- Hyperactive fish, stupid frogs, fearless mice and seagulls
that fall over. It sounds like a weird animal circus, but this is no freak
show. Animals around the world are increasingly behaving in bizarre ways,
and the cause is environmental pollution.
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- The chemicals to blame are known as endocrine disruptors,
and range from heavy metals such as lead to polychlorinated biphenyls (PCBs)
and additives such as bisphenol A.
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- For decades, biologists have known that these chemicals
can alter the behaviour of wild animals. And in recent years it has become
clear that pollutants can cause gender-bending effects by altering animals'
physiology, particularly their sexual organs.
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- But now two major reviews have revealed that the chemicals
are having a much greater impact on animal behaviour than anyone suspected.
Low concentrations of these pollutants are changing both the social and
mating behaviours of a raft of species. This potentially poses a far greater
threat to survival than, for example, falling sperm counts caused by higher
chemical concentrations.
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- Snails and quails
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- The two research teams have independently collected evidence
revealing the effects on egrets and gulls, snails, quails, rats and macaques,
minnows, mosquito fish, falcons and frogs. Behaviours altered include mating
and parenting, nest building, learning, predator avoidance, foraging, activity
levels and even balance.
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- In one study, for instance, male starlings exposed to
dicrotophos insecticide decreased their singing, displaying, flying and
foraging activities by 50%. And newts exposed to low levels of the pesticide
endosulfan found it harder to sniff out the attractive pheromones of potential
mates.
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- Researchers have also shown that increasing numbers of
male western gulls hatched from eggs exposed to DDT attempt to mate with
each other. In recent years, scientists have also found that lead affects
the balance of gulls, while atrazine makes goldfish hyperactive and the
chemical TCDD makes the play behaviour in macaques rougher.
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- Despite this wealth of evidence, these effects have gone
largely unnoticed by toxicologists, says Ethan Clotfelter of Amherst College
in Massachusetts, lead author of one of the reviews, published in August
2004 in Animal Behaviour (vol 68, p 465).
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- Missing a trick
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- Not only are we failing to acknowledge the scale of the
problem caused by endocrine disruptors, but toxicologists may be missing
a trick: changes in animal behaviour could be an early warning that certain
chemicals are harmful. "You might see behavioural effects long before
you see a population crash," Clotfelter says.
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- Dustin Penn and Sarah Zala of the Konrad Lorenz Institute
of Comparative Ethology at the Austrian Academy of Sciences in Vienna agree.
They have just published a second review of the effects of endocrine disruptors
in the same journal (DOI: 10.1016/j.anbehav.2004.01.005). "The most
important point is the incredible amount of evidence that this is a widespread
problem," Penn says.
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- Both research groups say that biologists must wake up
to the fact that endocrine disruptors might explain bizarre behaviour in
wild animals. And both reviews reveal that different concentrations of
chemicals can have unexpected effects.
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- Male mice exposed to low doses of some pesticides increase
their scent-marking behaviour, for instance, but decrease it when exposed
to higher concentrations.
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- Damaging doses
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- "Pollutants that have been considered safe when
tested at medium doses could have damaging effects at lower doses,"
Penn and Zala warn in their review. And conversely, toxicologists might
exaggerate the risks posed by higher doses.
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- Other behavioural biologists back the authors' call for
biologists and toxicologists to work more closely to determine the scale
of the problem. "It's been decades since the first evidence appeared
that chemicals in the environment can influence behaviour," says John
McCarty of the University of Nebraska in Omaha, who researches the impact
of pollutants on birds.
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- "It seems to me that this body of evidence was pushed
to the background while most environmental scientists and regulators focused
on mortality and cancer rates [caused by endocrine disruptors and other
pollutants]."
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- The US Environmental Protection Agency says it cannot
provide a detailed comment on the research, but promises it will investigate
further. "We'll review these two scientific articles as we continue
to develop an endocrine screening and testing programme," a spokeswoman
told New Scientist.
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- Geoff Brighty, ecosytems science manager at the UK Environment
Agency, agrees that studying the effects of chemicals on animal behaviour
should be given a higher priority. "It is becoming recognised that
behaviour is important to look at to make sure a chemical is safe, and
we ignore it at our peril."
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