A puppet is used along with a special suit worn by staff to disguise them.David Waters, from the GBG, told the BBC that if it was a “reasonable year” it would be the first “new great bustard population” to be established “anywhere in the world”. Standing up to 3ft tall and with a wingspan of more than 8ft, some Great Bustards have been known to weigh as much as 21kg (46lb) Adult male bustards can be identified by their bulging neckCredit:AFP/Getty Images Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings. David Waters reveals the birds have started to breed Credit:Justin Sutcliffe He said: “The birds have started to breed. We had six nests last year and we’ll have a theoretical maximum this year of 21 nests.” Mr Waters added that once the Wiltshire birds were “self-sustaining” the group would “stop bringing birds in” from Russia and Spain.Huge and heavily built, adult male bustards can be identified by their bulging neck, heavy chest and cocked tail. Great Bustards, which were hunted into extinction in 1832, are now “on the point” of become self-sustainable, thanks to a pioneering scheme which has reintroduced the species to the UK.Once a familiar sight in grassland areas of southern Britain, the world’s heaviest bird suffered a dramatic decline in the early 19th Century because its size made it an easy target for hunters.But since 2004, hundreds of chicks have been released by charity the Great Bustard Group (GBG) on Salisbury Plain in Wiltshire and a strong breeding population has been established. The project has established a breeding population of Great Bustards, which had been extinct since the middle of the 19th Century.— Clarence House (@ClarenceHouse) March 17, 2017 The birds can have a wingspan of more than 8ftCredit:PA The Prince visited the Great Bustard Project in Wiltshire today to hear about their work helping to conserve endangered Great Bustard birds. pic.twitter.com/nV21eIvuiS— Clarence House (@ClarenceHouse) March 17, 2017 The birds are omnivorous and their diet is mainly composed of plants, berries, insects and sometimes voles and lizards.It is hoped that by 2019 the number of “release birds” will have reached 100. On Friday, The Prince of Wales visited the project and was told how the population had grown from 10 birds to at least 48 in less than three years.Project staff, who are almost entirely volunteers, described the rearing process as “complex” as the young chicks need to be bill fed.