title: Transmission beam characteristics of a Risso's dolphin (Grampus griseus).
abstract: The echolocation system of the Risso's dolphin (Grampus griseus) remains poorly studied compared to other odontocete species. In this study, echolocation signals were recorded from a stationary Risso's dolphin with an array of 16 hydrophones and the two-dimensional beam shape was explored using frequency-dependent amplitude plots. Click source parameters were similar to those already described for this species. Centroid frequency of click signals increased with increasing sound pressure level, while the beamwidth decreased with increasing center frequency. Analysis revealed primarily single-lobed, and occasionally vertically dual-lobed, beam shapes. Overall beam directivity was found to be greater than that of the harbor porpoise, bottlenose dolphin, and a false killer whale. The relationship between frequency content, beam directivity, and head size for this Risso's dolphin deviated from the trend described for other species. These are the first reported measurements of echolocation beam shape and directivity in G. griseus.
authors.affiliation: Marine Mammal Research Program, Hawaii Institute of Marine Biology, University of Hawaii at Manoa, Kaneohe, Hawaii 96744, USA.
authors.forename: Adam B
authors.initials: AB
authors.lastname: Smith
authors.affiliation: Department of Biology, Saint Mary's College, Notre Dame, Indiana 46556, USA.
authors.forename: Laura N
authors.initials: LN
authors.lastname: Kloepper
authors.affiliation: Department of Veterinary Medicine, National Chiayi University, Chiayi City, Taiwan.
authors.forename: Wei-Cheng
authors.initials: WC
authors.lastname: Yang
authors.affiliation: Farglory Ocean Park, Hualien County, Taiwan.
authors.forename: Wan-Hsiu
authors.initials: WH
authors.lastname: Huang
authors.affiliation: Farglory Ocean Park, Hualien County, Taiwan.
authors.forename: I-Fan
authors.initials: IF
authors.lastname: Jen
authors.affiliation: Department of Ocean and Resources Engineering, University of Hawaii at Manoa, Honolulu, Hawaii 96822, USA.
authors.forename: Brendan P
authors.initials: BP
authors.lastname: Rideout
authors.affiliation: Marine Mammal Research Program, Hawaii Institute of Marine Biology, University of Hawaii at Manoa, Kaneohe, Hawaii 96744, USA.
authors.forename: Paul E
authors.initials: PE
authors.lastname: Nachtigall
mesh_terms: D000818:Animals; D004289:Dolphins / Q000502:physiology*; D004455:Echolocation / Q000502:physiology*; D005260:Female; D006257:Head / Q000033:anatomy & histology; D012044:Regression Analysis; D013018:Sound Spectrography