Renal concentrating ability in selected West Australian birds.

1. The osmotic ratio between ' urine' (the supernatant of the ureteral part of the droppings) and plasma has been determined in a number of dehydrated West Australian birds. 2. The U/P ratio was 1-4 in the Emu, 1*7 in two Columbidae (Senegal Turtle Dove and Crested Pigeon), 2-4 in two Meliphagidae (Singing Honeyeater and Red Wattle Bird), 2-6 in three Psittacidae(Bourke Parrot, 28-Parrot, and Galah), 2-7 in the Laughing Kookaburra, and 2-8 in the Zebra Finch. 3. The Na+ and Cl~ concentrations in the 'urine' ranged from 5 to 71 mequiv./l, the K concentration from 92 to 201 m-equiv./l. 4. There seems to be a rather narrow range for die concentrating ability within each family, but the concentrating ability of xerophilic birds differs considerably.