Story highlights Sumatran rhino seen last month for the first time in 40 years

Now conservationists say the female rhino has died

(CNN) The optimistic story of a Sumatran rhino took a dark turn when the mammal died weeks after a rare sighting.

The female Sumatran rhino was caught in a pit trap last month -- the first time in 40 years the species was seen in Kalimantan, the Indonesia part of Borneo.

Now conservationists say the female rhino has died after raising hopes the species still roams the forests. Sumatran rhinos are one of two rhino species in Indonesia.

Conservationists cheered the rhino's rediscovery, only to mourn the animal weeks later. It was unclear what killed the animal.

"Our hearts are saddened by this devastating news from Kalimantan," the International Rhino Foundation said in a statement Tuesday.

Read More