The Blue-backed Parrot, Tanygnathus sumatranus, is also known as Müller's (or Mueller's) Parrot, or Azure Rumped Parrot. It is a parrot found the on the islands around the Philippines and Sulawesi (Indonesia).
It is of medium size (32cm), basically green with yellow-streaked wings, a blue rump, and blue wing bends. The head, mantle, wings and tail are darker green, the belly and collar are lighter green. It is sexually dimorphic (most parrots aren't), with the male having a red beak and the female a pale yellow or horn colored beak. There are six subspecies:
- T. s. sumatranus: Sulawesi and nearby islands
- T. s. sangirensis: Sangir Islands and Karakelong. More blue on wing bends and wing coverts, head darker green. Yellow iris.
- T. s. burbidgii: Sulu Islands. Darker green with lighter collar. Yellow Iris.
- T. s. everetti: Panay, Negros, Leyte, Samar, Mindanao. Mantle and back darker, rump and head lighter. Some blue in mantle. Red iris.
- T. s. duponti: Luzon. Dark green with yellow collar. Yellowish underwing coverts. Iris red.
- T. s. freeri: Polillo Islands. More uniform color with less contrast, more yellow on nape. Iris red.
All occur in up to 800m in lowlands and lower mountains; in forest, along forest edge, and some in cultivated areas. Flocks are small and often active at night. Known to eat crops, including corn.