That day we were there about 45 minutes watching them, and chatting with a keeper and others. Mstari and Kiko were often touching each other, rubbing against each other and generally staying close together.
I saw them myself going thru the motions in the summer. Mstari was receptive but I did not see them complete the act - a longtime keeper was saying she thought Mstari would be pregnant by the end of 2018, but I have not been there enough in the last few months to ask others about that or other things.