Although rabbits are social animals and enjoy friends of their own species, they will typically fight if one rabbit sees another without a gradual process to get acquainted. This process is called an "Introduction".
They have definite ideas of dominance and territory. The Introduction helps them figure out their relationship in a controlled setting so they do not injure themselves and sets the stage for a life-long friendship.
A few rabbits seem to prefer to be the sole rabbit of the household, but these fellows are much less common than rabbits who prefer company of their own kind.
A closely bonded pair (or trio!) of rabbits is wonderful thing to behold. As adorable as rabbits are, they are ten times cuter with a friend they can dote on and be totallly "rabbit" with.
So why aren't all rabbits bonded? Often the rabbit has not found his or her true friend and the humans who witness the tumutuous introduction are too alarmed or afraid of injury to carry on.
House Rabbits Society volunteers have a large number of bonding sessions under their belt & coaching the Introduction is one of the most valuable resources HRS provides.
We show videos of an Introduction that went very well. This is somewhat rare. Keep in mind that a good Introduction is not the end of bonding. When going back home, the established rabbit will be more assertive & the calm of the introduction will not typically last.
These are actions to watch for when bonding rabbits. Abby mounts Chestnut. Chestnut puts up with it a bit. Then tries to get out from under Abby. This leads to a little chase. If Abby were more aggressive she might not run & attack Chestnut instead. This leads to a playful chase. Abby and Chestnut are friends, so this is a safe episode for them, but it could be very hostile if the intentions and trust level were different.