Excretory System

The pigeon's paired kidneys are metanephric (the most advanced of the three vertebrate kidney types), flat, elongated and lobulated, and drain directly backward through the ureters into the urodaeum, the middle compartment of the cloaca; unlike the frog, the pigeon has no urinary bladder at all. Nitrogenous waste is excreted as uric acid and discharged as a semi-solid mass together with the faeces, a strategy called uricotely that conserves water - an important adaptation, since a bird cannot afford the extra weight of carrying much liquid ur …