Classification of dolphin echolocation clicks by energy and frequency distributions

Dolphins demonstrate an adaptive control over echolocation click production , but little is known of the manner or degree with which control is exercis ed. Echolocation clicks (N similar to 30 000) were collected from an Atlant ic bottlenose dolphin (Tursiops truncatus) performing object discrimination tasks in order to investigate differential click production. Seven categor ies of clicks were identified using the spectral conformation and relative position of -3 and -10 dB peaks. A counterpropagation network utilizing 16 inputs, 50 hidden units, and 8 output units was trained to classify clicks using the same spectral variables. The network classified novel clicks with 92% success. Additional echolocation clicks (N> 24 000) from two other dol phins were submitted to the network for classification. Classified echoloca tion clicks were analyzed for animal specific differences, changes in predo minant click type within click trains, and task-related specificity. Differ ences in animal and task performance may influence click type and click tra in length. (C) 1999 Acoustical Society of America. [S0001-4966(49)05109-7].