The one mature female rabbit gives birth to one baby female rabbit during the third month. So there is a total of two female rabbits (and several males).

The new chart shows this. At the end of month three there is 1 mature female rabbit and 1 baby female rabbit for a total of two female rabbits.

N | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |

Rabbits | 1 | 1 | 2 |

If you look under month 2 you see how many __mature__
female rabbits there are
in month 4.
Since it takes rabbits two months to become mature,
every rabbit listed for month n will be mature in month N+2.

If you look under month 3 you see how many __total__
female rabbits there are at the start
of month 4.