Consists of paired kidneys , drained by ureters into urodeum region of cloaca. No urinary bladder is present. Because it is insoluble in water, little water is required for its excretion. This is an important mechanism for water conservation in birds.
Birds tend to lose more water via evaporation than mammals due to their higher metabolic rates.
May be 200-300X larger than at other times of the year. Vas Deferens - drain testes, also enlarge greatly during reproductive season. Penis - present in Ratites, Tinamous, Storks, and Anseriformes as an erectile grooved structure fixed to the ventral wall of the cloaca. Functions to introduce sperm in the female reproductive tract. Ovary - only the left ovary develops in most birds, but functional right ovaries occur in Accipitridae, Falconidae, Cathartidae, and Brown Kiwis.