I don't have a clue, sorry! I'm very new to Yorkshire Wildlife Park so my knowledge on the place is very limited. Perhaps somebody else on ZC will have your answer and will be kind enough to share?
Not sure about additions, but it's perhaps worth pointing out that these flamingos are not pure Caribbeans but hybrids (to the park's credit they are labelled as such as well), probably Caribbean x Chilean. Given this, it's unlikely they'll want to breed from these birds in the long-term.
