They have determined that perhaps the reason for the bird population declines, when it comes to aerial insectivores, is related to the insect population declines.
Seems logical to me.
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.
