Last night I noticed that my 4 week old duckling is now limping. She doesn't like to put a lot of weight on her left leg. She didn't even want to paddle with it when I let her bathe this morning. I looked and felt around and can't find anything wrong. How long should I wait before taking her to a vet? I'ev also noticed that within a few days, that fatty blob at the bottom of her neck has pretty much disappeared. Is that normal for ducks her age, or should she still have a bunch of fat there? While swimming, she was definitely sinking in the front end and I ended up having to hold my hand under there so she could float.