I didn't know mice often have communal nests:
Female house mice can raise their young with other females in a communalAll a bit socialist of them...
nest. Two or several females pool their litters in one nest and jointly
care for all offspring, even if litters differ by a few days in age. As
the females cannot tell apart between their own young and the offspring
of the other females, they indiscriminately nurse all pups in the
communal nest. If one female has more pups than the others, she invests
the same into nursing but weans more young and therefore has an