Does an outside mother cat abandon the runt of the liter?

we have two outside cats who both had liters two weeks apart, they keep the babies together in the woods, because we needed the boat, they anitially were born in. There must have gotten attacked because now there is only six total kittens there was 8 and the mothers nose is cut. they took all five of the kittens earlier in the day and put them back in the boat, latter that evening i found the runt lying in their old nesting area by itself. why would she leave the runt, is it intentional? or were they too hungry and wanted to get somthing to eat before moving them? like a break!!! i brought the baby to the mama on our porch, she licked it and let it feed. so will she take care of the baby and bring it back to the boat? both mamma's were born outside here as well.