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P.L. Tyack and c.w. Clark
cause less damage to marine mammals than would be anticipated in the
absence of such a mechanism (Richardson et al. 1995).
2.4.2 When Do Odontocetes Use Sound to Detect Prey?
Extensive experiments prove that dolphins have a highly sophisticated
echolocation system, with abilities to detect a small metal sphere at ranges
near 100m (Au, Chapter 9). However, we know surprisingly little about how
dolphins use echolocation in the wild. Many species of bats produce a constant series of echolocation pulses as they fly during the twilight hours. The
steady series of orientation clicks is punctuated by a buzz of clicks with
rapidly decreasing inter-click intervals as the bat detects and closes in on a
prey item (Griffin et al. 1960). Vision is so limited in most marine environments that one might expect dolphins to echolocate almost continuously to
orient and avoid obstacles. In contrast to flying bats, however, bottlenose
dolphins in the turbid inshore waters near Sarasota, Florida, often swim for
tens of minutes without producing any clicks (Nowacek 1999). When dolphins in Sarasota feed during the day, the role of ycholocation in foraging
depends upon the feeding habitat. When feeding in clear water over sand, or
along the border between sandy bottom and grass flats, dolphins seldom
echolocate, but echolocation is an important part of the search phase of
feeding when dolphins are feeding over grass flats, where the prey fish can
hide among the grass. Bottlenose dolphins in Little Bahama Bank also use
echolocation in the search and pursuit phases of feeding on sand dabs buried
in sand (Herzing, Chapter 5). These dolphins actually produce echolocation
clicks before submerging their rostra into the sand to find buried fish. This
suggests that they can echolocate to detect the fish buried in sand.
When patterns of echolocation are tested in carefully controlled experiments, most dolphins appear to listen for the echo of the last click before
making another click. This means that there is a clear relationship between
inter-click interval and the range to the target. Studies of dolphins in captivity (Wood 1953) and in the wild in western Australia report that dolphins
often produce a buzzlike series of clicks as they chase or close in on fish.
Studies of Clicks in wild narwhals (Monodon monocerus) also found patterns of regular clicks like the orientation clicks of bats and buzzes like the
terminal buzz as a bat closes on prey (Miller et al. 1995). Miller et al. (1995)
suggest that these patterns do in fact reflect orientation/detection and
pursuit phases of foraging mediated by echolocation. If odontocetes must
produce a distinctive echolocation signal as they close in on prey in order
to optimize the echolocation process, then this could alert other animals
nearby to the presence of prey. Even if these signals are produced by a
dolphin for echolocation, if the prey tend to aggregate, then other dolphins
nearby could benefit from intercepting the signals and approaching to look
for prey (as discussed for bats by Fenton 1995). We cannot assume that
P.L. Tyack and c.w. Clark
cause less damage to marine mammals than would be anticipated in the
absence of such a mechanism (Richardson et al. 1995).
2.4.2 When Do Odontocetes Use Sound to Detect Prey?
Extensive experiments prove that dolphins have a highly sophisticated
echolocation system, with abilities to detect a small metal sphere at ranges
near 100m (Au, Chapter 9). However, we know surprisingly little about how
dolphins use echolocation in the wild. Many species of bats produce a constant series of echolocation pulses as they fly during the twilight hours. The
steady series of orientation clicks is punctuated by a buzz of clicks with
rapidly decreasing inter-click intervals as the bat detects and closes in on a
prey item (Griffin et al. 1960). Vision is so limited in most marine environments that one might expect dolphins to echolocate almost continuously to
orient and avoid obstacles. In contrast to flying bats, however, bottlenose
dolphins in the turbid inshore waters near Sarasota, Florida, often swim for
tens of minutes without producing any clicks (Nowacek 1999). When dolphins in Sarasota feed during the day, the role of ycholocation in foraging
depends upon the feeding habitat. When feeding in clear water over sand, or
along the border between sandy bottom and grass flats, dolphins seldom
echolocate, but echolocation is an important part of the search phase of
feeding when dolphins are feeding over grass flats, where the prey fish can
hide among the grass. Bottlenose dolphins in Little Bahama Bank also use
echolocation in the search and pursuit phases of feeding on sand dabs buried
in sand (Herzing, Chapter 5). These dolphins actually produce echolocation
clicks before submerging their rostra into the sand to find buried fish. This
suggests that they can echolocate to detect the fish buried in sand.
When patterns of echolocation are tested in carefully controlled experiments, most dolphins appear to listen for the echo of the last click before
making another click. This means that there is a clear relationship between
inter-click interval and the range to the target. Studies of dolphins in captivity (Wood 1953) and in the wild in western Australia report that dolphins
often produce a buzzlike series of clicks as they chase or close in on fish.
Studies of Clicks in wild narwhals (Monodon monocerus) also found patterns of regular clicks like the orientation clicks of bats and buzzes like the
terminal buzz as a bat closes on prey (Miller et al. 1995). Miller et al. (1995)
suggest that these patterns do in fact reflect orientation/detection and
pursuit phases of foraging mediated by echolocation. If odontocetes must
produce a distinctive echolocation signal as they close in on prey in order
to optimize the echolocation process, then this could alert other animals
nearby to the presence of prey. Even if these signals are produced by a
dolphin for echolocation, if the prey tend to aggregate, then other dolphins
nearby could benefit from intercepting the signals and approaching to look
for prey (as discussed for bats by Fenton 1995). We cannot assume that