These are all true, but not things that children know or worry about. You are right that it does require some natural experience with birds being skittish around noises or other stimuli.
A better version might be: Five ducks are sitting in a field. A hunter shoots and kills one of the ducks. How many ducks remain sitting in the field?
Or, if you want the answer to be 1 instead of 0 and to be slightly less helpful, “how many ducks remain in the field?”. (The specificity of “sitting” may give a hint that a bit of careful thought is called for.)
These are all true, but not things that children know or worry about. You are right that it does require some natural experience with birds being skittish around noises or other stimuli.
A better version might be: Five ducks are sitting in a field. A hunter shoots and kills one of the ducks. How many ducks remain sitting in the field?
Or, if you want the answer to be 1 instead of 0 and to be slightly less helpful, “how many ducks remain in the field?”. (The specificity of “sitting” may give a hint that a bit of careful thought is called for.)