Birds being regarded as different animals than dinosaurs. In general fiction, this is excusablehumans are not generally discussed as being great apes, even though they areand in common usage "bird" means "the feathered dinosaurs with adaptations for flight". But if a work discusses birds' or dinosaurs' evolution, it really should come to grips with the fact "birds" are just derived theropods. Similarly, some 'ornithologists' believe that birds have nothing to do with dinosaurs. Their argumentsare best ignored.
Along with the above - birds are reptiles. Birds are modern, non-extinct dinosaurs, and therefore are reptiles. Feathers are highly evolved scales, originally evolved for thermoregulation as opposed to flight. It's significant that the animals living today that're most closely related to birds, are the crocodilians.
Whoever coined the term "eat like a bird" knew very little about ornithology, and depicting them as eating sparingly (or being fussy) is very inaccurate. Birds are actually Big Eaters, some of them eating twice their weight a day because they use up so much energy flying and preserving themselves. These are prey animals (even ones who are themselves predators) so not only do birds have to keep moving to find food, they also have to keep moving to keep themselves safe from predators. To be fast, agile and quick, you need to have energy and that energy comes from food. Birds will constantly eat to maintain that energy so that they have fuel for energy to survive. All of this is taken Up to Eleven during cold winter weather; birds will keep their body temperature right (much better than humans, who are more prone to die to freezing itself, can), but that takes such enormous energy, that they have to eat even more than normal to compensate for that. If they don't succeed in that they die, but they aren't killed by the freezing, they're killed by starvation.
The belief that a bird eating another bird or their eggs is cannibalism, and sometimes birds will be shown freaking out at the concept. A bird eating another bird is the same as mammals eating other mammals, not to mention that some kinds of bird prey on other birds (e.g. eagles, owls, falcons), and there are plenty of birds who eat the eggs and chicks of other species, magpies for example. And let's not get started on the fact that some species of birds indeed have cannibalistic tendencies; chickens are particularly known for this, contrary to popular belief.
The notion that nesting birds will throw any "bad eggs" out of the nest if they haven't hatched is also untrue. Ironically, many female birds, budgerigars for example, will happily eat their own eggs if they are unfertilized, damaged or if the conditions are somehow unsuitable. Some will even do it for no apparent reason at all. After all, an egg (minus the embryo) is basically a container packed with nutrients necessary for the embryo to develop. An egg that's not going to hatch is a waste of resources unless its eaten. Owners of pet birds (parrots, canaries etc.) also feed them egg as a source of protein during molt or breeding.
The belief that feathers evolved for aerodynamic purposes. Accepted as textbook dogma for over a century (albeit with zero evidence), new work conclusively demonstrates that feathers (in the sense of pennaceous feathers with a rachis and barbs) evolved for thermoregulation and display and that flight appeared much later.
Birds are frequently depicted with incorrect toe arrangements. In fiction it is common for all birds to have three toes in the front and one facing backwards, which is known as anisodactyly. In real life there is also zygodactyly and heterodactyly (two toes in the front, and two in the back; known in parrots, cuckoos and woodpeckers), semizygodactyly (ability to switch between anisodactyly and zygodactyly; known in owls), syndactyly (two toes are fused; known in kingfishers, rollers and bee-eaters), and pamprodactyly (all four toes point forward; known in swifts and mousebirds) among others, but in fiction it's likely they'll all have anisodactyl arrangments.
Cartoon birds tend to be depicted with plantigrade feet (ankles touching the ground), due to mistaking their ankles for a "backwards-pointing" knee. Most birds in real life are digitigrade (walking on their toes), although loons and grebes are plantigrade.
Most people think hollow bones like those of birds are fragile. In reality, thanks to a complex honeycomb structure, bird bones are no more fragile than those of mammals. In the case of the now-extinct saurischian dinosaurs and pterosaurs, both having pneumatic skeletons, fragility would mean death, and they obviously had quite strong yet light bones.
