Rates, Ripples, and Responsivity: The Geometry of Echolocation in Water-Foraging Bats

Water-surface foraging is a rare strategy among echolocating bats, requiring precise coordination between sonar emission, echo timing, and flight geometry. Here, I develop a geometric-responsivity framework to explain how bats foraging over water regulate call timing under these constraints. The model links beam projection, flight height, and specular surface reflections to predictable call-rate scaling and near-field interference patterns. Field recordings of Myotis daubentonii reveal spatially invariant spectral ripples across microphones, confirming a geometric interference origin rather than receiver-dependent effects. Reanalysis of classic data from Noctilio leporinus shows that call rates are inconsistent with continuous prey-distance locking and instead reflect regulation relative to stable surface-related echoes, with prey-centred control emerging only at close range. Together, these results demonstrate that water-foraging bats structure call timing using environmental reference echoes, providing a mechanistic explanation for the acoustic constraints that shape this specialised foraging niche.