4. Acoustic Communication in Whales and Dolphins
171
reverberation. Several biologists have even suggested that marine mammals
might be able to sense echoes of low-frequency vocalizations from distant
bathymetric features in order to orient or navigate (Norris 1966, 1969;
Payne and Webb 1971; and Thompson et aI.1979). While these speculations
have been amplified by acoustic modeling (e.g., Ellison et al. 1987; Clark
and Ellison 1997), it is important to note that there is no experimental
verification that cetaceans use echoes from the targets described in this
paragraph. It will be challenging to design convincing experiments for
cetaceans at sea.
2.6 Detection and Categorization of the Calls
of Conspecijics
Almost all of the field work on cetacean acoustic behavior has studied
intraspecific communication. This should be more familiar to most readers
than the topics of how animals may respond to sounds of other species, or
how animals may use sound to explore their environment. The basic behavioral ecology of acoustic communication is the same for terrestrial and
marine animals. In this section I will review some of the basic functional
categories of communication signals, with some discussion relating these
functional categories to life in the sea.
There appears to be a correlation between the types of social bonds
and communication signals seen in different cetacean groups (Tyack 1986).
Individual-specific signals have been reported for species with strong
individual social bonds such as bottlenose dolphins; group-specific vocal
repertoires have been reported for species with stable groups such as killer
whales, and population-specific advertisement displays have been reported
among species such as humpback whales where adults appear to have
neither stable bonds nor stable groups.
2.6.1 Contact Calls and Recognition Signals
Most cetaceans are both social and highly mobile. Animals that rely on
other individuals often move out of sight of each other on an hourly basis
and have evolved communication mechanisms for maintaining contact
and for reuniting with one another. The most basic and common bond in
mammals is that between mother and young. Cetacean calves have an
unusual combination of a long period of dependence, coupled with precocious sensory and locomotor skills. Few cetaceans wean before half a year,
and some of the larger odontocetes may continue to suckle for more than
a decade (Best 1979, Kasuya and Marsh 1984). Unlike most terrestrial
animals with parental care, cetaceans have no nests, refuges, or temporary
hiding places where a newborn can rest, nor can a parent physically carry
a nonambulatory infant. All cetacean infants must be able to swim independently and must surface to breathe soon after birth. Even though wild
171
reverberation. Several biologists have even suggested that marine mammals
might be able to sense echoes of low-frequency vocalizations from distant
bathymetric features in order to orient or navigate (Norris 1966, 1969;
Payne and Webb 1971; and Thompson et aI.1979). While these speculations
have been amplified by acoustic modeling (e.g., Ellison et al. 1987; Clark
and Ellison 1997), it is important to note that there is no experimental
verification that cetaceans use echoes from the targets described in this
paragraph. It will be challenging to design convincing experiments for
cetaceans at sea.
2.6 Detection and Categorization of the Calls
of Conspecijics
Almost all of the field work on cetacean acoustic behavior has studied
intraspecific communication. This should be more familiar to most readers
than the topics of how animals may respond to sounds of other species, or
how animals may use sound to explore their environment. The basic behavioral ecology of acoustic communication is the same for terrestrial and
marine animals. In this section I will review some of the basic functional
categories of communication signals, with some discussion relating these
functional categories to life in the sea.
There appears to be a correlation between the types of social bonds
and communication signals seen in different cetacean groups (Tyack 1986).
Individual-specific signals have been reported for species with strong
individual social bonds such as bottlenose dolphins; group-specific vocal
repertoires have been reported for species with stable groups such as killer
whales, and population-specific advertisement displays have been reported
among species such as humpback whales where adults appear to have
neither stable bonds nor stable groups.
2.6.1 Contact Calls and Recognition Signals
Most cetaceans are both social and highly mobile. Animals that rely on
other individuals often move out of sight of each other on an hourly basis
and have evolved communication mechanisms for maintaining contact
and for reuniting with one another. The most basic and common bond in
mammals is that between mother and young. Cetacean calves have an
unusual combination of a long period of dependence, coupled with precocious sensory and locomotor skills. Few cetaceans wean before half a year,
and some of the larger odontocetes may continue to suckle for more than
a decade (Best 1979, Kasuya and Marsh 1984). Unlike most terrestrial
animals with parental care, cetaceans have no nests, refuges, or temporary
hiding places where a newborn can rest, nor can a parent physically carry
a nonambulatory infant. All cetacean infants must be able to swim independently and must surface to breathe soon after birth. Even though wild