Will parents eat their young?
You have a father or fathers that impregnate the mother-to-be. The mother balloons and 21-some days later, there's a litter of ratlets squeaking their lungs out in hopes that she'll stop stomping on them and get on with the next meal.
In the wild, the rats live in colonies. There are many females and males, there is an alpha male and there are subordinates. Unlike most of the pet population, many of the subordinates could easily, due to strength, swiftness, and intelligence alone, be alphas themselves but one day they decided they didn't want to die for the position and gave into the guy who calls himself alpha. Rather than fight for the women, they tend to share (with the alphas permission, because, again, they could kill him if they really wanted to) and every litter, then, is generally representative of the group as a whole (more or less). Of course, as we know, rats can be forgetful.
In the wild (and in the pet population), moms are very protective of their young. They are also very dutiful moms and will make sure the babies are healthy and fed. She will try her very best to keep her nest out of harm's way so the nest will be located in colony territory which affords the nest protection but it will be in a quiet and safe place. After all, she also has to venture away from the nest to feed herself.
All of these things ensure the survival of the litter barring other unforseen circumstances and barring these unforseen circumstances, neither mom or dad will eat the young.
But babies may "disappear" anyway.
In the pet population, the number one cause of "disappearing" babies can be explained by considering the health of the babies or the need to ensure the health of the survivors. If mom thinks there's something wrong with one of the bubs, she'll quickly end his life by delivering a puncture wound through the base of his skull. She'll then consume the remains to make herself stronger for the survivors. In the wild this also ensures that the smell of the deceased won't attract unwanted visitors.
On the same line, if the mom gives birth to a substantially large litter, she'll remove the smaller and weaker of the bunch. While I'm sure it's nice to know that you'll have 18 offspring growing up and living in your image (plus, just think of all the refrigerator art!) it's unreasonable to believe that all 18 of them would grow up to be strong, healthy rats who, via their inherent strength alone, will improve the colony as a whole. Mom has a certain amount of nutritious milk to pass on to her offspring and if she can split it up into 12ths instead of 18ths, the 12 will be considerably stronger, healthier, and fatter than the 18 would be. So moms have to sometimes make executive decisions by trimming some of her litter to ensure the welfare of the whole. Moms, if they must make this decision, will do so early on so as to reduce suffering and also to increase her own strength by affording her offspring the best milk possible.
The last common cause in the pet population for disappearing babies is that the mother isn't lactating. She can't feed them and ultimately does the kind thing and ends their lives. Either that or she ignores them, not recognizing that they're her own.
Another option, albeit less common, is situation dependent. A mom will "mercy-kill" the offspring if she doesn't perceive any chance of their survival. If a female rat gives birth in an open aquarium with a snake in it, and if she is aware of the threat of that snake (this awareness is sometimes questionable with the pet rat population particularly when the snake isn't hungry and makes no advances) she'll eat the whole lot of them in order to prevent their suffering (usually she'll puncture their skulls and eat as many as she can while the others will just remain).
If she's in unfamiliar or new surroundings (15 minutes after you brought the pet store rat into your home, she gave birth) she may also consume the whole pack of them. Most of the time, though, rat moms will try to make the best of it. She'd like to raise her kids in a safe environment but it's not that safe so she has to protect them as best she can, after all, one survivor is better than none because one survivor can aid in perpetuating the species. And nests can be built later. It's nice to have them already set up for the occasion, but if the birthing must come first, so be it.
Onto the males...
In the wild you're talking about colonies...families of rats. All the dads remain there the entire time. Unless food is plentiful, you don't need to worry about the moms becoming pregnant the moment she gives birth. Besides, who's going to walk up to a pack of wild rats and tell them they need to be separated into boy burrows and girl burrows so as to ensure the health of mom and the bubs? It doesn't, obviously, work that way: They control their own population based on the availability of food, available space, safety of the territory.
The point is: The dads don't breed with mom and then just disappear. They're there the entire time. So when mom gives birth, they know who she is and they know who her offspring are (who they belong to), and they can all be confident that these babies are part of their family. And we don't eat our families...I hope.
(But, yes, in the wild, sometimes a dad will eat some of their offspring: It is theorized that they're doing their part in ensuring the strength of the colony by eliminating offspring that were fathered by weaker male members of the colony...or, in other words, not by him - the guy doing the eating. But, overall, they will not consume members of their own family and the multiple father routine ensures this.)
Back to the pet population: Usually the dad-to-be and the mom-to-be are put together for the purpose of mating and then separated. Sometimes, after mom gives birth, the "breeder" will put the dad back in with the mom and will become "surprised" when the dad eats the babies. That 21 day separation alienated him from his family: he forgot. As far as he's concerned, those babies aren't, and never were, his. And this makes sense: In the wild, if a male of one colony happens upon a litter of rats that aren't his own, he can ensure the strength if his family lines by eliminating future intruders which keeps "foreign blood" out of their lines. After all, the survival of the colony depends upon the strength, wit, and ability to adapt otherwise the species will just disappear.
And sometimes, after mom gives birth, the "breeder" will put another male in the cage with the lactating mother. Those babies aren't his and he'll consume one, some, or all. Same reason as above.
But again, not always: Most dads don't care and they'll leave the nest alone. After all, moms can be pretty scary when they're trying to protect their young and in a cage environment where food is delivered bedside, mom doesn't have to venture far from the nest and can then do a considerably better job protecting them from jealous dads.
But if you're concerned, it's better to be safe than sorry: Keep dad out of the mom's cage until the babies are weaned. Better yet, give mom at least a 3 month hiatus so she can regain her own strength so the next litter is as healthy as the first....Or just don't breed at all :o)
See, also, Anne's article, Infanticide in Norway Rats
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