During 1954–65 at Canberra, stomach contents of 1319 black-backed magpies of known age, sex and social status were examined. A wide range of ground invertebrates is eaten, mainly insects supplemented by spiders and earthworms. Seasonal fluctuations in diet correspond with the observed abundance of some species, and the effects of weather on others. There are differences between territorial birds in savannah woodland and flock birds in open pasture; the latter showed a higher intake than the sedentary territorial individuals. Observations have been made on the rate of digestion of some food items.