Mike,
I definitely agree, however some of the green – yellow hybrids like this one are typically large enough to eat a day-old chick with no problem, but like you said, are probably not large enough to handle a duckling. If it is refusing rodents for this long, it is acting more like a green than a yellow. I have never had a lot of luck starting greens on mice or rats, and they will typically take birds much more readily. I have seen greens refuse rodents until they were in a weakened state, and then take a chick immediately the first time it was offered.

Kelly