Acoustic adaptation in pygmy marmoset contact calls: Locational cues vary with distances between conspecifics

Summary

• 1. The pygmy marmoset, Cebuella pygmaea, has four trill variants in its vocal repertoire. One of these trills has a different behavioral message from the other three. However, the remaining trills, which were physically different from each other, did not seem to differ in their behavioral messages.

• 2. The three trills can be ordered according to their acoustic cues for sound localization. This suggested that the most localizable trill is used when caller and recipient are far apart, while the least localizable trill is used only when animals are close together.

• 3. A field study in the Peruvian Amozon showed that this was correct. Thus, pygmy marmosets seem to use selectively the variations in trill structure to minimize locatability when other cues are available for determining location and to maximize locatability when other means of determining location are absent.

• 4. Pygmy marmoset trills contain mostly high frequency components which decay rapidly over short distances in humid, forested environments. However, these high frequencies are shown to be above the major frequencies of ambient noise in the environment, thus giving the pygmy marmoset a frequency window for communication. Furthermore, the frequencies of the marmoset trills are above the maximum auditory sensitivity of their major predators.