I've had duck a few times in my life and remember it as a nice fatty little bird. The other day I bought a duck at my local Sunflower supermarket. I cooked it in the crockpot and it was leaner than chicken.
What would make a duck lean? Do I want to know the answer to my question?
I think what makes ducks fat is being water birds. The fat helps keep them insulated. But I've read that many farmed ducks do not go in the water. Perhaps they naturally do not develop that protective fat because they don't need it?
But I think it's terrible to farm ducks in this way, just from an animal welfare point of view. Can you imagine, being evolved to fly, paddle around in the water, and forage for bugs at the shore, but being kept in a "battery" at a factory farm? I've been re-evaluating my sources for duck--it's my favorite poultry.
Did you remove the skin before putting it in the slow cooker? I don't usually put the skin of poultry into slow cooker meals (it just seems weird if it's not crispy) and that's where all the fat is on a duck. When I cook duck in the oven I slice the skin so that the fat runs out and crisps the skin up. Very tasty and filling.