The lung of birds is the most complex and efficient gas exchanger that has evolved in the air-breathing vertebrates. Lung tissues of the Egyptian hoopoe (upupa epops major) and the European hoopoe (upupa epops epops) which inhabit Damietta governorate in Egypt were subjected to comparative histological and ultrastructural studies. The results showed that the number and shape of the parabronchus, the form of the infundibula as well as the air capillaries (Acs) and the blood capillaries (Bcs) were also differed. The blood gas-barrier (BGB) was thinner in the European hoopoe (migratory species) than that of the Egyptian hoopoe (resident species). The lung of the European hoopoe is very efficient because of the presence of an extremely thin blood gas barrier than that of the Egyptian hoopoe. This could be attributed to the requirement of enormous energy by the European hoopoe which flies for longer distances, and might indicate that the lung components are correlated with the metabolic demands that are in turn set by the behavior and life style of the animal