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Historical pesticide applications coincided with an altered diet of aerially-foraging insectivorous chimney swifts

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50 years of bird poop links DDT with changing bird menus

Populations of insect-eating birds in North America, such as the chimney swift, have been in long-term decline for unknown reasons, but new research suggests that DDT and bird diet may have played a role.

Chimney swifts gather in large groups each night to roost in chimneys. After several decades of swifts using a large chimney at Queen’s University’s Fleming Hall, Chris Grooms discovered at its base a remarkably well-preserved deposit, representing about 50 years of bird droppings.

Analysis of the 2 m high accumulation of droppings showed that DDT use peaked at the same time that there was a dramatic reduction in the abundance of beetles (insects especially susceptible to DDT) in the diet of swifts. This illustrates an impact of DDT that adds to its already infamous role in the thinning of eggshells.

“Decreased consumption of beetles can be linked with swift population declines over several decades,” says lead author Joe Nocera, an adjunct professor at Queen’s and research scientist with the Ontario Ministry of Natural Resources. “It is startling to see first-hand how destructive DDT was and the degree of carry-over effects on non-target species.”

The study shows that the peak of DDT use in the mid-20th century occurred when swifts switched from foraging primarily on beetles to eating lower-quality food. Today, swift populations have declined low enough that they are considered a Threatened Species in Ontario and across Canada.

"We already knew that DDT spraying in the 1950s and 60s reduced beetle populations in this area,” says co-author Linda Kimpe of the University of Ottawa. “But our study is the first to show how DDT may have altered the diets of insect-eating birds like swifts."

“Certainly there are many other deposits in large chimneys around North America and elsewhere, forming important environmental time capsules,” says biology professor and co-author John P. Smol, Canada Research Chair in Environmental Change, and previous winner of the Natural Sciences and Engineering Research Council of Canada (NSERC) Herzberg Gold Medal as Canada’s top scientist. “It may be a stinky job, but someone has to do it!”

Other members of the research team include University of Ottawa professor Jules Blais, Trent University’s David Beresford and Leah Finity, several Queen’s University researchers: Christopher Grooms, Kurt Kyser, and Neal Michelutti, and Thompson Rivers University professor Matthew Reudink. Funding for the research comes from NSERC and the Ontario Ministry of Natural Resources.

These findings were published in the prestigious international journal Proceedings of the Royal Society-B.
 

PLEASE NOTE: A PDF copy of the study can be obtained from the Proceedings of the Royal Society website, or contact Dr. John Smol at smolj@queensu.ca or Joseph Nocera joe.nocera@ontario.ca for a copy.

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