Discoveries - Sound tracks
Communication - Eavesdropping on the lives of sperm whales
BBC Wildlife Magazine, January 2000
The secret life of one of the ocean's most elusive mammals, the sperm
could soon be revealed by intercepting its calls.
Understanding the behaviour of many marine mammals depends to a great
on tracking individuals. But photographing sperm whales - the method
commonly used to identify different animals by their characteristic tail and
fin markings - is difficult, because they spend most of their time widely
separated and at great depths, surfacing only briefly.
Sperm whales are highly vocal, making regular, loud clicks at a frequency
about one per second, which led scientist Michael Dougherty and colleagues
at Washington University to wonder whether an individual's identity might be
disclosed by its voice. "The sounds carry over long distances," says
Dougherty, "and it's likely that these whales can recognise different voices
and communicate with each other from afar in the ocean's darkness."
To find out if humans could listen in, Dougherty recorded whales off
coast of Norway and photographed each one at the surface to tally his
recordings. Using a computer to analyse the voices, he discovered the way
that sound changes during a click is individually distinct. Taking a sample
of 20 clicks for each animal, the computer programme proved to be
ninety-nine per cent accurate in matching the sound to its owner. "If enough
of a whale's voice is used," says Dougherty, "the system becomes virtually
Studies are now underway on larger groups of whales and on how clicks
change during a dive. But, already, a system that tracks known individuals
while automatically identifying new ones is a feasible goal. It may
eventually allow remote, shore-based monitoring using a sound-sensitive buoy
that Dougherty is designing.
Factfile - Valuable signatures
Like sperm whales, big brown bats Eptesicus fuscus produce individually
recognisable sounds. Stephen Burnett and Mitchell Masters at Ohio State
University, USA, have discovered that by recording the bats' high-pitched
echolocation calls and using a computer programme to separate and count the
individual calls in a single recording, they can estimate accurately the
number of bats in an area. This technique, which avoids the disturbance of
capture methods, may have wide application - about three-quarters of bat
species use echolocation.
Return to top
A recent study of Germany's Lake Constance has shown that some animals
respond to environmental degradation with rapid evolution.
In the late 1960s, the lake was polluted by phosphates (plant nutrients),
which resulted in an abundance of fast-growing cyanobacteria (blue-green
algae). Cyanobacteria are both toxic and nutritionally inferior to the green
algae normally eaten by waterfleas Daphnia galeata, which led Nelson
Hairston at Cornell University, USA, and colleagues to examine the impact of
Buried D. galeata eggs can survive in a dormant state for centuries
be aged from their position in the sediment that builds up on a lakebed. The
scientists realised that, by hatching eggs from various depths, an
evolutionary history could be revealed in living animals.
When D. galeata that were hatched from 1960s (pre-pollution)
eggs were fed
cyanobacteria, their growth was variably reduced. By the 1970s - at the
height of the pollution - the more susceptible animals had been eliminated,
leaving only those able to tolerate the poor diet, an ability which was
passed on to waterfleas of the 1990s. "It's a neat demonstration of
evolution by natural selection," says Hairston, "and shows how zooplankton
affected by pollution can, by evolving, play a significant part in the
natural control of its effects." (Nature, vol. 401, p446).
Return to top
Naked mole-rats produce huge litters - often 24 or more. Yet, though
mother has only 12 mammary glands to feed her brood, the peace of her East
African burrow is not disturbed by hungry pups fighting for food.
Puzzled by this flagrant disregard for the one-half rule - mammals,
generally, have half as many young as the number of mammary glands - Paul
Sherman of Cornell University and colleagues observed nursing behaviour in a
mole-rat colony. They discovered that young take turns suckling at the same
nipple. And, in spite of the sharing, there is plenty of milk to go round so
there are no tantrums (Journal of Mammalogy, vol. 80, pp720-33).
Like ants and other social insects, the nearly hairless and sightless
colonial rodents inhabit vast underground labyrinths, and there are divisions of
labour in reproduction and colony work. Within a group of around 75 closely
related animals, only one female, the queen, and up to three males reproduce
while workers and soldiers maintain and defend the colony. By feeding their
queen mother and helping her to care for large litters, the apparently altruistic
workers and soldiers are favouring the propagation of shared genes.
But why the relatively few mammary glands? The scientists think one
for each pup would be counterproductive due to the greater likelihood of
mastitis and mammary cancer.
Return to top
Yet another new species of muntjac deer has been discovered, this time
the mountain forests of a remote and little-explored area of northern Myanmar,
along the western escarpment of China's Yunnan province. The chestnut coloured
animal which has been described by George Amato and colleagues from the
Wildlife Conservation Society, based at New York's Bronx Zoo, is known as the
leaf deer to local villagers and has been given the scientific name Muntiacus
putaoensis. It stands just 50cm high at the shoulder, making it the world's
smallest deer. This latest advance in understanding of the muntjac group
follows recent discoveries of five species of large mammals in the Annamite
mountains of Laos and Vietnam (BBC Wildlife, July 1993, June 1994, March 1996
and October 1997) of which three are muntjac, and brings the total number of
known muntjac species to nine
The usual way to distinguish a new species from its relatives is by
typical specimens - impractical in this case because of the lack of suitable
examples of some muntjac species. Instead, the scientists separated the new
animal by comparing DNA from all members of the group using more readily
available tissue samples such as fragments of bone and skin (Animal
Conservation, vol. 2, pp1-7).
Such rapid identification by molecular genetic techniques can be a crucial
tool in conservation - while new species continue to be found in relatively
unexplored areas such as the forests of south-east Asia, prompt action is
needed to save them as their habitats are disappearing at alarming rates.
Return to top