SCHOPPERS J (2004) Decline and recovery of the Rook Corvus frugilegus as a breeding bird in The Netherlands in the 20th century. LIMOSA 77 (1): 11-24.

During the 20th century, several national surveys of breeding Rook have been carried out in the Netherlands. Initially, these surveys aimed to collect population figures in order to undertake management measures. Nowadays they are part of national monitoring schemes for breeding birds. Rook were (and are) often considered as a pest species, since they are thought to cause crop damage and breed in colonies in urbanised areas. Heavy persecution (birds shot or poisoned, colonies disturbed) until the 1980s caused a serious decline and the population reached its lowest level around 1970, with about 10 000 breeding pairs left; only 20% of the former population (Fig. 2). In 1977, the species became protected throughout the year, and especially in the 1980s and 1990s, Rook have shown a major population recovery. However, former breeding areas in the western part of the country are still not occupied (Fig. 1), and the species has expanded its range mainly within and around the core breeding areas, where an increase has occurred in e.g. urban habitats. The current (2000) population of c. 64 000 breeding pairs has its main strongholds in the eastern part of the country (provinces Drenthe, Overijssel, Gelderland and Noord-Brabant; Fig. 1). Large colonies (up to 1250 breeding pairs) are often associated with pastures on clay soils, found especially close to river valleys and other water bodies. Regions with an above-average population growth, like Overijssel, Gelderland and Noord-Brabant, all have a high density of modern farms, i.e. the strongest increases have occurred in areas with high manure input, which are supposed to increase biomass of invertebrate food species. Range expansion in the western part of the core breeding area is associated with increasing manure input as well. In addition, breeding opportunities have increased since in many areas new plantations have now reached a suitable height to establish a colony. During the past five years, the population seems to stabilise (at least in the core areas), although an increase is still observed in the number of colonies. This is also expressed by an ongoing decline in mean colony size (Fig. 2). This trend can be attributed to smaller satellite colonies being established in the neighbourhood of large colonies. Such smaller colonies often are a result of (illegal) disturbance of larger colonies. However, with a growing number of smaller colonies, especially problems in urban areas increase as more people are faced with breeding Rook near their property. Locally, management plans have been established to solve problems with Rook by concentrating them at sites where they cause few problems. Elsewhere, protection has become less strict recently, in order to allow population-control measures. Further monitoring will show if such measures have the impact they aim for, and do not cause a further expansion of smaller colonies. Rook Corvus frugilegus

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