It looks like the Mallard landed in the Bear Pool by mistake, but bears aren't natural predators of semi-tame Mallards so it didn't react quite as quickly as it might have with e.g. a dog, otter or Fox. It seems confused but it does try to take off again but its too late by then. The bears seem to just play with it and hardly harm it at first, during which time it 'freezes' with fear, but its obviously 'curtains' for it by the end.
The heron video is very poor quality- maybe it landed on the wall by mistake- a bad move...

The male Lion seems to leap up and catch it but a lioness then grabs it and runs inside- that seems to promote a scrap between them with the male trying to get it back. What happened to the heron seems unclear. The chief interest to me is how the crowd immediately get very excited.
I once saw a partgrown Peafowl chick (already feathered and able to fly) fly across a watermoat into a Gorilla exhibit. The male Gorilla approached but the chick stood its ground and the Gorilla wouldn't touch it.