In December 2005 Cheong Weng Chun shared an image of a juvenile Asian Glossy Starling (Aplonis panayensis) with a bunch of very young rain tree leaflets (Samanea saman) in its bill (above left). And in his own words, the bird was: “chewing – no, can it chew or perhaps, I should say swallow?”
On the afternoon of 16th November 2011, nearly six years later, Weng Chun stumbled upon a flock of approximately 50 Purple-backed Starlings (Sturnus sturninus) among casuarina trees (Casuarina equisetifolia sp.) (above right). And they were pecking on the pine needles (above right).
Sun Chong Hong commented that he had seen “Asian Glossy Starling picked leaflets, both green and yellow ones, of albizia (Paraserianthes falcataria) and then dropped them. I could see the actions quite clearly in these stunted trees in my condo It looked like they were playing with the leaves. It left me wondering what they were up to.” He had also seen sunbirds foraging in casuarina trees and added that “I will not exclude the possibility that they were feeding on arthropods.”
Apparently some birds eat leaves. Known as folivores, these birds may eat leaves exclusively or partially. However, 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 specialised 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 arboreal 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 makes only short flights. The other is a flightless bird of New Zealand.
Cheong Weng Chun & Sun Chong Hong