Here's a site I found really interesting, it relates to this topic that pops up pretty often of infanticide.
http://www.ratbehavior.org/CommunalNesting.htm
http://www.ratbehavior.org/infanticide.htm
Why commit infanticide? Infanticide may be committed for a variety of reasons. Many of these reasons indicate that infanticide may be adaptive to the killer. Animals may commit infanticide in order to:

* gain a food resource by consuming the young (the predation hypothesis).
* gain increased access to physical resources like food, nesting sites, or space (the resource competition hypothesis).
* avoid adopting and providing providing care to unrelated offpsring (the adoption avoidance hypothesis).
* bias the sex ratio of the litter
* Adult males may kill a female's young in order to increase his own chances of mating (the sexual selection hypothesis).
* Lastly, infanticide may be neutral or maladaptive (pathological) and may be the product of selection for another type of behavior like aggression, or may be an accident, or may be the result of disturbances in the physical or social environment (see Ebensperger 1998 for re