Indri

Indris produce loud, haunting songs that can be heard over 2 kilometers. Unlike gibbon duets between pairs, indri songs are group choruses—all family members join in coordinated singing. This group singing may advertise group size and coordination to neighbors, deterring territorial intrusion more effectively than individual calls could.

Group size is encoded in chorus complexity. Larger groups produce richer, more complex choruses with more overlapping parts. Listeners can potentially estimate group size from chorus acoustic properties. This information could deter small groups from challenging large ones.

Song timing is contagious. When one group begins singing, neighboring groups often join within minutes, creating 'singing bouts' where multiple groups chorus across the forest. This contagious singing may help establish territorial boundaries through acoustic interaction without physical confrontation.

The songs have cultural components. Different populations have distinct song structures—'dialects' that persist across generations. Young indris learn their group's song variant through exposure, creating cultural traditions that identify group membership.

For organizations, indris illustrate that coordinated group signals amplify individual contributions. Team presentations, coordinated announcements, and synchronized responses demonstrate group cohesion that individual communications cannot match.