the expedition had taken more care. He now sought specimens collected by captain Robert FitzRoy and crewmen. From them he was able to establish that the species were unique to islands, an important step on the inception of his theory of evolution by natural selection. Gould's work on the birds was published between 1838 and 1842 in five numbers as Part 3 of Zoology of the Voyage of H.M.S. Beagle,