need help, newborn rabbit

Question
WE have two rabbits, and untill this morning we assumed they were both female... but in the middle of the lawn i work up to find a little blackish brown squirming thing, i looked online ans quickly realized it was a newborn rabbit. my first instinct was to look for more!

Just some backround info... the two rabbits live comfortably outisde in the backyard we're in southern california so it dosent get overly hot or cold for them, they seem to be extremly happy!
we have a hutch for them that we can lock them in if need be, they both knwo this is where they find food and water, but other than that they roam free in our bunnie proofed back yard. WE also have a trampoline that they  both like to play underneath and we have foudna  few tunnels underneath...

At first i went to a tunnel under the the trampoline that i thought was abandoned, i stuck my arm down to see if there was anything and proceded to find nothing. i assumed the rabbit just ahd the baby and lost intrest in it. forgive me but this is my first time with rabbit newborns and wasnt ever a plan of mine to raise rabbits. but then later in the day, with the newborn in a box with some towles, i noticed the obvious mother pulling fur form ehr chest and then she dashed under the trampoline and into a hole i had missed
i saw he run back out and then i proceded to see if there were more possible babies at the end of the tunnel, i could not reach so i widened the hole for my shouder to fit in and found an obvious nest, with fur and other random things, so i proceded to put the baby rabbit in the nest and then let it be, thinking the mother will take care of it. Now later in the evening i go to check on things and see the hole plugged up!!
i dig out the hole and find most of the tunnel not flled in , and the one baby rabbit still alive. i figured this was some mechanism used by the mother to keep the baby warm or whatnot, but i dont want the baby to die form lack of air.

Please help !
thanks

Answer
Generally in the wild mother rabbits keep all the babies together in one nest, it's unusual for one baby to be out and away from the rest.  Then again she could have only had the one baby, and isn't sure what to do with it.

As long as the mother can get into the tunnel, and she probably has more than one entrance, I would leave the baby there for her to take care of.  Check periodically to make sure he is being fed.

There's more info about baby rabbits at http://homepage.mac.com/mattocks/morfz/rabcare.html#baby

Kim