red kite became confined to upland Wales, and in Hawaii, where the last nenes survived only on the upper slopes of volcanoes because introduced predators had occupied their favoured grassland habitats."

Dr Hilton added: "What we think we're seeing is a bit of a classic wildlife conservation conundrum.

"The place where the species hangs on at the end is not a particularly good place for them - it's just the place that's been least badly affected by human activities."

Media playback is unsupported on your device Media caption Peter Cranswick of the Wildfowl and Wetlands Trust explains the risks faced by the Madagascar pochard

But the researchers say the species could thrive in Madagascar again if the captive-bred ducks can be found a new wetland home.

"We have been very successful in establishing a captive population," said Dr Hilton.

"And we have recently identified a lake that we think has potential to be restored and become a reintroduction site.

"The main thing we have to do is work with the local people to reintroduce and restore the pochard, but also to restore the lake and help people to get a better livelihood from the lake they live around."

Image copyright WWT Image caption The researchers have had great success with a captive breeding programme for the pochard

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