Effect of predation risk on grouping pattern and whistling behaviour in a wild mouflon population

We studied the effect of predation risk on grouping pattern and whistling behaviour in a free-ranging mouflon Ovis aries Linnaeus, 1758 population in Sardinia. Direct observations were carried out from July 2005 to June 2007 (n(groups) = 881, n(mouflon) = 3477). In our study site, the rut occurred in October and November, when social sexual segregation disappeared, while lambing peaked in April. Groups with lambs (mean +/- SE: female groups with lambs 4.98 +/- 0.23, mixed groups 6.49 +/- 0.29) were larger than male groups (2.01 +/- 0.10) and female groups without lambs (2.77 +/- 0.11), especially during the lambing season. This reflected the anti-predator tactics adopted by mothers so as to benefit from the dilution effect. Also male aggregations increased in size during the lambing season, as a consequence of the gradual decrease of rutting activities and consequently of male-male aggressiveness. Among the anti-predator tactics adopted by mouflon, whistling behaviour seemed to be a warning signal directed to predators and not to conspecifics. This was because whistling was shown by smaller aggregations only, regardless of group type, presence of lamb and habitat occupied. Smaller groups cannot profit from the dilution effect and therefore may be more motivated to signal the predator that it has been spotted.