I really need advice for bonding a single rat (somewhere in the 1.5-2.5-year-old range) with a bonded trio. Historically Remy has not liked rats other than her sister, Toga, so we kept the pair in a separate cage from the trio.

Yesterday we got home from visiting some family and noticed Toga sleeping in a cute, silly position in the corner of her cage. It’s a position Remy sleeps in often, so I figured Toga was just copying something she’s seen Remy do. An hour or so later I went to go poke her because she hadn’t left that spot, and she had clearly passed away a few hours ago. It was completely out of nowhere, she hasn’t had ANY health problems since we got her last June, and in the morning she was awake and eating breakfast before we left. Remy gave her a long sniff and a quick kiss as I was taking her out of the cage, so I think Remy definitely understands that Toga had passed away.

Now the difficult part is trying to get Remy in with my three other girls. Remy and Toga are from the Humane Society and originally were in a bonded trio, but they picked on their biological sister non-stop so they had to be separated from her. We have tried intros with one of our girls (before we got her bonded with the other rats in the trio) and it didn’t go particularly well, they would usually start to gang up on her or ignore her completely.

I am not really sure how old Remy actually is, because the Humane Society’s estimate would make her about 1 year and 8 months right now, but both Toga and their other biological sister have passed away in the past 3 months without any symptoms of being sick. Remy’s also starting to go grey a little. But I don’t want her to be kept alone in the off-chance that she has another 6 months-1 year to live.

Does anyone have any tips for bonding a rat that has had problems with bonding in the past? We stress-bonded our last ones with the carrier method and it worked great, but I’m not sure if I should attempt that with Remy or not.