As a Ph.D. student in Ornithology, I was attacked by many species of birds.
Ninety-nine percent of all attacks by wild birds happen when birds are defending their nests. You are too close to their nest. Back away, and the attacks will cease. Sometimes these defensive attacks will start when you are still a good distance from the nest. They are more motivated to attack if they have eggs or chicks. If they are just building the nest, they are less likely to attack, and may just abandon the nest--considering the location too risky.
And the other 1% of attacks? Many species of birds--Eastern Kingbirds, Red-wing Blackbirds, Crows, Ravens--attack hawks and owls, even when the predator isn't near their nests. This is called "mobbing." Smaller birds mob crows. There's a wonderful video on You Tube of an Eastern Kingbird riding on the back of a flying hawk, while pecking it.
Crows can be trained to "mob" people. In one interesting experiment at a University, researchers donned a "Dick Cheney mask, while handling trapped crows. The crows learned to recognize the Cheney face, and later when releassed, mobbed other people wearing the Cheney mask. I don't have direct experience with being "mobbed," so I can't say how common it is. Probably quite uncommon.
Wild birds do not get rabies, so you don't have to worry about attack by a rabid bird.
A bad rap for the birds
It's possible that someone might have tamed a bird, such as a parrot. It might approach you, attempting to land on your shoulder. You might misinterpret this as an attack.
Once I had a pet Ring-billed gull that I reared from an egg. I used to take it out for practice flights. My telephone number was on a band on its leg. When it reached adolescence at the end of the summer, on one of these flights it said "good-bye" and flew off. About a week later I received a call from the campus policeman. "I have a sick bird here with your phone number on it. Is it yours? Do you want to pick it up?" The bird wasn't sick--it was just begging from people on the street, and this was such strange behavior they thought it was sick.
Here's another example of a tame bird getting a bad rap. One of my fellow grad students, Jerry McGahan, was studying the Andean Condor. He had found a chick on a nest in the Andes, and brought it back for study. Now nearly full-grown, he would take it out for an exercise flight on campus around suppertime, when few people were about.
One lazy summer day, a coed had fallen asleep on the campus lawn, and was still there snoozing when Jerry brought his huge black bird, with it's six-foot wingspread, out for a flight. The magnificent bird rose and circled around, then descended to land next to the coed. Perhaps she heard its wings or sensed a shadow, for just as it landed, she awoke in stark terror.
I've heard that ostriches have a nasty kick.
Many kinds of birds, such as gulls and corvids (crows, ravens, and jays) will try to snatch food from your hand or picnic table. In San Francisco Bay, they follow the ferries and cruise ships. If , while crossing the Bay, you hold something in your hand to eat, gulls will swoop down and try to snatch it. Again, this isn't an attack, but many people misinterpret the bird's intentions. I've even had one of the jays of the Western US land on my head while I was popping something tasty into my mouth. At the University of Wisconsin in Madison, house sparrows hop around the tables, looking for scraps.
If freeloading birds bother you, put away the food, or go indoors. At the very least, don't hold it in a way they stand a chance of grabbing it. Like the gulls afraid of the teddy bear eyes, all birds are very visual, very clever, and very fast. They are watching and judging your every move.
There is one bird species, recently discovered, with poisonous plumage.
Some birds like sandpipers fly fast in tight formations. If you are walking on the beach, one of these flocks might pass nearby and frighten you. But it's purely an accident--they meant no harm.
Some feisty birds I've known
If you walk by their nests, Adelie penguins will charge out and attack. Males are more aggressive than females. They will fix their bill to your pants, and beat you on the shin with their hard, bony flippers. If you spend a lot of time among penguins, your legs will soon be covered with little blood blisters (from their bites) which we call the "penguin pox." There's a lot of variation in aggressiveness, depending on the penguin's sex, age, personality, time of year, and so on. Some just flee when you pass by; a few will attack even if you are 15 feet from their nest.