It is a very, very common belief that mother birds will reject fallen babies that have been returned to the nest by humans, due to the human scent. A few problems with this:
Very few birds have a sense of smell even worth mentioning (kiwis, albatrosses, and some vultures have a good sense of smell).
Most mother animals don't care if the baby has had contact with humans, unless that contact has been prolonged. Mama Bear wouldn't be much of a trope if mother animals abandoned any and all young touched by strangers.
If humans or other animals are hanging around watching the nest, the parents will be reluctant to return until the "threat" has left.
Disturbed eggs will likely cause parent birds to leave a site for good. The reason being that eggs don't move on their own, and if they've been moved around it's a sign that a predator has been nosing around.
In some cases, the parents (or the other chicks) might have pushed it out of the nest. It could be sick or food could be too scarce for all the chicks. If a chick looks healthy (breathing normally and with no discharge from the eyes or nose) you can attempt to put it back, but there's no guarantee it will stay there. If it's been pushed out again when you get back, either leave it be or take it to a wildlife shelter.
If a young bird seems to be fully-feathered, leave it alone. It's nearly full-grown, and it's very normal for a young adult bird to spend a few days on the ground until it figures out how to fly.
The myth that birds explode when they eat rice due to it swelling inside their stomachs is a case of Critical Research Failure for one important reason: rice is a kind of grain, a common food source for many, many herbivorous birds (and people, too - if this myth were true, we'd get a nasty stomachache every time we ate any rice-based foods). If songbirds, cranes, or pigeons can digest wheat or barley seeds without any problems, why not rice as well?
The belief that ostriches stick their heads in the ground to hide from predators. First off, ostriches don't need to hide and are actually more than capable of fighting off their enemies (they can disembowel a lion with one kick from their hindlegs) let alone being able to simply outrun them. Second, if they did this they would suffocate. It's been suggested that this old wives' tale started by people seeing ostriches investigating the burrows of small animals for food (i.e., that the birds were hunting the current occupants).
Any time ostriches are portrayed with three or four toes on each foot. Real-life ostriches have only two toes, which actually aids them in running.
Ostriches are also commonly drawn with a claw on each toe. In real life, only the larger inner toe possesses a claw.
Female ostriches being black like the males, instead of being gray or brown like in real life. This confusion is maybe due to the fact that ostriches have long eyelashes that are often associated with females.
Birds of prey
The Kidnapping Bird of Prey. Eagles and other birds of prey are light and not capable of lifting huge weights, so carrying off something the size of a human (even a child) would be impossible for them. They can harm and kill large animals (including humans), but not lift them off the ground.
Bald eagles are often shown making the distinctive screeching cry of a red-tailed hawk. They don't do this in real life, instead emitting sparrow-like chirping.
Any time owls are depicted rotating their heads an entire 360 degrees. At most, an average owl can only turn its head about 270 degrees. As for the particulars, owls turn their heads as far as possible one way then turn them all the way in the other direction, they don't simply make a full circle from facing forward like in virtually every depiction.
The common myth about owls being wise is just that, a myth, probably brought about because they appear to be thinking very hard when looking for prey. As it says on that Trope page, they are no smarter than any other bird, and many are smarter.
Portraying buzzards and vultures as one and the same. This may be because buzzard is a term for vultures in the New World.
Due to being scavengers and having ugly appearances, it is quite common for vultures to be associated with bad omen and portrayed as evil. In reality, vultures are the least aggressive of birds of prey (due to being the most social), and their role as scavengers is very crucial to an ecosystem because it prevents spreading of diseases such as anthrax or rabies. Although to be fair, some vultures are indeed ferocious, particularly the bearded vulture which is known to drive large mammals (including humans) off of cliffs, but the better-known species are relatively docile and even helpful to other scavengers.
