Herring gulls notice where approaching humans are looking, and flee sooner when they're being watched, a new study shows.
Researchers approached gulls while either looking at the ground or directly at the birds.
Gulls were slower to move away when not being watched - allowing a human to get two metres closer on average.
Newly fledged gulls were just as likely to react to human gaze direction as older birds, suggesting they are born with this tendency or quickly learn it.
The study, by the University of Exeter, also confirms the widely held view that urban gulls are bolder than rural gulls - letting a person get on average 2.5m closer before walking or flying away.
"Herring gulls are increasingly breeding and foraging in urban areas, and therefore have regular interactions with humans," said lead author Madeleine Goumas, of the Centre for Ecology and Conservation at Exeter's Penryn Campus in Cornwall.
"We know from previous research that gulls are less likely to peck a bag of chips if a human is watching - but in that experiment the researcher either looked at the gulls or turned their head away.
"In our new study, the experimenter approached while facing the gull and only changed the direction of their eyes - either looking down or at the gull.
"We were interested to find that gulls pay attention to human eye direction specifically, and that this is true for juveniles as well as adults - so their aversion to human gaze isn't a result of months or years of negative interactions with people."
The study was conducted in Cornwall, UK, targeting adult gulls (aged four years or older, evidenced by white and grey plumage) and juveniles (born in the year of the study, with completely brown plumage).
A total of 155 gulls were included in the findings: 50 adults and 45 juveniles in urban settlements, and 34 adults and 26 juveniles in rural settlements.
As well as being quicker to flee, rural gulls were also more than three times as likely to fly - rather than walk - away from an approaching human, suggesting they are less used to being approached.
"The growing number of herring gulls in urban areas may make them appear more common than they really are," Goumas said.
"The species is actually in decline in the UK, and we hope our ongoing research into human-gull interactions will contribute to conservation efforts."
The paper, published in the journal Animal Behaviour, is entitled: "Herring gull aversion to gaze in urban and rural human settlements."