The breeding ecology of the Red-tailed Black Cockatoo Calyptorhynchus banksii escondidus was studied in the northern wheatbelt of Western Australia from the austral spring of 1974 to the end of 1981. The usual clutch was one egg, but 8 of 465 clutches were of two eggs, none of which produced two fledglings. The incubation period was 29 days, similar to that of other species of black cockatoo with similar body mass. The nestling period was 80–84 days, nearly 17% longer than the similarly-sized Carnaby’s Cockatoo C. latirostris. The ages of nestling Red-tailed Black Cockatoos may be estimated by comparison with photographs taken of nestlings of known age or estimated more precisely from the length of the nestling’s folded wing. Aging nestlings enables the calculation of laying and hatching dates.