I watched a video about the birds a while back, the researchers said the birds don't seem to have any awareness of the overall shape they make, each bird is just paying attention to the nearest (maybe) 5-7 birds and doing what it can to not crash into them.. this makes it a near constant change in direction to wherever they'll fit and not crash.. I'd imagine it's similar with fish (though I think I remember Nova showing sometimes they group up to appear larger to predators, no mention of 'how')

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It is a phenomenon known as "emergence"

It may seem, when you are looking at a flock of birds, that there is some kind of design at work. How does each bird know here to be, how do they keep this v shape? It is particularly mystifying when you see swifts flying in the complex formations they do.

In fact, it is much simpler than that. Each bird is obeying a very simple set of rules:

1. if you cant see another bird then you're the boss. Just fly where you need to go.
2. if you can see another bird keep it constantly at a constant angle and distance to yourself

It sounds simple but if each bird follows those rules then the result is a remarkably organised looking formation. I know this because I have been involved in simulating bird flight for various games and simulations. All it needs is those two rules and you end up with something that looks complex and natural.

Thanks! So what is it, in an individual bird’s consciousness that causes different birds to fly in different patterns. Like geese fly in a V, starlings do whatever the fuck that is, and the swifts that nest in my town fly in a tornado

I'm not a zoologist so cannot give an expert opinion but I have heard that since flying in formation means that each bird is following in the wake of the bird in front of them they may also make adjustments to get the best aerodynamic advantage.

With big birds (e.g geese) this will mean they tend to keep on the same plane as the wings of the other bird thus resulting in a flat 2D formation.

With small birds (e.g. swifts) the nature of the aerodynamics mean that this is not necessary and so they will follow another bird at any angle within the 360 x 360 hemisphere in front of them. This would result in the more three dimensional formations you see with swifts.

The formation also allows the trailing birds to use less and less energy to remain aloft. This is why there is a regular change in the lead bird.

Agreed. One of the common theories is that large migratory birds (geese, swan, etc) fly in formation for the aerodynamic advantage...drafting like cars in a race. The leader will also "rotate" through to allow individual birds to rest. They're able to fly in the correct direction because birds are sensitive to the earth's magnetic fields

Simple rules can produce remarkably complex results, basically.

Many fish, for example, have a pressure sensing organ along their sides called a Lateral Line. If the fish next to them changes direction, they feel it, and can echo it. So if one fish in a school spooks, say, or spots a really tasty-looking piece of food, and decides to change direction, the ones near it feel the change and echo it to avoid collision, and others move to avoid them, and so on. Within a fraction of a second the whole school has echoed it.

Army ants are another excellent example. they have very few brain cell, yet they can join together to form bridges to span quite wide gaps using only very simple rules. If they hit a gap, they slow/stop; and as long as other ants are walking over them, they freeze in place. So basically the first ants to hit a gap stop, other ants clamber over them and stop a little further out, and together they become the units of a bridge that others cross. And once the gap is crossed, they effectively reverse the process, climb out of the gap and tag on at the end. It looks like incredibly complex behaviour, yet invidual ants have almost no instructions to follow.