Crows, Ravens, Rooks, and Blackbirds are often confused with each other (especially Crows and Ravens) but are actually four distinct birds. Crows, Ravens and Rooks are all in the same direct family (Corvids), whereas the Blackbird is a member of the Thrush family.
Here are some detailed specifics if youre interested, from websites to illustrate the differences between:
***CROWS & RAVENS: "Many people use the terms 'raven' and 'crow' interchangeably, but they are actually quite different. Technically, since ravens belong to the crow (corvus) family of birds, they can be called crows - but not all crows are ravens. Corvidae is a family of oscine passerine birds that contains the crows, ravens, rooks, jackdaws, jays, magpies, treepies and nutcrackers (Clayton and Emery 2005, ). Collectively its members are called corvids and there are over 120 species. The two differ in a variety of ways.
First, and most noticeably, ravens are larger than crows. They are (on average) about the size of a hawk, where crows are approximately the size of a pigeon.
If you're familiar with the call which crows make, you'd probably recognize the raven's call as being different. Crows have a more nasal, higher pitched call, where a raven's call is lower, and hoarser... almost a croaking sound. I've frequently been approached by people saying "I heard this really funny-sounding crow the other day..." and when I ask "Was it a really big crow?" the answer has almost invariably been yes. In which case, chances are pretty good that it wasn't a crow at all, but a raven.
If you want to hear the difference for yourself, click here for a raven's call and crow's call.
Crows have a very fan-shaped tail, where raven's tails have more of a wedge-shape to them. This isn't very easy to tell if the bird is sitting on the ground, but when flying overhead, you can often get a good look at the shape of the tail.
Ravens' feathers are also a slightly different shape than crows' feathers. Crow feathers tend to be more rounded at the tip, while ravens have feathers which are slightly pointed. This is most noticeable on the breast feathers, especially when the bird fluffs itself up. The feathers on the crow's breast lie comfortably against eachother and provide a nice, even, rounded covering. The feathers on a raven lie a little more jaggedly, and when a raven fluffs up, its breast tends to look ragged. In fact, when a raven really fluffs up and all its feathers look like they're standing on end, the raven appears to have a short fluffy mane (called a 'ruff').
Ravens and crows can often be found living side by side in the same areas, but where there's a choice, Ravens prefer wilder areas while crows will live quite close to cities. The bigger the city, the less likely ravens will make it their home -- and when they do, they tend to live in or near parks and natural spaces. Crows, on the other hand, are more likely to live near buildings, and will venture farther into human developments to compete for food.
There are more differences between crows and ravens, including their social habits and life span (ravens live longer), but these are the key points. They should help you determine whether the bird you're looking at is a raven or just a very large crow."
***BLACKBIRD is often used as a general term, but that is not proper either since it is a distinct bird as well. Another specific informational page about the blackbird:
"The Blackbird or Common Blackbird (Turdus merula) is a European member of the thrush family Turdidae.
It is common in woods and gardens over all of Europe and much of Asia south of the Arctic Circle. Populations are resident except for northern birds which move south in winter.
Blackbirds are 23.5 to 29 cm in length. They are omnivorous, eating a wide range of insects, earthworms, seeds and berries. They nest in bushes or similar, laying several (usually 4) bluish- green-grey eggs with brown reddish marks in a neat cup-shaped nest.
They do not form flocks, although several birds, especially migrants, may be loosely associated in a suitable habitat. Female blackbirds are especially fierce in the spring when they compete and fight with each other for a good nesting territory. Male birds are also competitive and will protect their territory by chasing away other males. If a fight between male Blackbirds does occur it is usually short and the intruder is soon chased away. Two related Asian Turdus thrushes, the White-collared Blackbird and the Grey-winged Blackbirds are also named as blackbirds.
Larger relatives of the Blackbird in the thrush family include the New World American Robin (Turdus migratorius), the Mountain Robin (Turdus plebejus), and several other species named as robins."
***ROOKS: The Rook (Corvus frugilegus) is a member of the passerine order of birds and the crow family. The species name frugilegus is Latin for "food-gathering".
This species is similar in size (45–47 cm in length) or slightly smaller than the Carrion Crow with black feathers often showing a blue or bluish-purple sheen in bright sunlight. The feathers on the head, neck and shoulders are particularly dense and silky. The legs and feet are black and the bill grey-black.
Rooks are distinguished from similar members of the crow family by the bare grey-white skin around the base of the adult's bill in front of the eyes. The feathering around the legs also look shaggier and laxer than the congeneric Carrion Crow. The juvenile is superficially more similar to the Crow because it lacks the bare patch at the base of the bill, but it loses the facial feathers after about six months."