Southern rockhopper penguin penguins which get around obstacles by sliding on their bellies or by awkward climbing using their flipper-like wings as aid, rockhoppers will try to jump over boulders and across cracks. This behaviour is by no means unique to this species however - at least the other "crested" penguins of the genus "Eudyptes" hop around rocks too. But the rockhopper's congeners occur on remote islands in the New Zealand region, whereas the rockhopper penguins are found in places that were visited by explorers and whalers since the Early Modern era. Hence, it is this particular species in which this behaviour was
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