According to our report on migratory birds, insectivores—birds that feed on insects—have experienced a major population decline ranging from 40% to 60%. Scientists have a theory on this phenomenon. According to them, when migratory birds return to Canada, the insects are not yet out because of climate change. As a result, the birds have nothing to eat, and that leads to a decline in their numbers. That's one scientific theory, but I am not sure whether it has been proven.
There is another explanation. The change in the birds' habitat in the south may have an impact. That's not clear, but it's a theory.