So says New Scientist story about Berkeley hummingbird researcher Chris Clark.
When male Anna's hummingbirds' do courtship flights, they do dives and loops, causing them to sustain accelerations that would leave a human being out cold. (Fighter pilots pass out at 7 g. Anna's hummingbirds can do 10 g).
There's a video with the story, but I can't seem to get it started.
Here's a more detailed take on the story from Not Exactly Rocket Science.
Here's a male Anna's hummingbird I photographed on my street in March.