Most herbivorous flying pokemon, such as Natu, use their wings for reaching tall trees in order to eat leaves and fruits and as a means of locomotion. Yet the long neck possessed by Tropius is more than sufficient to reach anything in the forests they call home, and their wings come in addition to four perfectly working legs. Nor do their wings offer any obvious advantages, such as escape from predators; this pokemon's slow acceleration and the canopies of the forests they call home make it difficult to escape. For this reason, Tropius wings had long been seen as the ultimate in useless ornamentation, a body part counterproductive to survival in the modern era.
Yet in this era of massive deforestation, the Tropius have spread their wings, and people throughout the tropics have been greeted by enormous Tropius flocks which cover the sky. They do not go north to south with the seasons like birds, but fly east or west in search of healthy forests where they can make a new home. A brave few are even moving into temperate forests and subsisting off their neck bananas until they can determine which of the local fruits are edible. While other tropical pokemon have become severely endangered, the Tropius population appears to have remained stable, although accurate surveys remain difficult because their locations have shifted massively.
Tropius need their wings because Man is not a new plague on the environment, but has only sped up a natural process which could fairly be called the mother of extinctions. The climate has never been truly static. No forest is eternal. And when a forest dies, the Tropius, unlike so many other species, have always managed to find another.
