I have ten runners who are about fourteen months old. I have raised them since they were a day old. Love'em!
Not all ducks need a pond. The smaller breeds like runners especially do pretty well without one. I have a couple of
concrete mixing pans for their swimming pleasure.
Large breeds may benefit from a pond when it comes to mating, I am told.
Ducks will eat small fish and other small aquatic animals, based on what I have read and videos I've seen.
When we say "ducks," we are covering a huge territory. There are the tiny, sweet, loud little call ducks and then there are the massive gorgeous white Aylesburies. Also, "pond" can mean many different sizes and configurations (spring fed? rainwater fed? stream fed? any snapping turtles or large mouth bass?).
Plant wise, I have been told ducks will just ruin any plantings you have. That has not been my
experience.
What I have seen is that if you leave runner ducks in an area long
enough, they get the worms and slugs and grubs, then they start nibbling on the greens, and if it's wet, they love to drill holes in the soil looking for more goodies. There are times when they suddenly seem to discover a plant they have left alone. But again, in my experience, it is because they have noodled and foraged and area so much they are looking for something to do and eat.
Ducks enrich their swimming water very quickly. I like the pans because I can dump them into a small channel I made that fertigates a
garden bed downslope. Works great!
I hope this wasn't too much blab. I love ducks. I recommend that if you're going to get them, or even if you already have them, read the good
books and blogs that exist about their care. There are some disagreements on a few topics, but the more I have learned the better the duck experience has been. I like Storey's Guide to Raising Ducks (there's a new edition out now, I am told), and
Carol Deppe has a wonderful chapter about ducks in her book, The Resilient Gardener.