Alyse asked about where the nestlings get their water...A very good question:
The nestlings get all of their water need met by the food that they are fed. Birds are much much more efficient than mammals in excreting waste products from their systems. Mammal kidneys remove nitrogen forming wastes from the bloodstream and convert these wastes to urea--a poisonous compound that must be diluted in water to form urine. Birds however convert waste products from the bloodstream into uric acid, which is less toxic and can be excreted almost dry. While producing uric acid is much more efficient in terms of water use, it also takes more energy so the birds do pay a price for this efficiency.