Pollution Triggers Bizarre Behaviour in Animals
By Andy Coghlan
Wednesday 01 September 2004
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.
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.
For decades, biologists have known that these chemicals can alter the
behavior 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.
But now two major reviews have revealed that the chemicals are having
a much greater impact on animal behavior than anyone suspected. Low
concentrations of these pollutants are changing both the social and mating
behaviors of a raft of species. This potentially poses a far greater threat
to survival than, for example, falling sperm counts caused by higher
Snails and Quails
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. Behaviors altered include mating
and parenting, nest building, learning, predator avoidance, foraging,
activity levels and even balance.
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
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 behavior in macaques rougher.
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 Behavior (vol 68, p 465).
Missing a Trick
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 behavior could be an early warning that certain chemicals are
harmful. "You might see behavioral effects long before you see a population
crash," Clotfelter says.
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.
Both research groups say that biologists must wake up to the fact that
endocrine disruptors might explain bizarre behavior in wild animals. And
both reviews reveal that different concentrations of chemicals can have
Male mice exposed to low doses of some pesticides increase their
scent-marking behavior, for instance, but decrease it when exposed to
"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
Other behavioral 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 behavior," says John McCarty of the University of
Nebraska in Omaha, who researches the impact of pollutants on birds.
"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
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 program," a spokeswoman told New Scientist.
Geoff Brighty, ecosystems science manager at the UK Environment
Agency, agrees that studying the effects of chemicals on animal behavior
should be given a higher priority. "It is becoming recognized that behavior
is important to look at to make sure a chemical is safe, and we ignore it
at our peril."