(Photo: Flickr/L. Bird)
Q: My daughter's hamster ("Sweetie") had babies two months ago. When they were 4 weeks old, we removed the males and put them in a cage of their own. The mother is in the cage with her daughters, and she has begun to attack them. Is there a reason? They were fine together until a few days ago.
A: I am glad to see you did remove the males before you ended up with even more hamsters. Now the reason you have seen Sweetie suddenly become aggressive to her daughters is because hamsters are naturally very territorial. And if the daughters have been with her for 8 weeks, then they have overstayed their "welcome" in her territory.
This is because despite only being fairly new to the world, they are already sexually mature and therefore adults in the hamster world. (Syrian + dwarf hamsters reach puberty as early as 4 weeks). And to Sweetie, they aren't babies anymore. They are competition for territory and resources. So, her behavior is a natural drive to protect her territory and something that we will not be able to naturally override here.
Ideally, we tend to remove all babies from mum after 4 weeks. They of course needed to be separated by sex to prevent inbreeding. And then (again because of their quick maturity), we have to start separating the same-sex groups at 7 weeks to avoid fighting as they feel the need to start establishing territories.
So, this is a natural instinct you are witnessing. In the wild, Sweetie would have driven off her children (now akin to human teenagers) last month, so they could go on their way and find their own territories. And despite being pets, this instinct remains. Therefore, I would strongly suggest rehoming the babies as soon as possible and in the meantime you must remove them from Sweetie's cage before she harms them in front of your daughter.
-- Answer from Dr. B., a veterinarian on JustAnswer.
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