No they don't. They go into heat on average about every 6 to 10 days. Only during that time will they allow a male to mate with them and can become pregnant.
Thankfully, female guinea pig don't menstruate.
No female bird menstruates. They lay eggs, they do not have live birth, there is no reason to menstruate or anything to do it with.
um no, only female gerbils can
Male gerbils can be neutered, but it is not recomended. Female gerbils should not be spayed. In general male gerbils should not be neutered unless there is a good reason for it.
yes
No, not every female gets her period. If talking exclusively of those who are biologically female there are those who don't have the anatomy to menstruate or their bodies don't produce the hormones needed to have a menstrual cycle. Pre-pubescent girls don't menstruate and women past menopause don't menstruate, also women who are pregnant won't menstruate during pregnancy (sometimes for longer if they breastfeed), and women who have a hysterectomy to remove the uterus.
Spayed female cats and dogs do not menstruate.
Yes. Male gerbils, no matter how old they are, can impregnate female gerbils. Most female gerbils can no longer conceive after 2 years of age. Either way, it's never wise to put a male and female together unless you intend to breed and provide for several litters. Gerbils are not easy to find homes for.
Only if you give them crank.
No I have two female gerbils (Minnie and KE$HA) and KE$HA is clearly older and they get along fine.
I'd be interested to know where you heard that as I've done necropsies on female gerbils and have not found that to be true.
...You are kidding, right? Gerbils are mammals; some of them are male, and some are, well, female. They reproduce the way mammals do.