Vets have begun examining the huge body of Bobby the silverback gorilla, the star attraction of London Zoo, to find out why he died suddenly yesterday, at the age of only 25.Even if he had been living.

In the African jungles as his ancestors did, 25 years would have been a short life for a healthy male gorilla. In the wild, they are expected to live for 35 years or more, and in captivity average life expectancy is 50 years.

He was found dead in his nest by keepers early yesterday morning. "Staff, volunteers, members and the general public are devastated by the loss of our gentle giant," Ralph Armond, director general of the Zoological Society of London said."Bobby was a much-loved member of the ZSL family and leaves behind his family of keepers and three female gorillas, Mjukuu, nine, Effie, 15, and Zaire, 34." 

Staff at the zoo were not able to say why Bobby died. One strong probability is he died of cardiomyopathy, a degenerative heart condition to which adult male western lowland gorillas are particularly prone.In 2004, vets successfully implanted a pacemaker in a 24-year-old silverback named Babec.

At the Birmingham Zoo in Alabama, who survived until April this year, despite dislodging the pacemaker once while wrestling with another gorilla. But when veterinarians attempted a similar implant two years ago on a 23-year-old named Kuja in Washington's National Zoo, he died during the operation.

Bobby's death is a financial blow to London Zoo, which invested £5.3m in its new Gorilla Kingdom enclosure, which was officially opened by the Duke of Edinburgh in March 2007. The attraction, billed as "the zoo's most significant investment for more than 40 years", has attracted thousands of visitors.

Bongo Junior, to give Bobby his full name, was brought to London from Bristol Zoo in 2003, and was arguably the zoo's greatest attraction. His face was known around the world because of the thousands of posters on which he featured.

Western lowland gorillas are on the "red list" of endangered species, despite having no natural enemies except humans. Until recently, it was feared that their population in the wild had dwindled to less than 50,000, because of poaching and diseases caught from humans.

But the results of a new census earlier this year by the Wildlife Conservation Society suggested that there could be as many as 125,000 living in a remote forest area in the Republic of Congo. Gorillas make a new nest every night before going to sleep.

Despite this survey, which raised hopes for the gorillas' long-term survival in the wild, breeding western lowland gorillas in captivity is still considered an important contribution to preserving the species.In the wild, they are strict vegetarians, living off fruit and tree bark.

The only meat eaters among them are in zoos. They are not aggressive and, even when provoked, the worst they are likely to do is charge at their tormentor. London Zoo will be having a remembrance for Bobby on Wednesday at 3pm, when visitors and staff can pay their respects to the gorilla by laying a wreath in the zoo's courtyard.