The simplest mathematical models of animal aggregations generally instruct the individual animals to follow three rules:
- Move in the same direction as your neighbor
- Remain close to your neighbors
- Avoid collisions with your neighbors
– from Wikipedia, Collective animal behavior
- Hexagonal board, edge size 7, the “sky” (without 6 corners and center space)
- 120 playing pieces (60 orange and 60 blue “birds”)
Each player gets 60 birds of one color and adds 3 of them to the board according to the following figure.
The aim of the game seems simple: Bring all of your birds in the sky together into one contiguous flock.
However, the flight of the birds is not that simple. You must add new birds to the sky to let them fly together and this is where the competition unfolds.
Players take turns, starting with Orange. In each turn you choose one of the following options:
- add a bird
- let the birds fly
If no legal moves are available, pass your turn.
Add a bird
Place a single bird anywhere, but not adjacent to any other friendly bird already on the board and not into a region controlled by the opponent (see chapter “Regions” below).
Let the birds fly
A single bird or a line of birds move in a straight line, over vacant spaces and must always stop next to another friendly bird and in this way enlarge one or more other flocks. (A single bird can also be referred to as a “flock.”)
You may never split an existing flock.
A straight line of any number of birds of one color may fly in file or side by side.
You may rearrange an existing flock if it is not split and also enlarged after the move.
A bird can have have just arrived through a legal placement, but have no (immediately following) legal move.
If a player’s birds are separated from each other in different regions, i.e. there exists no open path to any other friendly bird, they are removed from the board - they fly away. “Open path” means vacant spaces or spaces occupied only by friendly birds.
The player who made the move can choose which region must be cleared. It is possible that more than two regions are created. Clear any of these regions but leave one region untouched.
It is possible that the opponent is left with a single flock and the game is lost immediately.
Note that usually creating regions and removing birds is beneficial only for your opponent.
There may be a situation where you neither can (or want to) add a bird, nor let one of your flocks fly.
If no action is possible you must pass your turn. If however, birds could possibly be added, but only in regions of your own then you may pass your turn. If both players pass their turn, the game ends in a draw.
You win by ending up with all your birds in one contiguous flock of any size.
Note that the effect of regions is always secondary. If you accomplish a winning formation and simultaneously divide your opponent’s birds into two or more contiguous flocks, each in one region, you win. There is no need for you to clear regions and possibly create a winning position for your opponent as well.