The red wattlebird is predominantly a nectar-feeder, foraging mostly in trees; in particular, climbing along branches (rather than the trunk) and probing flower-heads with its bill. One study in Bondi State Forest in southern New South Wales revealed that the species foraged at a height of . They seldom look for food on the ground, though do so to feed on shrubs such as the cats paw (Anigozanthos humilis). The red wattlebird prioritises visiting flowers that produce a lot of nectar, such as those of eucalypts, banksias, grasstrees (Xanthorrhoea), and emu bushes (Eremophila). It often prefers plants with easy access to nectar, rather than those with tubular flowers (and thus difficult-to-access nectar). The red wattlebird seeks out yellow flower-heads of holly-leaved banksia (Banksia ilicifolia), which have much higher nectar content than the more mature red flower-heads. The species forages much more often in native than exotic plants, though the introduced coral tree (Erythrina) is popular. In addition to nectar, it takes insects and other small creatures, usually by hawking, and it also feeds on berries and other fruit. A field study in the Mount Lofty Ranges found that it spent twice as much time feeding on nectar compared to insects.