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Rooks are black birds that are approximately the same size as magpies. Adults are totally black except for their face, which has light-grey skin bare of feathers. Juvenile birds have a black-feathered face. Rooks have long, pointed black beaks and dark-brown eyes. They fly with steady wing beats.
This species will nest in colonies, usually in eucalyptus, pine or macrocarpa trees, and they have been recorded in Norfolk pines and Acacia species (brush wattle etc.). They usually travel up to 10km from their night-time roost to feeding sites, but in the breeding season they forage within a few kilometres of the rookery. The main foods of rooks are invertebrates, especially fly larvae and adult beetles and larvae (grass grub) during warmer months.
Rooks lay up to 7 eggs between August and October and the females incubate the eggs for 15-19 days. The male feeds the female and nestlings, which fledge at between 26 and 38 days. Generally, rooks start to breed at between 2-3 years of age. The longest living banded rook in Hawke’s Bay was about 15 years old.
Rooks can cause serious damage to farms and market gardens as they feed on most types of crops, either the seed heads or pulling out young plants. They occasionally pierce fruit such as apples and pears with their bills. Rooks can also tear up large areas of pasture looking for invertebrates.
The species may also have a negative impact on soil invertebrate populations where rooks are in high densities, with this being their main food source, and in turn any native species which rely on these invertebrates as a food source.