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After being kept in captivity and isolated from natural predators for more than 1200 years,Pere Davids deer has been reintroduced in China and now occurs m a reserve where human activity is the only potential threat.Antipredator vigilance is an important component of survival for many prey animals in their natural habitat.Do deer still adjust vigilance as a function of risk after such a long period of relaxed predation pressure? Here,we examined vigilance levels in Pere Davids deer groups as a function of group size,sex and level of human disturbance.The results showed that individual vigilance significantly decreased with group size in all-female groups but not in all-males or mixed-sex groups.In rutting season,males compete with one another and harass females,and we argue that vigilance is partly aimed at threatening males and that such vigilance increases with group size.This explains why overall vigilance did not vary with group size for males in general and for females in mixed-sex groups.Vigilance increased in more disturbed areas but in in male deer only.The results indicate that despite relaxed predation pressure over centuries,Pere Davids deer can still adjust antipredator responses as a function of perceived risk.Such information may become useful in the rewildingprogramme now under way for this species in China.