Your tea bush(es) will appreciate the added humidity. 

Why not pair a tall grass with a short(er) grass? One of the things about bamboo is that is tends to attract grasshoppers, when you pair that with more grass, you get more...grasshoppers and birds love eating those hoppy, vigorous bugs that would otherwise unleash havoc on your edible landscape if left uneaten. Bamboo and River Oats create an excellent environment to attract grasshoppers throughout the warm seasons. 

Bamboo's robust root system and evergreen canopy may also provide an excellent home to mice which, if seen by ducks or chickens, will become a snack instead of a garden pest. The River Oats provide additional space for them to hide in, but, in my experience, after your birds find a spot that has something delicious in it, they will return to that spot to look for more food.

The thick and vigorous root system of the horseradish plant and the upright nature of its leaves work together to create the perfect environment for pill bugs and earth worms who love darkness and moisture. 

Earthworms love comfrey due to the robust nature of its roots and its ability to crack open even the hardest of clay soils. By feeding your ducks around a comfrey plant, whatever they leave behind will quickly become worm food.

Also, the comfrey will more than likely get eaten, leaving the River Oats to provide shade and atmosphere until the comfrey grows back, and it will do so, very quickly. 

Tomatoes are very good at attracting the tomato hornworm, which is technically, a caterpillar, not that your ducks or chickens will care about that distinction when they are gobbling the bugs up. Tomatoes are very moisture-loving plants with robust root systems that benefit greatly from being mulched and paired with ground cover plants. Since River Oats are relatively tall-growing, they might hide some of your lower growing tomatoes to keep your ducks or chickens from eating them all, though I recommend just growing a tall-growing or indeterminate tomato and training it up high so there are plenty of tomatoes--and hornworms-- to go around.