It is generally assumed that alarm calls function in intraspecific communic
ation, for example to warn close relatives about tbe presence of a predator
. However, an alternative hypothesis suggests that, in some cases, signalle
rs may also gain fitness benefits in directly communicating to the predator
, for example by advertising perception and unprofitability to predators th
at depend on unprepared prey. In this study, we show that six monkey specie
s in Tai forest, Ivory Coast, produce significantly more alarm calls to leo
pards than to chimpanzees, although both are notorious monkey predators. Th
e conspicuously high vocalization rates to leopards had adaptive consequenc
es for the monkeys. By following a radio-collared leopard, we found that af
ter detection and high alarm call rates the leopard gave up its hiding loca
tion and left the group significantly faster than would be expected by chan
ce. We discuss these data with respect to the various functional hypothesis
of alarm call behaviour and conclude that the high alarm call rates to leo
pards are part of an anti-predator strategy in primates that may have evolv
ed to deter predators that depend on surprise.