Most kinds of gulls and shorebirds will attack when you walk close to their nests on the ground. Many are colonial; when you enter the colony, all rise into the air and circle, giving alarm calls. It can be frightening and confusing with so much noise. Some of the birds who have nests close to where you are standing will swoop down to peck your head, hit it with their feet, or defecate on you. Once I was in a Forster's Tern colony checking on nests. There were only 11 nests, but the feisty little birds actually drew blood from my scalp.
Ornithologist Don Miller, who often worked with Ring-billed Gulls, had a good defense for these swooping attacks. He wore a pith helmet (like you see in old safari movies). This effectively kept the bird droppings out of his hair (the helmet was splattered with white), and protected his head from blows. But for an added measure of protection, he glued two movable teddy bear eyes to the back of the helmet. It turns out that if a swooping bird sees you are looking, it will be more cautious, and not actually hit you. So the fake eyes make the birds keep their distance. They still swoop, but they won't come close enough to hit you.
South Polar Skuas defecate, swoop and hit like their cousins the gulls, only skuas are a bit heavier and more fierce. Their haranguing cries are pretty distinctive when they attack.
Ground-nesting Killdeers, on the other hand, will try to lead you away from their nest with the "broken wing" display. No attack is involved, just a very convincing job of acting.
My scariest experience with birds
I was out walking alone late in the fall. I noticed the leaves on the trail were quite disturbed, almost as if someone had been raking them. After about a quarter mile, the trail ended at a cliff. Just as I neared the cliff, the woods exploded with sound, and scared me to death. A flock of about 20 wild turkeys took to the air, with their powerful wings slapping against the leaves and branches, making a dreadful racket. It turns out the turkeys had been turning over the leaves, looking for food. They moved silently ahead of me. But when I came to the cliff, they could no longer escape on the ground, so they were forced to fly.
Red-wing black birds are common and pretty aggressive. Since their nests are well-hidden in cattails (or sometimes in fields), you may have no idea you are close to a nest. Swallows can be aggressive, and some nest in groups (colonies).
Geese and swans are very aggressive in defense of nests and young. George Archbald told me of an unusual incident. He had set up a breeding pair of swans (with wings clipped) on a small pond near his home in Baraboo, WI. The pond was part of a small RV park. One day, a man from the park was wading along the shore of the pond, and approached the nest, which was on the far shore from the RV park. The swans fiercely attacked, clubbing him stoutly with their wings. The man, forced into deeper water, struggled to regain the bank. In the ensuing melee, he lost his wedding ring, and was quite angry about the swan attack. But it was really his fault.
Cranes are also very fierce, and have very long, sharp bills. I believe there is one freak case of a crane killing a man, by pecking him in the eye (and into the brain), where the skull is weak. I'm sure the crane was either cornered, or defending its nest or young.
If you pull them out of their Antarctic burrows, Snow Petrels will explosively regurgitate a smelly, bright orange oil over you. It can permanently stain your clothes.
Many birds have sharp toenails for defense, not to mention sharp beaks. Once I visited writer Fran Hammerstrom at her home. She had a Great Horned Owl for a pet, and that day, it was perched on her bare hand. As I entered the living room, the owl became startled, and sudenly dug its long talons into her hand. Fran said, very calmly, "Would you please come over here, and remove these talons from my hand?" She had to repeat several times as I struggled to understand what had happened, and what she wanted. I grasped the talons of one foot with my fingers, and pried them from her bleeding hand, as the owl stood there rigid as a statue.
The bottom line
Fear of birds is greatly exaggerated. Wild birds are quite harmless, for the most part, although some know how to look very threatening. Hitchcock's movie The Birds gave them a bad name. Insects, siders, poison arrow frogs, venomous snakes and lizards, snapping turtles, poisonous sea shells, and toothy mammals are more dangerous, on the whole, than birds.
If attacked, cover your head and move away until they stop. If you are in a gull, swallow, or heron colony--your presence is very harmful to the birds. The uproar will lead to the death of many chicks, especially if the weather is cold or wet. It's essential that you leave the colony immediately.