BBC News By Victoria Gill media captionListen to the sound of the regent honeyeaters' song A rare songbird has become so threatened that it has started to lose its song, say scientists. The regent honeyeater, once abundant in south-eastern Australia, is now listed as critically endangered; just 300 individuals remain in the world. "They don't get the chance to hang around with other honeyeaters and learn what they're supposed to sound like," explained Dr Ross Crates. 'Needle in a haystack' The researchers had not set out to study the song of the regent honeyeater, but simply to find the birds. "They're so rare and the area they could occupy is so big - probably 10 times the size of the UK - that we were looking for a needle in a haystack," said Dr Crates.