A bird is an animal that is characterized by feathers, a beak with no teeth, and the laying of hard shelled eggs. There are many species of birds. Some are wild, some are domesticated, and some are consumed by people for food.
A beat-up old flying car passed the DeLorean time machine on Skyway C25 on October 21, 2015, which displayed a bumper sticker reading I brake for birds!, along with two others reading Littering can kill! and This summer, do something a robot can't do — pick grapes!
Birds evolved from dinosaurs. In the Cretaceous Period, Verne Brown bonded with a friendly pteranodon that he named "Donny". His father, Doc Brown, told Verne that he had to leave Donny behind when they left in the DeLorean time machine just before the meteor that caused the extinction of the dinosaurs hit the Earth. When they returned to 1991, Verne saw a bird that resembled Donny. He wondered if it was his descendant.
Along with being a bird, chicken was also an insult used to call people cowards. Martin McFly and his brother's great-great-grandson Marty McFly had a complex where they would try to prove themselves to be brave whenever someone called them a coward or a chicken, even if the situation was not in their favor. Martin ended up stabbed and killed by a Bowie knife due to this problem, but Marty overcame it when he was told about Martin by Seamus in 1885.
Additionally, a term for people who are frequently thrown in jail is jailbird, which Joey Baines was referred to by Marty.
When Marty is questioning how Biff ended up with two brothers in the alternate 1986, Riff Tannen brought up the metaphor for explain sex which is "The Bird and the Bees" (though Riff said bugs instead of bees).
On April 22, 1990, Doc showed Doogie Howser and other physicians at St. Terra Hospital the current condition of the environment and the animals (including several species of birds) suffering the situation.
Behind the scenes
Most of the early video games based on the Back to the Future trilogy didn't faithfully adapt the source material. Back to the Future, a Japanese platform game for the MSX computer, contained stages where Marty McFly had to dodge birds that would fly towards him. This never happened in the film.
- Back to the Future (Blue Bird Motel)
- Back to the Future Part II (Blue Bird Motel)
- Back to the Future Part II novelization (Car bumper sticker, page 15)
- Back to the Future Part III (Blue Bird Motel)
- The Earth Day Special (Non-canonical appearance)
- Back to the Future: The Animated Series
- Back to the Future (Harvey Comics)
- Back to the Future: The Ride (Doc Brown's Chicken was situated near the Institute of Future Technology)
- Back to the Future: The Game