Okay, let's try this again -

drongo
A fool, a simpleton, an idiot. There is also a bird called a drongo. The spangled drongo is found in northern and eastern Australia, as well as in the islands to the north of Australia, and further north to India and China. It is called a drongo because that is the name of a bird from the same family in northern Madagascar. The spangled drongo is not a stupid bird. It is not a galah. One book describes it thus: 'The spangled drongo catches insects in the air, chasing them in aerobatic flight'. There is one odd story about the drongo, however: unlike most migratory birds, it appears to migrate to colder regions in winter. Some have suggested that this is the origin of the association of 'stupidity' with the term drongo. But this seems most unlikely.
So what is the true story? There was an Australian racehorse called Drongo during the early 1920s. It seems likely that he was named after the bird called the 'drongo'. He wasn't a an absolute no-hoper of a racehorse: he ran second in a VRC Derby and St Leger, third in the AJC St Leger, and fifth in the 1924 Sydney Cup. He often came very close to winning major races, but in 37 starts he never won a race. In 1924 a writer in the Melbourne Argus comments: 'Drongo is sure to be a very hard horse to beat. He is improving with every run'. But he never did win.
Soon after the horse's retirement it seems that racegoers started to apply the term to horses that were having similarly unlucky careers. Soon after the term became more negative, and was applied also to people who were not so much 'unlucky' as 'hopeless cases', 'no-hopers', and thereafter 'fools'. In the 1940s it was applied to recruits in the Royal Australian Air Force. It has become part of general Australian slang.
Buzz Kennedy, writing in The Australian newspaper in 1977, defines a drongo thus: