Northern rockhopper penguin truly different, in terms of more than reproductive isolation and some morphological features, was found in the mitochondrial sequences of the three species. It was found "E. c. filholi" and "E. c. chrysocome" were not as different genetically as "E. c. moseleyi" was to the other two subspecies. The level of genetic differentiation was similar to the genetic difference found in other penguin subspecies groups. Another way that scientists were able to differentiate the different subspecies of rockhoppers were in the parasites that fed off each separate rockhopper penguin species. Penguins are parasitised by 15 species of chewing lice in
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