They must have drunk a lot.
Birds have very “fast” metabolisms, and relative to their size it takes a lot of imbibing to get them “drunk”.
You can often see them getting drunk under trees whose fruit has fallen and fermented.
Elephant eats ripe fruit. Elephant drinks lots of water. Fruit turns into alcohol. Elephant staggers around. Birds too eh?!
When I was a kid, there was a mulberry tree in our yard. The flies got drunk and they couldn't fly. They just spun around in circles on the ground.
nothing as mean as a drunk Canadian goose