Costa Rican scientists have reported the reappearance of an endemic frog species that was declared extinct by the International Union for Conservation of Nature (UICN) in the year 2004.

The scientists on Tuesday reported sighting of the frog species that had not been seen for three decades, Efe news reported.

The Heredia robber frog, whose scientific name is Craugastor escoces, was spotted by Costa Rican biologists Gilbert Alvarado and Randall Jimenez in the Juan Castro Blanco National Park in Alajuela.

"From Mexico to Panama, there are 34 species of this kind (Craugastor). In Costa Rica, there are eight of them and in the 1990s, all of those living above an altitude of 1,000 metres disappeared," Alvarado said.

"Nothing more was known about them. The Heredia robber frog was declared extinct in 2004 but now we're going to bring it back," Alvarado said at a press conference.

The discovery occurred on September 19, 2016, while collecting a sample of amphibians.

The frog that was found was a coffee-coloured adult female with a red belly and measures 6.2 cm. This species had not been observed since 1986.

In 2004, the UICN declared three amphibians extinct: This robber frog, the Holdridge's toad (also known as the deaf-and-dumb toad), and the golden toad.

The only one still on the extinct list is the golden toad, which researchers consider the first victim of global warming.

For Alvarado, losing a species is a "hard blow for science and for biodiversity, because they represent years of evolution and each one has a biological function within the ecosystem".

"Knowing that the robber frog is there means recovering genetic material of incalculable value," the biologist said.

The discovery occurred in a ravine at an altitude of 1,820 metres, which makes researchers think there must be a robber frog population surviving there.

Little is known about the species.

Official data indicate that in this Central American country there are more than 200 species of frogs and toads.

Costa Rica, with 4.7 million inhabitants, has close to 4.5 per cent of the biodiversity on the planet, and is one of the top 20 nations in terms of biodiversity.

Source: June 7, 2017, The Times of India