How chimney swifts’ diet affects population size



A recent study in Canada recently revealed another factor that has played a role in the decline of chimney swifts. Chris Grooms, a research technician at Queen’s University, discovered an abandoned five-story chimney in a campus building that contained a pile of swift poop more than six feet deep.






Beetles are more sensitive to DDT than true bugs, so beetles became less common as DDT use increased through the 1940s, 50s and 60s. This caused swifts to eat more true bugs than beetles.


Over time the use of DDT forced swifts to consume more true bugs, an inferior food, and fewer beetles, simply because beetles became less common. So they had to spend more time feeding on the wing and less time taking care of nestlings. And unfortunately, there is no evidence the percentage of beetles in the diet increased after the banning of DDT in the early 1970s.


DDT is best known for its role in the decline of bald eagles, ospreys, brown pelicans and peregrine falcons. Birds exposed to DDT during the 1940s, 50s and 60s became unable to lay eggs with normal shells, a phenomenon that came to be known as “egg-shell thinning.” During incubation, eggs would crack and embryos died.

As a result, successful reproduction almost came to a halt and populations of affected species declined quickly. Most of these affected species became classified as “endangered.” Since DTT was outlawed, these species have made remarkable recoveries, and each that I mentioned has been removed from the “endangered” list.


One of the results of the Canadian chimney swift poop study is that ecologists are beginning to wonder how far beyond egg-shell thinning the effects of DDT reached. If it altered the diet of chimney swifts, did it also change the diet of other insectivorous species such as swallows, flycatchers, warblers, vireos and maybe even nighthawks and whip-poor-wills. It’s too bad other species haven’t left behind repositories of droppings that could be studied in the manner the Canadian swifts have been.

When swifts return in April, you can recognize them by their constant twitters, cigar-shaped body and long narrow wings. They fly almost continuously, always in search of flying insects.




Up-to-date agriculture news in your inbox!



Receive emails as this discussion progresses.