Hey everybody! I'm new to the forum because i'm considering getting a pet rat I currently own a guinea pig, a bearded dragon and a corgi as well. Hopefully this forum will help me make my decision a bit easier.
Welcome! :3 May I first suggest that you get more than one rat, as they really enjoy playing with you as well as at least one of their own species. ^-^ If you need any bit of information or advice then please don't be afraid to ask. xD
After much research, I stumbled on this article:http://www.guineapighub.com/guinea-pig-cages.html that says that guinea pigs may fight with one another if housed in the same cage with insufficient space (more than 10.5 sqft for multiple pigs). I was hoping to keep my guinea pig and rat (possibly 2) in the same cage together, but my cage doesn't meet the "recommended" requirement for multiple guinea pigs. Do you guys think they'll get along fine?
Honestly I wouldn't suggest housing different species in the same cage. They will have different needs (Food, space, etc...) that may not be met because of the joint environment. Also, from what I understand, guinea pigs aren't really suited for climbing and having high hammocks and I would be afraid of the guinea pig somehow making its way up there and falling off.
There are many things wrong with keeping a rat and guinea pig together in the same enclosure.
My biggest concern is that the environmental and housing needs for the two are extremely different. Guinea pigs do great in a large C&C cage with one level whilst rats thrive on being able to climb upwards and make use of large areas of vertical space. As such, a bird style cage works well for rats, but not for guinea pigs. Secondly, there is a high probability that one or both of them may be injured due to size difference alone. Rats have been known to kill other rodents and birds larger than themselves, specifically when they have felt their territory has been threatened. Mixing the two can result in injury or death as you will not be able to supervise their interactions. So, in short - I do not think it is a good idea.
At best a rat and guinea pig may be able to have supervised out time together (though I do not recommend even this) and it really does not help with keeping your guinea pig from loneliness. If your guinea pig cage is not big enough for two guinea pigs than you should look at expanding the one you currently have. You can make a C&C cage quite inexpensively with lots of room and it is a great enclosure for a piggy. Rats are expensive animals and will at some point need vet care costing hundreds/thousands of dollars. If you cannot afford to buy a suitable cage that fits 2 piggies, you cannot afford to keep rats. Sorry, for sounding harsh but literally anybody on this forum will vouch for just how expensive the medical care is for rats.
10.5sq feet is the recommended for male guinea pig pairs, due to their more bossy nature with one another, however 7.5sq ft is the min for one guinea pig, and a pair will often do well in that as well. It depends on their personality to be honest, I have three males, an adult and two babies, in a smaller then recommended cage for a short time and they have no issues. I have another one that has to have at least 12sq ft otherwise he gets grumpy with even his best friend. I don't think there are any species of small animal exotics that can live together... I might have to look that up now, kinda curious. I would get your pig a friend (if you can find rescues in the area many will do meet and greet dates to find one that gets alone with your current. Personalities very so much its a big thing to consider when pairing, or a young baby is easier to introduce if you have an adult. Or a fixed member of the opposite gender is the easiest) and then get a pair of rats if things are good time wise. We have a lot of multiple species and time is much more valuable now then I realized. XD
Good luck with whatever you may end up doing though!