There are 3 billion fewer birds in North America than there were in 1970.
This data is from a 2019 Science paper that combined 48 years of citizen-science bird counts with continent-wide weather radar tracking nighttime migration.
The losses are concentrated in the birds people see most often: grassland birds (down 53%, 700 million gone), forest birds (1 billion gone), and shorebirds (down 37%). Even common species (blackbirds, swallows, warblers) are vanishing.
Habitat loss is the biggest reason, but the rest of the list is short and largely fixable for the average person.
1. Pesticides killing the insects birds eat.
2. Outdoor cats kill an estimated 2.4 billion US birds annually.
3. Window collisions killing roughly a billion more. Lawn chemicals.
4. Light pollution disrupting migration.
What you can do, ranked by impact: keep cats indoors, treat your windows for bird strikes, plant native trees and shrubs, stop spraying pesticides, leave the leaves and seed heads through winter, and turn off outdoor lights at night during spring and fall migration.
No one person killed 3 billion birds, obviously, but your yard can be a part of the solution that rebuilds their numbers.