I have been reading about purslane alot lately. It's an edible weed that's very common. It grows like a weed and people often spend hugh amounts of time and effort getting rid of it when they should be eating it. It's high in vitamin E, essential omega-3 fatty acid, vitamin C, magnesium, riboflavin, potassium and phosphorus. Might be a good addition to the micro clover.
Yarrow is worth looking into also. Widely considered toxic and shows up on almost every toxic to animals list. People need to remember that many of the toxic lists are not based on scientific studies of the individual plants, but often hearsay and legend.
http://plants.usda.gov/plantguide/pdf/pg_acmio.pdf
This is an interesting study by the usda on yarrow. in it you'll find yarrow is a important food source for some birds such as the sage grouse. As well as other animals like, Bighorn sheep, pronghorn antelope and deer. Yarrow is often also found in bird nests, such as the common starling. It inhibits the growth of parasites in nests.
A few reasons you might use yarrow for ducks.
1. It is something they don't normally eat. A plus if you want to help keep an area green. I have no experience with ducks eating it, at all.
2. Yarrow is very hardy and is used as lawn substitute. will stand up to foot traffic.
3. Yarrow has wound healing abilities. Staunching flow of blood from wounds. As an anti-inflammatory, pain relief and astringent. Duck feet are vunrable to injuries.
4. It's a soft fuzzy place to lay or walk on. Web foot friendly
5. It repells certain insects. US Army studies show its much better than Deet for mosquitos, sand fleas and ticks for example.
6. Attracts many "good" insects
7. easy to grow, drought tolerant, poor soil