Hello and thanks for researching this important question.
Hamsters in the wild are very territorial...this trait has carried into the pet population as well.
A hamster would actually be extremely aggressive toward another animal in its enclosure.
These two species have very different requirements for care and housing and should be kept separately.
Here are some links to sites that give complete details about caring for these two species:
If you need additional support at this time, please click "Reply".
Well, the problems with keeping a guinea pig and a rabbit together are similar: rabbits are solitary animals and can be aggressive. Your guinea pig is male: male GPs can exhibit a lot of territorial aggression as well.
It is always best to keep animals together that can "speak" to each other--understand their social gestures (including dominance) and vocalizations.
Guinea pigs get on best with other guinea pigs...hamsters will not tolerate other species (and can have a lot of trouble getting along with other hamsters!). Mice only like mice; gerbils only like gerbils; ferrets only like ferrets. It's never a good idea to get an animal that doesn't "do it" for you!
If you are interested in other species, it is best to study their special care requirements and plan to house a new pet separately to avoid problems and heartache.
***If you wanted to get your GP a friend, then you might have to consider neutering him and getting a young female companion a month later (when he is completely sterilized and his testosterone level has decreased).***