Odd guinea pig behavior

Question
I have 2 guinea pigs.  I have had one for about 8-9 months and i just got another guinea pig that is probably about the same age about 3-4 months ago.  Within the last month the guinea pig ive had longer is doing what ive looked up as a mating dance when she purrs and struts her butt on front of my other pig. However i have been guaranteed they are both females. Now today i have noticed that she is now chasing her and mounting her after doing her dance. Is this something i need to be concerned about or is this some kind of senority kind of thing?  HELP!!

Answer
Hi Molly,

This is normal, don't worry. Dominance behaviours - irrelevant of the gender mix - include:

Rumblestrutting (the rumbling and swaying you mentioned)
Nipping
Chasing
Mounting
Butt-sniffing

If she is rumbling, chasing and mounting a lot then the chances are one of them are in heat. It should ease off after 1-2 days if this is the case.

Best Wishes,

- Laura
www.cavy-care.com