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 5.9 ± 5.8 m (19 ± 19 ft).
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.

One field study found that red wattlebirds foraged for longer periods when nectar concentrations in flowers were low, and consumed fewer insects at this time.
However, this could have been because the temperature was lower and hence insects were less active.
In Gingin, Western Australia, 97% of red wattlebirds at a site of two mixed kangaroo paw species were observed feeding on a single species at its peak flowering: cats paw in August and red-and-green kangaroo paw (A. manglesii) in September, with very few visits to the other species or hybrids.

In central New South Wales, the red wattlebird forages more often on the foliage of the grey gum (Eucalyptus punctata) over other trees, though it does also show some preference for narrow-leaved ironbark (E. crebra), if grey gum is not present.
Red wattlebirds tend to oust noisy friarbirds (Philemon corniculatus) where both species are present.
The red wattlebird often forages alongside the New Holland honeyeater (Phylidonyris novaehollandiae), little friarbird (P. citreogularis), western and little wattlebirds, rainbow lorikeet (Trichoglossus moluccanus), purple-crowned lorikeet (Glossopsitta porphyrocephala), satin bowerbird (Ptilonorhynchus violaceus), pied currawong (Strepera graculina), and crimson rosella (Platycercus elegans), though they generally chase other nectar-feeding birds away from a horde of eucalypt flowers.

A field study, conducted in winter 1978 on Kangaroo Island, found red wattlebirds to be territorial around a rich source of nectar, namely a large cup gum (Eucalyptus cosmophylla), driving off smaller honeyeaters.
This indicated that the species would exclude other species, if food was scarce.
In New England National Park, red wattlebirds would be more aggressive when there were moderate amounts of nectar in groves of flowering banksias, but were less so at lean or abundant times.

The red wattlebird has a brush-tipped tongue, with a  17 mm (⁵⁄₈ in) long segment bearing around 120 individual bristles.
It feeds by placing the bill in a flower and inserting the tongue into its nectar chamber, drawing the nectar up by capillary action.
The bristles increase the surface area of the tongue available for the uptake of nectar.
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 5.9 ± 5.8 m (19 ± 19 ft). 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.
One field study found that red wattlebirds foraged for longer periods when nectar concentrations in flowers were low, and consumed fewer insects at this time. However, this could have been because the temperature was lower and hence insects were less active. In Gingin, Western Australia, 97% of red wattlebirds at a site of two mixed kangaroo paw species were observed feeding on a single species at its peak flowering: cats paw in August and red-and-green kangaroo paw (A. manglesii) in September, with very few visits to the other species or hybrids.
In central New South Wales, the red wattlebird forages more often on the foliage of the grey gum (Eucalyptus punctata) over other trees, though it does also show some preference for narrow-leaved ironbark (E. crebra), if grey gum is not present. Red wattlebirds tend to oust noisy friarbirds (Philemon corniculatus) where both species are present. The red wattlebird often forages alongside the New Holland honeyeater (Phylidonyris novaehollandiae), little friarbird (P. citreogularis), western and little wattlebirds, rainbow lorikeet (Trichoglossus moluccanus), purple-crowned lorikeet (Glossopsitta porphyrocephala), satin bowerbird (Ptilonorhynchus violaceus), pied currawong (Strepera graculina), and crimson rosella (Platycercus elegans), though they generally chase other nectar-feeding birds away from a horde of eucalypt flowers.
A field study, conducted in winter 1978 on Kangaroo Island, found red wattlebirds to be territorial around a rich source of nectar, namely a large cup gum (Eucalyptus cosmophylla), driving off smaller honeyeaters. This indicated that the species would exclude other species, if food was scarce. In New England National Park, red wattlebirds would be more aggressive when there were moderate amounts of nectar in groves of flowering banksias, but were less so at lean or abundant times.
The red wattlebird has a brush-tipped tongue, with a  17 mm (⁵⁄₈ in) long segment bearing around 120 individual bristles. It feeds by placing the bill in a flower and inserting the tongue into its nectar chamber, drawing the nectar up by capillary action. The bristles increase the surface area of the tongue available for the uptake of nectar.
Red wattlebird