Black-naped Oriole (Oriolus chinensis) eats a broad range of fruits. It also takes insects like grasshoppers, mantids, large caterpillars and hornet grubs. And of course bird nestlings.
Dr Redzlan Abdul Rahman documented the oriole manipulating the rolled up portions of banana (Musa) leaves that contain the caterpillars of the Banana Skipper (Erionota thrax).
The Banana Skipper is a large brown butterfly with large yellow spots on the forewings above. The adult is seldom seen but the presence of its caterpillars is made conspicuous by the rolled up portions of the banana leaves.
The butterfly lays its eggs singly on the leaves and when the egg hatches, the caterpillar rolls up the leaf from the tip along the mid-vein, feeding on one edge. The caterpillar develops within the roll, to pupate inside as well. When the adult butterfly emerges from the pupa it leaves the roll.
The Black-naped Oriole has become adept at manipulating the banana leaf roll in an effort to get at the caterpillar or pupa hidden inside. The bird lands on the leaf, garbs the roll with its feet to dislodge it. The roll is then brought to a nearby branch where it is expertly manipulated until the caterpillar or pupa inside is extracted.
The caterpillar or pupa inside the roll normally wriggles violently when disturbed and the bird needs to subdue it before eating. This is usually done by swiping the prey against the branch. Sometimes the caterpillar is passed back and forth between the bill to remove the stomach contents, as observed in the Chestnut-bellied Malkoha (Phaenicophaeus sumatranus) and the Collared Kingfisher (Todiramphus chloris). However, whether the oriole did this was not observed.
An earlier account of a Black-naped Oriole manipulating a cocoon can be reached HERE.