The regions in robins' brains responsible for singing and mating are shrinking when exposed to high levels of DDT, says new University of Alberta research--the first proof that natural exposure to a contaminant damages the brain of a wild animal.
"These residues have been persisting since the late 1960s--that's what is really disturbing," said Dr. Andrew Iwaniuk, a post-doctoral research fellow in the U of A's Department of Psychology. "It has been years since it has been used and still has this effect."
The new research, published in Behavioural Brain Research, strongly suggests that exposure to environmental levels of DDT causes significant changes in the brains of songbirds.
Previous studies have suggested that exposure to DDT residues affect the brain, but none have actually demonstrated it. The research team, including Iwaniuk's supervisor, psychology professor and Tier II Canada Research Chair Douglas Wong-Wylie, used American Robins to test the idea. Birds are more susceptible to the effects of pesticide residues and other contaminants in the environment than other animals. As well, American robins are often exposed to high levels of DDT and other chemicals because they rely heavily on earthworms as part of their diet. They specifically chose these birds in the Okanagan Valley because at that location they are exposed to high levels of DDT, but relatively low levels of other chemicals.
The researchers captured 18 nestlings and then hand-reared and observed them for two years. They then sectioned the brains and examined the size of several brain regions. "We found that the regions sensitive to reproductive hormones--song production and courtship behaviour--were most affected by DDT," said Iwaniuk. "Song production is extremely important in attracting a mate or to mark out a territory.
"The issue is not that DDT is killing these robins but if they are growing up in this one area and then move to another, they won't be able to attract any females."
These effects were most prominent in the males, some of which experienced up to a 30 per cent reduction in brain region size compared to males at lower DDT exposure levels.
Whether this also applies to other animals and humans is unclear because there is not yet a strong understanding of how these chemicals in the environment affect the brain, but it is possible that humans exposed to similar levels of DDT will also be at risk of neurological damage.
"The take-home message is that people need to be more cognizant of their use of pesticides and herbicides," said Iwaniuk. "People need to be careful about using chemicals in their homes or farms. Who knows the effects these will have down the road."
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