A member of the crow family, the rook (Corvus frugilegus) is a large, glossy, purplish-black bird, with a prominent, powerful bill. Whitish patches of skin show around the base of its pale beak. Larger than a magpie, it weighs around 400 grams and is 45 centimetres long.
Rooks announce their presence with a distinctive ‘kaah’, and as they fly they ‘caw’ to keep in contact with each other.
The oldest rook recorded in New Zealand was over 11 years old.
Rooks are native to Europe and Asia. They were introduced successfully to Canterbury and Hawke’s Bay in the 1860s and 1870s. At first they spread slowly, but then expanded rapidly in Hawke’s Bay.
Before long, rooks were cursed for damaging fruit, vegetable, grain and nut crops, especially walnuts. However, for much of the year their diet consists mainly of grubs, worms and other invertebrates. While searching for these they sometimes tear big tufts of grass or seedlings out of the ground.
At one time rooks were accused of attacking and killing lambs – but this was never substantiated.
Rooks generally nest in colonies of 20–150 nests, often in pines and eucalypts. They lay three to five pale greenish-blue eggs with brown blotches, but usually just one or two chicks survive to fledge.
When not breeding, rooks gather in roosts of up to 5,000 birds, known as parishes, and feed in large flocks.
By the 1960s numbers had increased to pest levels. Early control measures – shooting and poisoning – led to displaced birds starting new colonies much further afield, and so actually increasing their range.
Rooks on the rampage
The Hawke’s Bay Regional Council’s webpage about rooks says: ‘Rooks are the most destructive introduced birds known to our farming sector, due to the sheer numbers of birds in congregations and that may vary from the Hundreds into the Thousands, these birds are able to strip crops in a matter of days. The flocks of rooks foraging of paddocks for grass grub and worms can leave paddocks looking like mobs of pigs have been through them.
‘During their breeding season rookeries are built near houses or woolsheds and the noise from the rooks is intense and very unwelcome to any household.’ 1
In the 1970s an estimated 35,000 rooks were killed – maybe half the population at the time.
Farmers in the Hawke’s Bay region try to deter rooks with scarecrows, ‘crucified’ dead rooks, machines that make intermittent banging noises, bright flapping objects and ground poisoning.
Regional councils use helicopters to carry a person on a long strop to spray individual nests with a sticky toxin, which birds ingest when preening.
Changing distribution and numbers
Rooks’ range in the North Island has expanded since the 1980s. In the early 2000s the main population was in Hawke’s Bay and northern Wairarapa.
In the South Island, their range declined over the same period due to effective control. The Canterbury Regional Council aims to eradicate rooks entirely from its area, and numbers fell from over 5,000 in 1993 to 23 birds in 2005. Banks Peninsula, once a rook stronghold, reported none from 2000 to 2006.