Threats to Birds

Loss of Habitat:
The total population of birds in North America has decreased by 2.9 billion (29%) in just 50 years (United Nations)
Cats:
In North America, cats are second only to habitat loss as the largest human-related cause of bird deaths. It’s estimated that cats kill 1.3–4 billion birds each year in the U.S. alone, with 69% of these kills attributable to feral or unowned cats. (Cornell Labs)
Window strikes:
Homes and other buildings one to three stories tall accounted for 44 percent of all bird fatalities, about 253 million bird deaths annually. Larger, low-rise buildings four to 11 stories high caused 339 million deaths. And high-rise buildings, 11 floors and higher, kill 508,000 total birds annually. (Cornell Labs) Collisions likely kill between 365 million and 1 billion birds annually in the United States. (Smithsonian)
Invasive species:
Invasive species out compete native species that have co-evolved with birds and insects to provide nutritious food, and shelter. The vast majority of baby birds are raised on caterpillars. Invasive species do not offer the same, if any, nutrition.