Researchers tracking a single population of crows in one city park found that the birds could distinguish among individual human faces, cawing in alarm at people who had once disturbed their nests while ignoring strangers who passed nearby. The effect persisted for months. The authors caution that they observed only one flock and cannot say whether crows elsewhere share the ability; they present the work as a first, local demonstration, not a settled fact about the species.
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Which choice best states the main idea of the text?
ACrows are among the most intelligent birds in the world.
BOne studied flock of crows could recognize particular human faces, though the researchers stop short of generalizing to all crows.
CCrows everywhere can remember and react to the specific humans who threaten their nests.
DCrows caw in alarm whenever a human approaches their nests.