3
In Search of Impulse Sound Sources
in Odontocetes
TED w. CRANFORD
1. Introduction
Naturalists have been aware of the sounds produced by toothed whales,
odontocetes, since the time of the ancient Greeks. The first recordings of
odontocete sounds were published in 1949, when Schevill and Lawrence
used a Dictaphone machine to record sounds from the white whale, Delphinapterus leucas. These "sea canaries" generated a rich variety of sounds
that were reproduced on two phonograph records (Schevill and Lawrence
1950; Schevill and Watkins 1962). The recordings sparked the curiosity of
investigators, who raised questions about the source and function of these
sounds. Since that time, researchers have engaged in attempts to determine
the exact mechanism and specific location for the production of odontocete
echolocation pulses, as well as their formation into a forward-projecting
sonar beam.
This chapter is a chronologic look at the quest to understand biosonar
signal generation, with an emphasis on how the accumulation of evidence
affected interpretation and speculation in the scientific debate. In many
ways, the fervor that arose over the earliest form-function questions in
odontocete echolocation was born from an overly simplistic view of the
degree to which aquatic adaptation could revamp and refine a sensory
system. Professor Norris (1964) cautioned us against such underestimation
in a passage that is apt today:
One fact has consistently emerged from recent biological studies, particularly in the
spheres of biophysics and anatomy, and it is that we humans have, in the past, usually
underestimated the refinements of animal adaptations. Accordingly, if we are to
establish a working hypothesis for cetacean echolocation and its anatomical correlates, it is probably better to expect sophistication and to attribute function to structure, than it is to be forced eventually to such a viewpoint from the more sparse
interpretation that structures, even complex ones, need not have a function. (Norris
1964,p.324)
Before we frame the historical perspectives of the scientific debate and
address the issues that currently surround the questions that remain, let me
109
In Search of Impulse Sound Sources
in Odontocetes
TED w. CRANFORD
1. Introduction
Naturalists have been aware of the sounds produced by toothed whales,
odontocetes, since the time of the ancient Greeks. The first recordings of
odontocete sounds were published in 1949, when Schevill and Lawrence
used a Dictaphone machine to record sounds from the white whale, Delphinapterus leucas. These "sea canaries" generated a rich variety of sounds
that were reproduced on two phonograph records (Schevill and Lawrence
1950; Schevill and Watkins 1962). The recordings sparked the curiosity of
investigators, who raised questions about the source and function of these
sounds. Since that time, researchers have engaged in attempts to determine
the exact mechanism and specific location for the production of odontocete
echolocation pulses, as well as their formation into a forward-projecting
sonar beam.
This chapter is a chronologic look at the quest to understand biosonar
signal generation, with an emphasis on how the accumulation of evidence
affected interpretation and speculation in the scientific debate. In many
ways, the fervor that arose over the earliest form-function questions in
odontocete echolocation was born from an overly simplistic view of the
degree to which aquatic adaptation could revamp and refine a sensory
system. Professor Norris (1964) cautioned us against such underestimation
in a passage that is apt today:
One fact has consistently emerged from recent biological studies, particularly in the
spheres of biophysics and anatomy, and it is that we humans have, in the past, usually
underestimated the refinements of animal adaptations. Accordingly, if we are to
establish a working hypothesis for cetacean echolocation and its anatomical correlates, it is probably better to expect sophistication and to attribute function to structure, than it is to be forced eventually to such a viewpoint from the more sparse
interpretation that structures, even complex ones, need not have a function. (Norris
1964,p.324)
Before we frame the historical perspectives of the scientific debate and
address the issues that currently surround the questions that remain, let me
109