DDT is famous — infamous — for its effects on birds including eggshell thinning. Research recently published in the Proceedings of the Royal Society B has found that DDT can be linked to the long-term decline of insect-eating birds in North America.
Researchers from the Paleoecological Environmental Assessment and Research Lab (PEARL), analyzed 50 years of bird droppings inside a large chimney no longer in use on the campus of Queen’s University in Ontario. Chris Grooms, a PEARL research technician, discovered the deposit in the chimney. That half-century of guano provided evidence that DDT and bird diet have played a role in the long-term decline of insect-eating birds.
The chimney had once been a roosting point for chimney swifts, whose numbers have been declining; the birds have been listed as threatened for several years by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC). As summarized on Science Daily, the researchers found that the use of DDT had peaked at the very same time as there was “a dramatic reduction in the abundance of beetles — insects especially susceptible to DDT — in the diet of swifts,” after analysis of a pile of droppings.
A 50-year pile of bird droppings in an abandoned chimney is, of course, not the pleasantest of materials to study. It was indeed a “stinky job, but someone has to do it ,” commented biology professor and co-author John P. Smol, Canada Research Chair in Environmental Change. For archaeologists, koprolites — the preserved dung of ancient animals — provides valuable information about the diet, health and habits of animals long lost to time. One of the difficulties in figuring out the causes of the insectivorous bird population has been a sheer lack of long-term data: The chimney’s deposit enabled the scientists to study the diet of chimney swifts from 1948 – 1992, a period of 48 years and provide further proof that DDT, by dramatically altering the population of insects, has had similar effects on swifts and other birds.
While it hardly seems necessary to note the adverse effects of DDT on birds, fish, mammals, humans and many more animals and the environment as a whole, the Canadian scientists’ study shows how pesticide use has not only immediate consequences but long-term, far-reaching ones, and provides compelling further evidence to why it is necessary to continue to ban the use of DDT and seek sustainable alternatives — and to ensure the survival of chimney swifts.
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Photo by dominic sherony