That's the best I've managed this far, one marking spot to go, ended up mating thrice before going in so I was kinda late. In all but a single try so far they've been in Yo Park West which is a helluva tight spot for a herd of angry hippos, I can take a few down on entering and maybe get a mark or two if lucky, and then I have to enter Yo Park East and lose a few of them, but when I get back in they're all there and waiting.
Once I had them spawn at Dogenza, another terrible spot for hippo charges, the streets were basically blocked off by a never ending herd of hippo, forget getting even one spot. So what do I do? Gamble the system and try to get a lucky D-Challenge district, because that one usually tells where the unlock species spawns? What district should I aim for? I've tried stealth and combat but these hippos are as lethal as their real life counterparts. I gotta get my ostrich on :(