Answer:
Because it has a low solubility in water and it is less toxic to the embryo as compared to other forms of waste
Explanation:
1. Developing bird embryos excrete most of their nitrogenous waste as uric acid,there are many reasons of this, one the reason is that it has a low solubility in water and it is less toxic to the embryo as compared to other forms of waste.
2. Birds and many other organisms like reptile excrete nitrogenous waste in the form of uric acid, because it reduces water loss compared to other nitrogenous wastes, but it requires more metabolic energy as compared to others to produce.