Crows can learn to recognize familiar human voices and the calls of familiar birds from other species, Austrian researchers say. Scientists at the University of Vienna say the findings suggest the ability could help crows thrive in urban environments, using vocal cues from human and bird neighbors to find food or be alerted to potential threats. \"In cities crows live alongside jackdaws, magpies and seagulls, and alongside humans,\" researcher Claudia Wascher told the BBC. \"Some of those people might be very nice to the crows and feed them and others might be nasty and chase them away.\" The scientists used recordings of human voices and jackdaw calls to test the responses of eight crows in the university\'s aviary. They recorded the voices of five people who feed the crows every day and five others who \"had never met the crows,\" Wascher said. When the recordings were played to the birds, they responded much more when they heard the unfamiliar voices, looking up and turning toward the sound. \"Since humans can be a serious threat for crows,\" Wascher said, \"it\'s important that if they hear someone unfamiliar, they are on alert.\" Although it was widely known that crows are \"very intelligent,\" she said, most studies have focused on their ability to recognize and communicate with their own species.