The food resource utilisation of six species of Banksia by the endangered Carnaby’s cockatoo (Calyptorhynchus latirostris) was investigated on the Swan coastal plain, Western Australia, over a 12-month period. The energy yield from the seeds harvested by the cockatoos was determined and the information was combined with data on the number of infructescences produced per hectare, the average seed yield per infructescence and the average rate of harvest of that species of seed by the cockatoos to calculate estimates of the number of infructescences required to support a single cockatoo per day under a range of scenarios. Over 65% of infructescences of each species of Banksia handled by the cockatoos were consumed for seed. Banksia sessilis had the largest number of infructescences and follicles manipulated by Carnaby’s cockatoos. The energy content of Banksia seed was 20–23 kJ g^–1. Seed weight varied from 0.075 ± 0.016 (s.e.) g for B. attenuata to 0.007 ± 0.002 (s.e.) g for B. sessilis. The number of infructescences required to meet the birds’ daily energy intake ranged from 14 for B. grandis to 3821 for B. sessilis. The results have important implications for the continued capacity of the Swan coastal plain to support Carnaby’s cockatoos, for the future survival of obligate seeding Banksia spp. and for anthropogenic revegetation programs utilising Banksia spp.