The use of manual and bodily gestures to communicate with other conspecifics has been reported for both monkeys and great apes. Gestures are mainly observed in relatively intimate social contexts such as play, grooming, nursing, and during sexual and agonistic encounters which in general represent rather different functions from those signaled by acts of vocal communication (e.g., avoiding predators, defending against aggressors, traveling as a group, discovering food).
Gestures are defined as expressive movements of limbs or head and body postures that are directed toward a recipient, are goal-directed, mechanically ineffective (which means, they are not designed to act as direct physical agents), and receive a voluntary response (Pika 2008a, 2008b).
The following behavioural criteria were used to infer goal-directedness:
Thus, gestures that appear to have components of ritualised morphology (e.g., chest beat) are also included in this definition, if they meet these above mentioned criteria.
The following file is an example of gestures of gorillas (Dierenpark Apenheul, the Netherlands), showing the behavioral criteria response waiting, look at the recipient and repetition of gesture. Example (Right click on the link to save the file, Windows Media, 16Mb)
Animals can also combine gestures and vocalizations which are then termed multimodal signals or combinations.
Vocalizations is a means of communication generated in many cases by vocal cords (e.g. primates), by means of a constant breath of air from the mouth (birds) or made via the blowhole of mammalian species (e.g. cetaceans).