Marabou stork of any landbird, to rival the Andean condor; more typically, however, these storks measure across the wings, which is about a foot less than the average Andean condor wingspan and nearly two feet less than the average of the largest albatrosses and pelicans. Typical weight is , unusually as low as , and length (from bill to tail) is . Females are smaller than males. Bill length can range from . Unlike most storks, the three "Leptoptilos" species fly with the neck retracted like a heron. The marabou is unmistakable due to its size, bare head and neck, black back,
What Bird is That? according to their usual habitat. The accompanying text included brief notes on distribution, breeding and behaviour. While initial sales were poor, history tells us that Cayley had accurately discerned a market need and successfully responded to it. During WWII sales accelerated and Cayley’s first collection, reprinted time and time again, eventually became a household name among birdwatchers and the book was recognised as an Australian classic. The original sponsorship of "What Bird is That?" proved a great investment for the Gould League, who benefited from the sale of its numerous reprints and revised editions. By 1960, it was rated the