I have seen this . It is either seasonal or when barometric pressure changes ?
You would think with over 20 years with my clowns that I would know better but I don't !
I will say if sources are correct it is usually the largest that battle and they are supposedly the females .
They usually settle down .I have never lost one from the fighting .
I still have my original 11 that have been with me for 16-20+ years ..