Each indri is a phase oscillator θᵢ that "calls" whenever its phase crosses 0. Neighbors within an acoustic radius R pull each other's phase together — the classic Kuramoto coupled-oscillator model used to describe synchronized chorusing, firefly flashing and neuron firing:
dθᵢ/dt = ωᵢ + (K / nᵢ) · Σⱼ sin(θⱼ − θᵢ) for j within R
ωᵢ is each animal's own natural call rate (spread by the "call-rate diversity" slider), K is coupling strength, and nᵢ is its neighbor count. R shrinks as "territorial spacing" grows, modeling how spread-out groups hear fewer neighbors and stay less synchronized.
- Synchrony (r) — the Kuramoto order parameter, r·e^(iψ) = (1/N)Σₖ e^(iθₖ); r = 1 means every indri calls in perfect unison, r ≈ 0 means phases are scattered.
- Canopy glow — each indri's ring brightens as its phase nears 0 (the call moment); lines between neighbors brighten when their phases align.