From Temporal Substrate to Multi-Channel Coordination: Acoustic Bandwidth Expansion in Delphinids

Cetacean acoustic behavior exhibits pronounced variability across species, contexts, and signal classes. While often interpreted in semantic or communicative terms, the temporal structure underlying these signals has received less unified treatment. Building on prior work establishing temporal repetition architecture as a substrate invariant across cetaceans, this paper examines how additional acoustic degrees of freedom become registrable under expanded operating modes. Synthesizing evidence on inter-pulse interval scaling, repetition density shifts following perturbation, maneuver-linked timing compression, regime transitions between tonal and pulsed modes, and temporal invariants underlying identity encoding, we show that acoustic variability aligns with predictable constraint-driven retuning. Shallow reverberant habitats narrow admissible update intervals, while increased maneuver bandwidth and proximity contraction drive systematic compression of inter-pulse intervals. Multi-bandwidth species exhibit discrete transitions between cohesion-dominant tonal modes and high-resolution pulsed regimes under range closure, masking, or coordination pressure. This framework does not negate semantic interpretations but demonstrates that temporal stability constraints are sufficient to account for much documented acoustic variation. Delphinid vocal complexity may therefore reflect expanded access to dynamically admissible temporal modes rather than categorical differences in communicative architecture.