The hearing and echolocation clicks of a stranded Indo-Pacific humpback dolphin (Sousa chinensis) in Zhuhai, China, were studied. This animal had been repeatedly observed in the wild before it was stranded and its age was estimated to be ~40 years. The animal's hearing was measured using a non-invasive auditory evoked potential (AEP) method. Echolocation clicks produced by the dolphin were recorded when the animal was freely swimming in a 7.5 m (width)×22 m (length)×4.8 m (structural depth) pool with a water depth of ~2.5 m. The hearing and echolocation clicks of the studied dolphin were compared with those of a conspecific younger individual, ~13 years of age. The results suggested that the cut-off frequency of the high-frequency hearing of the studied dolphin was ~30–40 kHz lower than that of the younger individual. The peak and centre frequencies of the clicks produced by the older dolphin were ~16 kHz lower than those of the clicks produced by the younger animal. Considering that the older dolphin was ~40 years old, its lower high-frequency hearing range with lower click peak and centre frequencies could probably be explained by age-related hearing loss (presbycusis).
S.L., D.W., K.W., M.H.K., N.F., W.L., J.C. and T.N. designed the study. S.L. analysed the data and interpreted the findings. All authors contributed to the writing and revising of the paper.
No competing interests declared.
The study was supported by the Ocean Park Conservation Foundation, Hong Kong (OPCFHK), National Natural Science Foundation of China [grant nos 31070347, 31170501], Ministry of Science and Technology of China [grant no. 2011BAG07B05-3], State Oceanic Administration of China [grant no. 201105011-3], ‘Hundred Talents Program’ of the Chinese Academy of Sciences [grant no. SIDSSE-BR-201201], Knowledge Innovation Program of the Chinese Academy of Sciences [grant no. SIDSSE-201210], and the Marine Mammal Research Laboratory, Tropical Marine Science Institute, National University of Singapore.
LIST OF ABBREVIATIONS
- A/D converter
- analog-to-digital converter
- auditory evoked potential
- data acquisition card
- envelope-following response
- fast Fourier transform
- root mean square
- sound pressure level
- © 2013. Published by The Company of Biologists Ltd