It is common knowledge that domesticated chickens and turkeys are flightless, but not so much for the fact that this is the contrary for their wild relatives from which they are descended. Wild turkeys are quite agile fliers in spite of their weight, and junglefowl are also capable of flying for a short distance.
Apparently, it is commonly believed in India that peacocks are asexual and the female conceives by drinking the males tear. This belief is not only incorrect, but ironic, because the birds are actually quite promiscuous. The entire reason the male bird fans his feathers is because he's trying to attract as many females as possible.
The common portrayal of swans as kind and gentle birds. Swans are actually very aggressive and territorial, especially when they need to protect their mate and offspring, and a smack from their wings is capable of breaking bones.
For ducks, geese, and other anatids, bread is the Stock Animal Diet in cartoons and movies. It's not healthy for them, though, with little nutrition available; they'd get more mileage out of frozen vegetables or bits of fruit. It's also generally unwise to feed ducks that show up in urban residences, despite tradition - the more they associate us with food, the less afraid of us they'll be, which can make them pests in short order.
Pelicans in cartoons are commonly portrayed as having a giant pouch underneath their bills. In reality, these pouches are only prominent when they're filled up, otherwise pelicans have rather thin and pointed bills.
Pelicans will also be portrayed having only three toes webbed, or no webbing at all. Pelicans, cormorants, boobies, and gannets have all four toes webbed, which is known as a totipalmate foot.
Any time fiction portrays budgies as being in their cages 24/7. This is considered improper and neglectful unless you have a very large cage. (They do better in a small room that's been outfitted for them, with the cage door open so they can use it as their "house".) They need their space outside of the cage, plus it's easier to interact with them outside of the cage. Some pet birds can be left in cages and sometimes it's outright mandatory but many types of birds, such as the aforementioned budgie, shouldn't.
Any work that portrays someone having only one psittaciform bird (a budgie, parrot, conure, tiel or cockatoo, etc.) unless they have it with them 24/7 like a Pirate Parrot. These birds are extremely intelligent and social and need a flock — meaning at least one and preferably more than one other bird (or human) to constantly interact with, or they will literally go insane.
Crackers are the Stock Animal Diet for parrots in cartoons and movies. It's not healthy for them in reality, as many crackers are high in sugars, salts, and fats. Polly would want fruits, nuts, seeds, and meat instead.
Ironically (since they're culturally associated with/in works portrayed as evil, if not outright repulsive), the crow family Corvidae (crows, ravens, jays etc.) are generally harmless to people (except when provoked or defending nests, of course). Corvids are also the antithesis of the common usage of "birdbrain" as a synonym for stupidity, and are actually the most intelligent birds. They're among the few animal species that use tools, they have complex social functioning, and the Eurasian Magpie is the only non-mammal that recognizes itself in a mirror.
Contrary to some fantasy settings (A Song of Ice and Fire seems to be the trendsetter here), ravens and crows don't possess the homing abilities of a pigeon and therefore would be pretty useless as messenger birds.
Magpies do not steal shiny objects to line their nests for a potential mate. In fact, studies show they have an aversion to shiny things due to being unfamiliar to them.
Songbirds and kin
Songbirds don't sing because they are "happy" as many songs and children's cartoons put it. It's usually either to stake out their territories or to attract a mate.
The common portrayal of oxpeckers (i.e. tickbirds) as cleaners for larger mammals have been disputed as of late, since they turned out to be parasites that open wounds on said mammals to lap up their blood. They do eat ticks and fleas though, as one way of getting the blood.
The dodo is popularly described as stupid; in fact the dodo was a member of the pigeon family, which is noted for its intelligence. The reason it died out was because it had no learned fear of humans and no defence against introduced species, particularly rats.
City pigeons being described as wild animals. They're considered feral animals, like feral horses or feral cats, instead of truly wild animals. They're descended from rock pigeons who either got loose or were let go. As a result, they still display a lot of domesticated characteristics (such as a lack of fear towards humans compared to most wild birds).