Sounds like a typical fox attack to me although I've not heard of a fox killing a bird that big before. We've had flamingos and a white stork killed by them but never an ostrich. Will have to keep an eye on the cassowaries. Unfortunately fox proof perimeter fences are not always feasible and very expensive. We had no problems with foxes at Bristol for the first ten years I was there and then they were everywhere and took 8 flamingos, a white stork, red-breasted goose, palawan peacock pheasant, Pink pigeon and mongoose lemur within a few months. Efforts were stepped up to keep them out but suddenly they were seen all the time within the zoo. Luckily we've had no problems for quite some time and the flamingo paddock has now been meshed over. I don't feel it's fair on the zoo animals for the to have to be shut in every night but sometimes it's the only way...