Will a donkey protect a flock like it would a calf? I am considering playing with some free range chicks for eggs for the farmers market. You know have to do something in retirement. I know a dog can be trained to not chase the birds but I don't know how to train them and looks like one slip up could be huge loss.
The only donkey experience I have is knowing a friend that has had up to 3 donkeys at one time (she also has chickens). She says the donkeys are great at letting them know when someone comes on to their property but they don't really watch over the other animals, just the property. You're right about the dogs, they have to be very well trained to counter the prey drive. There are way too many stories of the family pet attacking/killing chickens. I know they can be trained and there are probably posts about that here on BYC. If you want to go with a dog, you might try searching to see what comes up (using the search bar under the logo).
Most donkeys stomp anything smaller than them. I've had pasture guard donkeys kill every chicken I had. There are exceptions, but I don't think I would use a donkey to guard chickens.