In The Voyage of the Beagle, Charles Darwin and his company explore the Galapagos Islands. The creatures there are not especially used to humans, so they behave in seemingly strange ways. When Darwin is on Chatham Island, he sees two tortoises. One merely looks at him and slowly walks away. The other gives a hiss and puts its head into its shell, rather startled. Yet neither animal appears to be especially frightened, and they are not at all aggressive. The birds, too, Darwin notes, care nothing about him. They don't know that humans can hurt them, so they are not scared.
A bit later in his discussion of the Galapagos, Darwin records that he has observed twenty-six varieties of land birds, the "most singular" of which are finches. He also notes eleven kinds of water birds, three of which are new species to him. Darwin proceeds to describe the birds and their habits in great detail. The fact that he can watch them like he does and see their usual habits suggests that they are not bothered by the humans, for they probably have not seen very many and don't recognize them as potentially dangerous. They merely continue with their bird routines.
A few paragraphs later, Darwin turns his attention to the tortoises again. He describes their appearance and habits, and again, the fact that he can get close enough to observe them so thoroughly suggests that they are not afraid of him. Sometimes the tortoises will pull in their heads and legs at Darwin's approach. Other times, though, he can actually get up on their backs and ride them for a while, even though he finds it difficult to keep his balance.
Finally, with regard to the finches, Darwin notes that a boy in a colonized area of the Galapagos is killing both doves and finches that come to drink at the well. The birds have not developed a fear of humans and therefore, as Darwin says, have not "as yet learnt that man is a more dangerous animal than the tortoise," and therefore they disregard humans just like birds in England pay no attention to cows and horses.