(CNN)When humans first began settling in the Galapagos Islands nearly two centuries ago, they brought house cats.
Those cats hunted finches, scaring the small birds who were unused to the predator. A decade ago, the cat population was largely removed but the finches still act as if they are in danger, puzzling scientists.
"It suggests the behavior could be hereditary, but it could also be other things such as learning or cultural transmission of behavior," said Kiyoko Gotanda, a zoologist at the University of Cambridge.
The finches' fearful responses, which scientists call anti-predator behavior, now pose a threat to their survival, according to a Gotanda's study, which was published Wednesday in the Journal of Animal Ecology.
Humans settled on the Galapagos archipelago, famed for its rich biodiversity that inspired Charles Darwin's theory of evolution, in the early 19th century. Apart from cats, settlers also introduced invasive species like rats, dogs, and pigs -- which spelled trouble for small native island animals.
These animals, including birds and reptiles, displayed little anti-predator behavior back then because they had never seen these new predators before -- they were only used to local predators like owls.
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