Structural Variation in Whistle Patterns of Two Coastal Dolphin Species Co-Occurring in the Southern Israeli Mediterranean Sea

Abstract

Two coastal dolphin species, the common bottlenose dolphin (Tursiops truncatus—Tt) and the short-beaked common dolphin (Delphinus delphis—Dd), co-occur along the southern Israeli Mediterranean coast, where the critically endangered Dd population faces ecological pressures, potentially including competitive exclusion by that of the Tt population. In this context, reliable acoustic differentiation between the two species is needed to supplement visual differentiation. This study aimed to assess whether species-specific whistle characteristics could be used to acoustically distinguish between the two taxa using a novel manual contour extraction tool, Sound Annotator, combined with machine learning classification. A total of 940 high-quality whistles (705 Dd, 235 Tt) from field recordings collected between 2018 and 2024 were available for analysis. Sixteen frequency, temporal, and shape parameters were derived from the extracted contours and analyzed with multiple classification models. Principal component analysis revealed high acoustic overlap, yet the XGBoost classifier effectively classified individual whistles, with minimum, median, and beginning frequency emerging as the most informative features. This framework facilitates non-invasive, species-specific monitoring of dolphin populations in challenging visual conditions, particularly at night, providing a foundation for conservation-focused acoustic monitoring in the eastern Mediterranean.