rescue GSD bites tail of another GSD - what does it mean?

[gatit48o]

Hello,

We are in the process of determining if we can rescue 2 White GSD's (litter mates/7yrs old spayed and neutered). They are in foster care in Albuquerque because their owner died of cancer back in January and the remaining family could not keep them.

We currently have 2 female, spayed GSD. One white (8yrs old) and one black/cream (10yrs old and definitely alpha - she raised my 8yr old and they get along very well). We lost our White GSD male about 3months ago.

We are slowly introducing the 2 in rescue to the 2 we have. I noticed a behavior I had not seen before in the female rescue and want to query and see if you can explain it. All 4 dogs were all doing well together, sniffing, running a bit, etc. Then the female rescue grabbed the tail of my alpha female (Cassie). Cassie re-acted and the rescue female did too, which caused my white GSD (Nikita) to try to intervene / protect Cassie. The rescue male stayed out of the entire incident. On the positive side when we yelled 'no' the rescue female backed down completely; mine did instantly too.

Can you explain the tail grabbing by the rescue female? Is this a behavior we should be concerned about?

thank-you
debbie friedman