Have you noticed that swallows, swifts, martins and whip-poor-wills are missing from our sky?

Museum bird collections

A new recently published study looking at the diets of some bird species over the last century found drastic changes in the insects being eaten. (Shane Fowler/CBC)

“You are what you eat” is the guiding principle behind a new study comparing the diet of birds today with that of birds dead for more than a century.
The results show large changes in the diets of aerial insectivores, or birds such as swallows, swifts, martins and whip-poor-wills that consume insects while in mid-flight.
Today, the bulk of the birds’ diet is made up of small insects at the lower end of the food web, or at a lower “trophic” level, the researchers say.
“Higher up on a trophic level might be steak,” said Joe Nocera, an assistant professor of forestry and environmental management at the University of New Brunswick and one of the authors of the paper.
“Lower on a trophic level might be a salad. You’d have to eat a lot more salad to make up for that steak.”

Choice of insects shrinks

For example, whip-poor-wills today still have to eat insects, Nocera said, but what they have to choose from isn’t as beneficial as it was 100 years ago.

Joe Nocera
Joe Nocera, an assistant professor of forestry and environmental management at UNB, is an author of the paper, along with Philina English and David Green of Simon Fraser University. (Shane Fowler/CBC)

Using stable isotopes, or molecules found in the food eaten by birds, researchers have been able to map the changes in diet for species such as whip-poor-wills back to the 1800s.

“It’s a species that used to be common in New Brunswick, but isn’t anymore,” Nocera said. “So we looked at Ontario populations. And we wanted to know what’s driving their population declines over the past century.”
Nocera said most species of aerial insectivores, including swifts and swallows, have been in severe decline and he  thinks it’s most likely a response to declines in insect populations.
“But we don’t know that,” he said. “We have terrible historical records on insect abundance in history.”

READ THE ENTIRE ARTICLE: Bug diet of birds has dramatically declined in quality, researchers find – New Brunswick – CBC News

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