As hinted by its long, curved bill, the yellow-bellied asity is primarily a nectar feeder, using its elongated, tube-like tongue to probe the wide variety of plant species that have been recorded as its nectar sources. This species also eats small insects and other arthropods (4).
The yellow-bellied asity has been seen associating with mixed species flocks, probably to provide protection from predators (2).
This small bird species is known for its fearless attitude when defending nectar sources from rivals, the male flashing its bright yellow throat at any intruders (2). The yellow-bellied asity will even aggressively display towards humans (2).
During the breeding season, the vivid male yellow-bellied asity will display to the duller female. In flight, the wings of the displaying male make a loud whirring noise. This seems to be made by a needle-like primary feather, which is only present in the breeding male and so is likely to have a role in sexual display (4).
The female yellow-bellied asity constructs a hanging, pear-shaped, globular nest from interwoven sticks and vegetation, with an entrance hole built into the side (5). This species has been observed nesting between November and January (2).