Folivores - birds that feed on leaves

Cheong Weng Chun sent me an image of a juvenile Asian Glossy Starling (Aplonis panayensis) with a bunch of young rain tree (Samanea saman) leaflets in its beak. And in his own words, the bird was: "chewing - no, can it chew or perhaps, I should say swallow?"

This started me asking a pertinent question "Do birds eat leave?" Well, some birds do... Anyway, I ended up with some interesting information.

Folivory applies to those birds that eat leaves, either exclusively or partially. Although a successful foraging strategy for numerous species, few birds are exclusively folivorous. Why? Because flight demands an enormous amount of energy and leaves do not provide the necessary energy. The energy content of leaves is only half that of fruits and a quarter that of insects and other arthropods. Also, leaf digestion is slow and requires a large storage space in the gut. Besides, digestion needs to be undertaken by specialized bacteria present in the gut

Those birds that regularly feed on leaves have thus turned to gliding or abandoned flight altogether.

Only about 3% of all birds, from at least 14 families, eat leaves regularly. Most of these birds are terrestrial or aquatic and only 5 families include aboreal members. From these 5 families only 2 species, Hoatzin (Opisthocomus hoazin) and Owl Parrot (Strigops habroptilus) obtain most of their energy from leaves. These include new growth of green leaves, buds, flowers and fruits in season, moss and fungi. Hoatzin is a South American bird whose flight is weak and awkward. It clumsily creeps up branches and make only short flights. The other is a flightless bird of New Zealand.

R. Subaraj notes that certain birds offer leaves during courtship, but we have an immature bird here. So does it mean that its behaviour is precocious?

Image by Cheong Weng Chun