I firmly and unequivocally disagree on your conclusions drawn. The evidence from in situ statistics on both aridland antelope species, just underlines the urgent need to invest in credible ex situ conservation breeding / assurance population initiative for addax (and undeniably for scimitar-horned oryx) in Australasia exactly due to their critical threat status in situ.
Further points:
I) US/AZA facilities have invested in open range concept to be able to maintain large herds of endangered ungulates ex situ (Fossil Rim, Yulee White Oak, new St. Louis out station zoo).
II) ZAA to extend this to other aridland North African wildlife (dama and dorcas gazelle, Somali or North-African ostrich, bustard species, vultures and some of the local Carnivora).
III) Ad finitum: I would as a regional association invest in supporting in situ conservation initiatives to re-establish both species into the wild in range states with existing programs (Morocco, Tunisia and even Senegal) with those that would benefit from in situ conservation programs (Mali, Niger, Burkina Faso, Mauritania, Egypt?, Sudan?). This with both resources, tools and animals.
It would be worthwhile to determine / establish how large both current ex situ populations for addax and scimitar-horned oryx in Australia are at the moment.
BTW: Both addax and scimitar horned oryx live in small family groups (10-25) while the cited and observed large group congregations only occur at optimum conditions just after vital rains in the desert environment. The latter behaviour is due for most ungulates from North Africa where long droughts are interspersed with short rainy season with abundant vegetation proliferation and cover (it is reminiscent how East African herbivores in Sundanese Sudd, Masai Mara and Serengeti migrate and follow the rains and abondance of nutritional resources).
