Crow facts

What are corvids?

All 120 members of the Corvidae family are called corvids. These include typical black species such as crows and ravens, which belong to the Corvus genus, but also jays, jackdaws, magpies and nutcrackers. The family is most easily recognised by their sturdy legs and beak, medium to large size, and - although they're technically songbirds - their harsh, croaky and even alien-like calls.

Names are very deceiving though. The word "crow" often refers to the whole family, the genus, or to any species with the word "crow" in it. Even worse, Australian magpies aren't even corvids. However, they've evolved to resemble them in both looks and behaviour to fill an empty niche.

The question that gets asked the most

I personally think the much larger size (strangely not mentioned here; the common raven is the largest songbird in the world), tail shape and voice of ravens are the most reliable indicators.
To my fellow Europeans: most of our crow species resemble the American crow, so this is also a useful chart to tell them apart from ravens.

This is not a baby crow!

Along with this image: http://i.imgur.com/vIQ4dWp.jpg , this picture often circulates the internet, including Imgur, pretending to be a crow. It's a corn crake. Completely different order. Not even close.

This is a baby crow

This naked, blind, pooping belly with a beak is not as cute as you might have expected. Like other songbirds, corvids are "altricial", meaning relatively helpless at birth. Animals more independent at birth (like the rail above, but also some mammals such as cows) are called "precocial". Although they can do much more at birth, like see, walk and feed, their development does not go very far. Humans, and to a lesser extent corvids, have a very long period of dependence, which allows the young to develop to a much higher cognitive level.

Are corvids pests?

This is a widespread opinion, but mostly false. Yes, large gatherings can be very noisy and produce unholy amounts of shit, but that's the least we humans should be able to deal with as an increasingly growing and impactful species.

Although there are some endangered corvids, they are doing quite well worldwide, in contrast to many other birds. They are innovative omnivores, and can thus adapt to novel environments and food sources relatively easy. If a certain prey species is rapidly increasing in numbers, corvids can increase predation and thereby prevent them from becoming a pest.

This recent review shows that crows and magpies have no or only a small impact on the population of other birds: http://onlinelibrary.wiley.com/doi/10.1111/ibi.12223/pdf

Are corvids pets?

Short answer: no. They are not domesticated. They will wake you. They will shit on you. They will hide food everywhere. They will be stressed. They will destroy your things. They will annoy your friends and family. And in the darkness bind them.

Take that as an important warning. That being said, it is possible to keep them but it's a lot of work. You should be very knowledgable about them, have plenty of patience and time, raise them from when they're young and be prepared that it most likely won't work out. On top of that, it's illegal to have wildlife as pets in many countries.

Caching

Caching in animal behaviour means hoarding or hiding food items. Most corvids do this, and this is an important reason for their intelligence. They have to know that things keep existing when out of view, recognise how long they can cache different food types so they don't perish, remember where they hid them, and make sure potential thieves don't see them. Some species (like Clark's nutcracker) cache thousands of seeds every year and rely on retrieving them for survival. Unlike squirrels, corvids cache food in small amounts in many different places, so they need to remember countless locations.

Rascals at play

Corvids are very playful, as can often be seen in the wild and all the cool gifs that pass through the front page from time to time (like the hooded crows surfing on a jar lid down a snowy roof). There are three types of play: locomotor, object and social, and corvids exhibit all of them. Playing is a significant activity for intelligent species in order to learn about the world. A long developmental period and dedicated parental care gives young corvids the time to do so. Adults are also very playful, and it is hypothesised that play in a necessary side-effect of highly developed brains, and therefore that animals (including humans) get psychological issues if they're deprived of play.

Are corvids really that smart?

This is another typical question but it's hard to answer because people have very different conceptions of what intelligence is. It realy depends what cognitive ability is being tested, but corvids regularly outperform great apes and and in some cases perform at the level of 6-year-old children!

This image shows magpies doing the Mirror Self Recognition test. Researchers put colourful dots on the sedated magpies, just as is done with primates. When the birds woke up they tried to preen and scratch the coloured area of their own body, and not their mirror image, which shows that they understood they were looking at themselves.

American crows recognice faces

Corvids are very curious, but at the same time easily startled and frightened. When researchers caught crows to ring them, they noticed these crows started swooping down and scolding them. It even seemed like non-ringed crows did it too.

So the researchers performed an experiment. After wearing masks while ringing new crows, they were not scolded when they took off their masks or wore different types. This was the case for ringed birds but also for those that only watched other crows getting caught and ringed. This clearly showed that observing crows learned which faces were threatening. Note that this in no way implies that the ringed crows 'told' the others, as people often infer. This spread of information is a result of social learning: crows observed each other and thereby learn what is dangerous. After several years the researchers put on their masks again and the crow population responded even more strongly, although many of them never saw the masked people do anything bad to other crows. Even other corvid species started scolding them! Social learning is a strong mechanism, and it can explain a lot of human behaviour as well.

Woah Black Betty!

Watch Betty the New Caledonian crow spontaneously bend a piece of wire into a hook to retrieve a bucket with food from a tube, after her mate took the pre-made hooked tool that she was supposed to use.

I tried to not make this post too long, but I will happily make more, and will answer questions in the comments. I made some relevant posts before if you're interested:
Crows and water displacement: http://imgur.com/gallery/Ukxrh
Humans have troubles with this test: http://i.imgur.com/Uad4jtfb.jpg
The subjects I have to put up with: http://imgur.com/gallery/qomy5
If you seriously want to become an animal cognition researcher: http://imgur.com/gallery/OBZ4q
Ravens have the self-control to hold on to a piece of food in order to receive a better one: http://imgur.com/gallery/ppWKPMM
How ravens show affection: http://imgur.com/gallery/Q46Z4iG
Crow solving 8 step problem: http://imgur.com/gallery/ilwe0
Jackdaws follow human gaze: http://imgur.com/gallery/u78JgBx

Feel free to ask questions in the comments and I'll try to reply asap!