Just got ducks, what the heck do they eat?

That's odd! I don't have muscovies (just domesticated mallard ducks), but mine love eating the Arion (Rufus &/or Ater) black slugs. I'm pretty sure mine eat the leopard slugs (Limax Maximus), as well as the banana slugs.

Maybe it's a muscovie thing? Or just your ducks? (I've noticed not all ducks are the same. The first batch of ducks we had never muddied their water. Then we brought in 2 new ducks that taught the rest how to make their water utterly filthy. Ducks can be quite diverse!)

I think I have found something they should NOT eat - at least in the winter.  My ducks have been having a party in the Jerusalem Artichoke bed.  Digging, nibbling, etc.   I found the drake on his back, pedaling.  the ducks were all digging, quacking excitedly.  Were they high?  Scared me!  I covered as much of the bed as I could with chain link fence and gave them Vit C and Brewer's Yeast in their water for days.  Anybody ever heard of this?

Hi Barbara,

Welcome to Permies. It has been ages since I had ducks, but I have never run into this.

I used to grow jerusalum artichoke in my ducks yard, and they'd often dig around the bases. I never noticed any acting like your drake, though!

Usually when my ducks are "digging, quacking excitedly," it's because they found a lot of bugs in the soil and are super excited about it. I've never seen a drake (or any adult duck) on their back, though!

I would recommend getting them a duck pellet feed formulated specifically for pet ducks. Try to find a brand that is as close to the Mereks Vet Manual guidelines for feeding pekin ducks. Chicken feed is not an appropriate diet for ducks since it does not have the appropriate protein, niacin, calcium, or phosphorus levels that ducks need. I like the Mazuri Waterfowl Maintence feed because it is designed to float on water which is most natural to a ducks diet in the wild.

Ducks don´t enjoy eating scraps quite as much as chickens do, but some good treats include peas, watermelon, berries, and minnows.

making a giant worm bed is an easy way to supply feed for ducks. if this is new to you putting dead wood or even wood chips on the ground the worms will somehow find these spots and multiply like crazy they can easily be gathered from under dead logs and put into a dedicated worm bed or just make a worm bed where there is lots of this stuff laying on the ground. a rotten pile of food scraps and manure could lead to more supplemental feed for ducks just letting flies do thier thing and making maggots. kind of like a compost pile without adding the bulk to make lots of fluffy new compost.  
if you plant eggplant at a certain time of summer there are certain bettles that will swarm to them. let the ducks in for a feast