•Explicate surrogacy of acoustic indices for rapid assessment of avian diversity.•Compares pre and post flood avian diversity using acoustic indices.•Acoustic estimation of biodiversity act as a travellator to realize conservation goals. Biodiversity assessment, in the aftermath of a natural disaster, remains a challenge. Sonic (acoustic) analysis is increasingly gaining acceptance as a means of rapid assessment of biodiversity. However, its utility in the immediate aftermath of natural disasters is unreported. We compare pre-flood, flood-period and post-flood acoustic indices of Salim Ali Bird Sanctuary, Kerala, India, to illustrate their utility in assessing avian biodiversity. The temporal dynamics of acoustic indices capture the spectre of floods on avian diversity and its resurgence with time in the sanctuary. Display omitted