General

Rooks belong to the family Corvidae which includes intelligent birds like crows and jays.  Their natural breeding range is Europe and Asia, east Siberia and Mongolia. Many migrate south to winter around the Mediterranean, in Iran and the northern part of the Indian sub continent.

Rooks are gregarious, not only when feeding together but also breeding and roosting together.  These roosts are known as rookeries. They often use the same sites as in previous years and are mostly found in large pines or eucalyptus trees. The males will forage for food in communal feeding grounds several times a day until the young can fend for themselves at three months old.  During the winter months, birds from many rookeries will congregate in winter roosts which may contain up to several hundred birds.

In 1971 Rooks were declared an agricultural pest in the Hawke’s Bay. It is thought around half the population was shot (approx 35,000).  Because of shooting, Rooks displaced and spread more rapidly and established colonies near Miranda, Tolaga Bay near Gisborne and southern Waikato and Northland.

Breeding

In New Zealand the breeding season is August-January.  Rooks tend to build their nests in the tops of very tall trees such as poplars and pines in late August.  Large rookeries may contain several hundred nests.  Nests are large, untidy and made of twigs, leaves, mud and lined with grass.  The female incubates the eggs and is fed by the male while brooding.  The eggs are bluish green, blotched with brown.

During winter, birds from several breeding rookeries will travel up to 20 kilometres each night to roost together at a large or long established rookery, called “parishes”. In the morning they disperse to feeding grounds around their own rookeries.

The Problem

Some people do not consider Rooks to be a pest as they assist in control of insect pests such as army worms and grass grubs, however when the population is allowed to reach significant numbers they can cause extensive damage to crops as their other food supply falls.  Damage to crops and pasture usually only occurs where established rook populations exist and not the occasional bird, however rook populations do increase very quickly if they are allowed to nest.

Rooks show a strong preference for foraging in fields of cereals at all stages of the crop, in recently cultivated land, and in stands of walnut trees. Feeding ranges are influenced by the occurrence of highly preferred foods, with extensive flights being made to walnut trees and to recently tilled fields. The effect of large flocks of rooks is to severely damage or destroy newly emerging crops or pasture.

Rooks in Canterbury

Historically, rooks ranged the Canterbury Plains between the Waimakariri River and the Rangitata River. In 1994, there were 1642 birds, with the largest population occurring on Banks Peninsula. Since then, small populations have been found in Kaikoura and Waikari.

Control

Environment Canterbury organises rook control. Rook control is a specialised task.  The birds are intelligent and unsuccessful control can lead to rooks becoming wary and much more difficult to control. Rookeries can fragment and new rookeries establish. For this reason, occupiers are asked not control them but to inform Environment Canterbury of their presence or any sightings.  Control usually takes place in spring around the rookeries, when young birds are demanding large amounts of food from adults.

Successful control has been achieved to date through a co-ordinated approach involving the use of restricted poisons such as 3-chloro-p-toluidine hydrochloride (DRC 1339) as well as favourable weather conditions, and limited food sources. These conditions may not occur every year, hence effective control cannot be guaranteed every year.

Contact us

Environment Canterbury requires your help in locating rooks and rook nests. If you suspect you have rooks on your property or have seen them anywhere, please inform the Biosecurity Section or the Potential Pest Line on 03 363 9380 or Customer Services on 03 364 9860.  Please do not attempt to shoot or otherwise distrub the birds. Ecan staff will inspect and control birds if feasible at no cost to landowners