Individual variation in the relationship between vigilance and group size in eastern grey kangaroos

摘要: The mean vigilance of animals in a group often decreases as their size increases, yet nothing is known about whether there individual variability this relationship species that change sizes frequently, such those exhibit fission-fusion social systems. We investigated the between and eastern grey kangaroo (Macropus giganteus) by testing all individuals showed decreased with increased size, has been commonly assumed. carried out both behavioural observations entire groups kangaroos focal individually recognised wild female kangaroos. As other studies, we found collective group-size effect on vigilance; however, varied patterns. majority (57%) identified did not show significant effects for any recorded measures vigilance. females negative were, average, more vigilant than effect, but difference was significant. propose some higher levels others, increases cancelling anti-predator females. Our results therefore suggest only prey may gain benefits reducing time spent scanning when larger groups. large amount variation behaviour highlights importance collecting analysing data at level, which requires recognition.