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During 1967, rooks at West Melton and Banks Peninsula rookeries selected mainly Pinus radiata for nesting and chose the highest safe sites. Nest construction periods varied from 5 to 20 days, the last nests being completed most rapidly. Eggs were laid between 30 August and 6 November. Rookeries showed significant differences in laying date, apparently resulting from differences in food availability. The size of eggs varied with laying sequence. The mean clutch size was different at each rookery, ranging between 2.9 and 3.8 eggs, a similar value to that obtained by past workers in Canterbury but smaller than that of rooks in Britain. Nestling periods were directly related to brood size. Growth rates of nestlings varied with brood size, hatching sequence, partial brood loss and season. Parental feeding visits were largely independent of brood size and ranged from 1.4 to 3.3 visits per hour. Failure of the embryo to develop accounted for most egg losses. Most nestling mortality resulted from parents killing the smallest nestling before it died of starvation. Breeding success varied seasonally and ranged from 38 to 12.7%. Three and four egg clutches occurred most frequently, but larger clutches produced more fledglings.