One of the world’s rarest birds has been sighted for the first time in almost four decades.

An ornithological search-team has caught a glimpse of the Critically Endangered Zapata Rail Cyanolimnas cerverai, one of the world’s most threatened waterbirds.

The bird was sighted at the Zapata Swamp in south-west Cuba, the location which gives the bird its name.

Fewer than 400 individual Zapata Rails are estimated to exist.

Island rails, often poor fliers, are vulnerable to predators and habitat destruction, and 15 species have become extinct since the 17th Century.

The fleeting encounter occurred in November 2014, but has only now been made public by BirdLife International.

A group of ornithologists spotted the bird while surveying the swamp, having cut thin temporary strips, known as rides, into the vegetation in the hope it might lead to a sighting.

“In the first instance, the head protruded from the sawgrass at the side of the ride,” says ornithologist Andy Mitchell, who spotted the bird alongside colleagues from the Cuban Museum of Natural History.

“After a few seconds the bird emerged slowly into the open, stopped for a few seconds before moving off into the sawgrass on the other side of the ride.”

Few images of the bird exist, and hopes were fading that viable populations of the Cuban waterbird remained.

First described in the early twentieth century, only one nest  has ever been found - and little has since been discovered about the bird's behaviour and breeding ecology.

But the new sighting is encouraging, and conservation efforts will now target the wetland in which the rail was spotted, says Birdlife International.