Do birds have quadriceps and thighs fused into their hips?
This is probably WAAAAY to late to be of any use to you but hey...
So the simple answer is:
Kinda.
You were actually correct to intuit that the femora of birds have a limited range of motion, with most of the limb motion being provided from the &quot;knee&quot;-down.
So you shouldn't animate bird legs the same way that you would the legs of other non-bird animals.
That's not to say that the femur doesn't move - it does but not my much (it typically doesn't extend posteriorly beyond the vertical). Much of the thicc thigh musculature is there for support.