North American birds are absolutely in decline. From this article [1], the overall population has decreased by about 1.5 billion birds since 1970. For some groups of species, for instance, aerial insectivores [2], things are much worse. For instance, the population of bank and barn swallows, chimney swifts and common nighthawks has decreased by 70% over the past twenty years alone.

The Christmas Bird Survey is done after most birds have migrated and so captures data on the relative abundance of resident birds, which as a group, are doing better than birds in North America overall.

[1] https://www.theglobeandmail.com/technology/science/report-fi... [2] http://www.bsc-eoc.org/download/BWCwi08.pdf

There's hard data from a study over 27 years in Germany on the decline of insects, references below:

> sabertoothed

In some nature protected areas in Germany, researchers [1] have reported a 75% decline in flying insects over 27 years. Study is from Oct 2017. This is alarming.

[1] http://journals.plos.org/plosone/article?id=10.1371/journal.....

There are many insectivorous bird species. We've become more efficient at killing insects, and thus depressing their populations. Agreed?

What are the insectivorous birds eating if their populations aren't declining?

Did you not read the article? It says there are less birds.

Not a decline in variety. The birds are going away.