Bear in mind that Zootierliste was translated from the German and the English names are not always the English standard one (it calls Oryx gazella 'Beisa', for example).
The beginning of my previous comment may not have been as relevant as I originally thought, but the last part was! There must have been a translation error. Generally the name Dama Gazelle refers to the species and an extinct subspecies, but sometimes it is also used for Nanger dama ruficollis. Nanger dama ruficollis is what is commonly refered to as the Addra Gazelle, and Nanger dama mhorr is what is commonly refered to as the Mhorr Gazelle.
These appear to be housed in the old Gemsbok yard (the other side from where the Arabian oryx are now). Do they have access to the paddock to the left of this yard, at all?
As with the mountain gazelle, this species really looks set to disappear from the UK.
Only a few years ago, Marwell had a thriving group of 1.10 Addra gazelle, doing very well in the giraffe house, while Twycross had imported 3.0 Mhorr gazelle, which went to Woburn after a few years. Woburn appeared to lose one not long after they arrived, now ISIS don't list them at Woburn at all.
As for Marwell, ISIS now only list 5 remaining, 2 as generic Dama gazelle. Either the group is just dwindling, or Marwell have been unable to source Addras and have begun acquiring male generic Damas to build a new group. This species has been at Marwell for as long as I can remember (on the small hardstand where the anoa exhibit is now, then the giraffe house), and I hope they maintain a group. I also hope Mhorr's are attempted successfully by a UK collection, I very much regret missing them this time round.