Presumably that is referring to wild or semi-wild populations, where predation or other natural pressures may be at work.
Despite the stimulation larger numbers often provide, antelope will breed in Zoos with even just a single pair- if both are fertile and of suitable age. The Black Wildebeest pairs at Newquay and (previously) Marwell demonstrate that. Is there a chance Whipsnade are deliberately not breeding from their Roan perhaps.
The Roan have bred relatively recently (in last 2 years I believe) as well have the waterbuck.
The zoo does seem to go through phases with it's antelope breeding. Evidence of this is the gemsbok, who have produced a calf this year after what seems like an eternity, and there was a successful bongo birth last year.
I guess with Whipsnade keeping much smaller numbers of most ungulate species than they used to, that some of their herds nowadays are in reality just small groups with only a few females, which also means births will be fewer also.
There was always confusion over the Marwell Roan (when there were two herds) some were said to be bakerei but I could never tell the difference visually.
The original pair came from Tim Walkers private collection in around 1982.. as i along with P.Bircher (curator).B.Hall (head keeper) and the late Sue Davis (ass head keeper ) collected them. There first house was one that previous housed Addax next to the Giraffe house.
