9
Echolocation in Dolphins
WHITLOW W.L. Au
1. Introduction
Echolocation is the process by which an organism projects acoustic signals
in order to obtain a sense of its surroundings from the echoes it receives.
In a general sense, any animal with a capability to hear can echolocate by
emitting sounds and listening to the echoes. A person in an empty room
can gain an idea of the size and shape of the room by emitting sounds and
listening to the echoes from the different walls. However, in this chapter
echolocation is used in a more specific sense in which an animal has a
very specialized capability to determine the presence of objects considerably smaller than itself, discriminate between various objects, recognize
specific objects, and localize objects in three-dimensional space (determining range and azimuth). Dolphins and bats have this specialized capability
of echolocation.
A dolphin's ability to survive and thrive in an aquatic environment is
maximized by its ability to echolocate. Acoustic energy propagates in water
more efficiently than almost any other form of energy, making the use of
acoustics ideal for the aquatic environment. Many species of dolphins can
be found in shallow offshore waters, bays, and rivers where the water can
be extremely turbid with very limited underwater visibility. Under these
conditions, the ability to echolocate becomes critical for navigating, locating and catching prey, and avoiding predators.
The echolocation system of a dolphin can be broken down into three subsystems, the transmission, reception, and signal processing/decision making
subsystems. The transmission system consists of the sound producting
mechanism, acoustic propagation from within the head of the dolphin out
into the water, and the characteristics of the signals traveling in the surrounding environment. The sound production mechanism is discussed by
Cranford in Chapter 3 and the propagation of the signals through the
dolphin's head is addressed by Aroyan et al. in Chapter 10. The receiving
subsystem consists of the auditory system of the animal, and its capabilities
depend on the characteristics of the peripheral and higher auditory centers
364
Echolocation in Dolphins
WHITLOW W.L. Au
1. Introduction
Echolocation is the process by which an organism projects acoustic signals
in order to obtain a sense of its surroundings from the echoes it receives.
In a general sense, any animal with a capability to hear can echolocate by
emitting sounds and listening to the echoes. A person in an empty room
can gain an idea of the size and shape of the room by emitting sounds and
listening to the echoes from the different walls. However, in this chapter
echolocation is used in a more specific sense in which an animal has a
very specialized capability to determine the presence of objects considerably smaller than itself, discriminate between various objects, recognize
specific objects, and localize objects in three-dimensional space (determining range and azimuth). Dolphins and bats have this specialized capability
of echolocation.
A dolphin's ability to survive and thrive in an aquatic environment is
maximized by its ability to echolocate. Acoustic energy propagates in water
more efficiently than almost any other form of energy, making the use of
acoustics ideal for the aquatic environment. Many species of dolphins can
be found in shallow offshore waters, bays, and rivers where the water can
be extremely turbid with very limited underwater visibility. Under these
conditions, the ability to echolocate becomes critical for navigating, locating and catching prey, and avoiding predators.
The echolocation system of a dolphin can be broken down into three subsystems, the transmission, reception, and signal processing/decision making
subsystems. The transmission system consists of the sound producting
mechanism, acoustic propagation from within the head of the dolphin out
into the water, and the characteristics of the signals traveling in the surrounding environment. The sound production mechanism is discussed by
Cranford in Chapter 3 and the propagation of the signals through the
dolphin's head is addressed by Aroyan et al. in Chapter 10. The receiving
subsystem consists of the auditory system of the animal, and its capabilities
depend on the characteristics of the peripheral and higher auditory centers
364