Birds fall out of trees when drunk I also fall over, have difficulty flying and run into things when drunk so theory seems plausible.

Each wet season drunken red-collarred lorikeets abound in the Northern Territory. (Credit: Getty Images)

"Each wet season in northern Australia dozens of colorful lorikeets have to be rescued because they appear drunk, fall out of trees and even get a hangover-like sickness. No one knows quite what's going on, but the best explanation is they get smashed from fermented fruit. From the story: 'Experts say they are not sure if the lorikeets are actually drunk, but they do have tell-tale symptoms. "They exhibit odd behavior like falling over or difficulty flying [and] they keep running into things," says Darwin vet Dr Stephen Cutter from The Ark Animal Hospital.'"