I think the problem in Cologne was/is that the silverback Kim is very "picky" about the females. He likes two (Gina and N`Datwa) and breeds with them but pretty much ignores the other two (Kibi and Ulca). Thankfully Ulca has been moved now. The zoo should do the same with Kibi as soon as possible since she is wild born and has never bred, she is 30 now and maybe she could have a baby if she were moved to another group.
Yassa,
Perhaps wild born Kibi could be sent to Hannover (proven male, 3 offspring 2004-2006) or Apenheul (new male Jambo has impregnated 2 females already).
Can you give me some more info on gorilla breeding at Koeln:
Any young born lately over there?
Which gorillas are currently at Koeln?