Seoul: While it is only natural for birds living among people to learn to differentiate individual humans, researchers have found that skuas living in remote Antarctica too can recognise people who had previously accessed the nests to measure their eggs and nestlings. The findings suggest that these birds have very high levels of cognitive abilities. "I had to defend myself against the skuas' attack," said one of the researchers Yeong-Deok Han from Inha University in Incheon, South Korea. "When I was with other researchers, the birds flew over me and tried to hit me. Even when I changed my field clothes, they followed me. The birds seemed to know me no matter what I wear," Han noted. The research team performed a series of experiments. The researchers checked the nests once a week to monitor the breeding status, and the skuas attacked at closer distances with repeated visits of the researchers. To test if the birds specifically distinguish the researchers who visited the nests from those who did not, a pair of humans consisting of nest intruder (who accessed the nests) and neutral human (who never accessed the nests before) approached to the nests and walked towards the opposite directions. All seven skua pairs followed and tried to attack the nest intruder but never followed the neutral human. These findings were published in the journal Animal Cognition. "It is amazing that brown skuas, which evolved and lived in human-free habitats, recognised individual humans just after three or four visits. It seems that they have very high levels of cognitive abilities," lead researcher Won Young Lee, senior researcher from Korea Polar Research Institute, said.