Target detection: Beluga whale and bottlenose dolphin echolocation abilities compared

Abstract

An experiment compared the echolocation abilities of a beluga whale and a bottlenose dolphin to detect five targets of the same size and target strength ( + / − 2 dB) at distances from 40 to 120 m. The performance for both animals at 40, 60, 80, and 100 m exceeded 90% correct detection; however, performance at 120 m ranged between 60% to 62% correct detection. The beluga whale and the bottlenose dolphin were tested with the same targets at 5‐m increments at distances from 100 to 120 m. These test results indicated: (1) no significantly different performance (p < 0.05) between the beluga whale and bottlenose dolphin at the five test distances, (2) both animals differentially reported three of the five targets, independent of target distance, and (3) the performance of both animals at 120 m ranged between 60% to 90% correct detection depending on which target was presented at 120 m. There may be several reasons why both animals differentially reported three of the targets at ranges beyond 100 m, irrespective of absolute distance: (1) variable target strength, (2) the manner in which the targets were suspended plus rotational motion about the suspension point may have induced target echo variability, and (3) for targets under 100 m, target echo levels were large and both the beluga whale and bottlenose dolphin were able to differentiate the signal from the background noise. Beyond 100 m, subtle features of the targets determined their detectibility. On two targets, the salient features were apparently unavailable at ranges beyond 100 m, and differential detection occurred. Because the range differences were small, the significant target feature that was absent was not solely a function of spherical spreading loss.