Baboons in our study area respond differently to different predators. For example, when they encounter lions at close range they escape into trees but when they encounter leopards, at least during daylight hours, they chase and even attack them. When baboons encounter pythons they become vigilant, approach, and give alarms, but when they encounter crocodiles near the river they give choruses of alarm calls and flee from the water's edge. However, despite these different responses, the alarm calls that baboons give to different predators grade acoustically into one another. This observation is significant because it argues against the hypothesis that selection favors the evolution of acoustically distinct calls whenever individuals confront predators with different hunting strategies or social events like inter-group encounters that demand qualitatively different responses.
Females produce at least two alarm call types.
In the double sharp bark the arching harmonic structure is preserved but there is an interruption of energy or break in the middle of the call. This break is very salient, at least to humans. Although sample sizes are small, we have been unable to document any acoustic differences between alarm barks given to crocodiles and snakes. Unlike the sharp bark, the crocodile bark shows little or no harmonic structure and no arch-shaped frequency modulation. The calls shown here represent clear, unambiguous examples of each alarm type.