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P.L. Tyack and c.w. Clark
bottlenose dolphin calves are completely dependent upon their mothers,
they swim out of sight of the mother within the first few weeks of life
(Smolker et al. 1993). During the first few weeks of life, a right whale calf
spends more than 90% of the time with the mother, but by two to three
months of age, they may spend 20% to 30% of the time away from the
mother (Taber and Thomas 1982). Right whale calves leave more often than
they approach during this period, while mothers maintain contact with
the infant, approaching more often than they leave. Cetaceans can see and
hear well at birth, and newborn odontocetes are able to vocalize in the few
species tested (e.g., Caldwell et al. 1990).
Not only is it advantageous for mother and young to keep in contact with
one another, but once they have separated, it is also clearly to their benefit
to have some mechanism for reuniting with the correct individual, or each
may incur serious costs. If a mother accepts the wrong infant, the infant may
steal resources such as milk. Even more important, the mother may reduce
her chances of regaining contact with her actual offspring again. Cetaceans
give birth to a single offspring, with the shortest calving interval being one
year. Reproductive success depends upon significant parental care, so a
reduction in care by the mother carries a subsequent risk to the young and
a significant potential cost to the mother. If the infant accepts the wrong
mother, there are also risks. At least among dolphins, adult females find
infants attractive, and often will allomother an infant (Mann and Smuts
1998). However, these allomothers may not provide care as good as the
actual mother, and infants left for prolonged periods with an allomother
may have a decreased survival probability.
Many mammals use visual and acoustic cues to recognize their young
from a distance. The mother typically then confirms calf recognition using
olfactory cues at close range before she allows the young begin to suckle.
While olfactory cues were probably important in the terrestrial ancestors
of cetaceans (Alexander 1977, 1978; Alexander and Shillito 1977), and
appear to also be used in pinnipeds (Trillmich 1981), the olfactory sense has
been lost in modern cetaceans. The loss of olfaction places a greater
reliance on acoustic cues for mother-infant recognition. Birds have reduced
olfaction and also rely upon acoustic cues for parent-offspring recognition.
There is evidence in swallows that the demands of parent-offspring
recognition not only have selected for the begging calls that are used for
recognition to be more individually distinctive, but also have selected for
more rapid discrimination of begging calls by adults (Loesche et al. 1991).
There thus appears to be a selective advantage for those individuals whose
recognition systems have certain attributes that are best adapted for the
particular situation confronting that population of individuals. For
example, in species where the ecology increases the risk of misallocation
of care, selection favors those individuals who possess specialized auditory
processes that increase the chances of mother-infant recognition and
reunion.
P.L. Tyack and c.w. Clark
bottlenose dolphin calves are completely dependent upon their mothers,
they swim out of sight of the mother within the first few weeks of life
(Smolker et al. 1993). During the first few weeks of life, a right whale calf
spends more than 90% of the time with the mother, but by two to three
months of age, they may spend 20% to 30% of the time away from the
mother (Taber and Thomas 1982). Right whale calves leave more often than
they approach during this period, while mothers maintain contact with
the infant, approaching more often than they leave. Cetaceans can see and
hear well at birth, and newborn odontocetes are able to vocalize in the few
species tested (e.g., Caldwell et al. 1990).
Not only is it advantageous for mother and young to keep in contact with
one another, but once they have separated, it is also clearly to their benefit
to have some mechanism for reuniting with the correct individual, or each
may incur serious costs. If a mother accepts the wrong infant, the infant may
steal resources such as milk. Even more important, the mother may reduce
her chances of regaining contact with her actual offspring again. Cetaceans
give birth to a single offspring, with the shortest calving interval being one
year. Reproductive success depends upon significant parental care, so a
reduction in care by the mother carries a subsequent risk to the young and
a significant potential cost to the mother. If the infant accepts the wrong
mother, there are also risks. At least among dolphins, adult females find
infants attractive, and often will allomother an infant (Mann and Smuts
1998). However, these allomothers may not provide care as good as the
actual mother, and infants left for prolonged periods with an allomother
may have a decreased survival probability.
Many mammals use visual and acoustic cues to recognize their young
from a distance. The mother typically then confirms calf recognition using
olfactory cues at close range before she allows the young begin to suckle.
While olfactory cues were probably important in the terrestrial ancestors
of cetaceans (Alexander 1977, 1978; Alexander and Shillito 1977), and
appear to also be used in pinnipeds (Trillmich 1981), the olfactory sense has
been lost in modern cetaceans. The loss of olfaction places a greater
reliance on acoustic cues for mother-infant recognition. Birds have reduced
olfaction and also rely upon acoustic cues for parent-offspring recognition.
There is evidence in swallows that the demands of parent-offspring
recognition not only have selected for the begging calls that are used for
recognition to be more individually distinctive, but also have selected for
more rapid discrimination of begging calls by adults (Loesche et al. 1991).
There thus appears to be a selective advantage for those individuals whose
recognition systems have certain attributes that are best adapted for the
particular situation confronting that population of individuals. For
example, in species where the ecology increases the risk of misallocation
of care, selection favors those individuals who possess specialized auditory
processes that increase the chances of mother-infant recognition and
reunion.