And then I found this online:
A. Male robins arrive on the breeding grounds a few days to two weeks before the females return. You can tell male robins because their head and tail feathers are very dark black and bright orange in comparison to those of the female. When the first females arrive later, you'll notice their plummage appears faded and drab in comparison to that of the males.
So I guess you would call it a robin stag party?