The following was written by a volunteer in response to another's question: Are male cockatiels nippy? The response definitely puts birds' beaking/biting in a different light.
Bird bites can mean vastly different things under different circumstances. All parrots bite, and they bite in various ways. While we should try to avoid biting that is hostile, aggressive, or defensive, it's important to recognize that many bites are none of these things. Some indeed are affectionate, while others simply convey information. Parrots have a whole vocabulary of bites, expressing a wide range of meanings. I would suggest, in fact, that among parrots, biting and beaking are a distinct and highly evolved medium of communication in their own right, as developed and elaborate, rich, varied, and subtle, as their vocalizations and body language. I believe it is not really possible or desirable to extinguish biting of every sort, and if we could (and to the extent we try) the price would be too high, in that doing so would suppress an important and natural channel of communication and self-expression.
To see why biting is so important, consider that parrots, like other birds, stand upright on two legs (one of many interesting features they share with humans). But having wings instead of arms and hands, they use their beaks and tongues for many of the same things for which we use hands and fingers. Most parrots already use one foot as a hand to hold and manipulate objects, so their beak and tongue serve as a second hand, allowing even greater control and deeper exploration. The beak in fact is probably the more important "hand." It has a much stronger grip than the fingers/toes and and very fine control and coordination.
Further, much as our hands and fingers do for us, the beak-tongue complex takes in a great deal of sensory information for the bird. Both beak and tongue have many nerve endings, making them important tactile sensory instruments. They are the bird's most direct and intimate way of knowing its world (and probably one reason you see parrots running their beaks and tongues all over their cages, toys, and whatever else they encounter).
Now when you have an organ that can both exercise fine motor control and has great tactile perceptual sensitivity, it's hardly surprising it should develop into a means of communication. And indeed - again like our expressive hands - the parrot's beak sends as well as receives information. As a form of close-range communication among these highly social birds, biting and beaking express a huge range of emotions, intentions, desires, and other information. No doubt, this medium of communication is important in wild parrot flocks, where you see birds perching very close together, chattering, preening, squabbling and playing with one another. Bites may express affection and trust; they may be playful, taunting, warning, or disciplinary; they may express irritation, anger, fear, and other emotions. A bite may mean "Leave me alone," "Stay out of my personal space," or "Get out of my way!" It may be part of allover preening and mean "I like you," "You are mine," or "Let's play." It may be part of play: "Ha! Gotcha now!!" It may mean "Ow! You snagged a pinfeather! Watch it, buddy!" It may mean, "Hey, I'm talking to you! Pay attention to me!" or "um, ... you were just giving me a head rub a second ago, remember? Hey! HELLO!!??" It may mean "No! I don't want this (food you're offering)." It may be an urgent "Help! Get away from this danger!" or an outraged "You jerk! How dare you!?" ... that barely scratches the surface, but the range of bite/beak meanings is at least this broad. And each of these bites has distinct qualities in terms of its target, strength, duration and/or repetition, and other features. Each usually also has associations with other expressive features of body language and/or vocalizations, as well as a host of other contextual clues, all of which taken together convey a lot of information. One of the things that can be helpful in developing a closer relationship with our birds is learning to know their individual "beak language."
For more interesting information about birds, browse our Reading Room.