The Museum of Archaeology and Anthropology (MAA) has an exhibition based on the Star Carr finds. If you're not familiar with it, it is the main source of our knowledge of Mesolithic habits in Britain, including exception finds of deer mask/antler headdresses.
There is normally one on display upstairs at the MAA, but in this special display, they have a mass of them (3D printed copies to protect the originals).
Now you many wonder what the headdresses were for. The display asks exactly that question:
So that clears that up then!
Being the MAA, everything is beautifully and thoughtfully laid out, like this display of worked flint.
They do try to understand the cultural uses of headdress, and where they come up in cultural use, with pictures of a Hupa hunter in California, Talensi dancers in Ghana and the strange parade in some weird place called "Abbots Bromley, Staffordshire" who do the "horn dance". (I found a more contemporary picture in a local newspaper).
I really enjoyed the honesty of "frankly, we have no clue why they made and presumably wore these headdresses". But they were obviously important. It highlights that we're lucky that they were even preserved (the site is already deteriorating and other artefacts are being lost as the ground dries): And we don't even know how many other sites would have had such objects.
Having done my own research, I can say, I don't know how these headdresses are used either, but it is important that we know about their existence - possibly even buy one and try to get into the spirit of your animal self.
(with thanks to FeltYourself)