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