In ecosystm breeding occurs when two flocks who are in breeding behavior, co-mingle and decide to produce offspring.

If both flocks are player created flocks, both parties must agree to the union (unless both are in autobreed mode).  If the flocks are offspring flocks, they decide for themselves based on their behavioral rules.

To breed press the keyboard "B" key, switching to breeding behavior, and find a flock who is also interested in breeding.

Flocks who are interested in breeding, will also seek out you, and after a time you should encounter such a flock.  Position your flock to co-mingle with the flock of your desire, and the breeding confirmation window appears.

Here you see the genetic composition of your betrothed, and can choose to accept.  If you chose not to accept you can no longer successfully initiate breeding for that day, however you still can be the object of another flock's attention.

 Each bird's physical size is a measure of its performance.  Birds can be very large or very small.  A flock that is larger than you is performing better, and might be a good candidate, however smaller flocks have the potential to be "good buys". 

When you create your flock, or when two flocks breed to produce offspring,  the flock has an initial performance value of 1.  If the total value of the flock increases (by summing the current values of the 32 unit gene sequence and multiplying by the number of birds in the flock), the performance value increases and your individual birds grow in size.  Please note that in ecosystm.1 (the currency ecosystem), the population of the flock grew, not the size of the individual birds. 

In ecosystm.2 the population grows only under certain circumstances (see POPULATION).