This is not true. I'm a biologist, birds are omnivores and metabolize fat and carbs just fine, and they absolutely do develop subcutaneous fat. Suet and lard are common winter bird feeds for this exact reason. Calories are calories. Protein beyond their daily needs actually won't contribute much...
So I have read a few other threads on this, but my hens are pretty picky eaters. They will not eat alfalfa (soaked cubes or dried), they aren't interested in leafy greens or veggie scraps. They love their feed, which is a 17% protein mash with rolled peas in it, and have not been keen on a...