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VAN MANEN W (2017) Disappearance of the Hooded Crow Corvus cornix from the West-European winter scene. LIMOSA 90 (4): 145-154.

At the start of the 20th century Hooded Crows wintered widely throughout the West-European breeding range of the Carrion Crow Corvus corone, but gradually they started to winter closer to, or even within, their North Eastern European breeding area (Fig. 1-3). In this article I reconstruct the decrease of Hooded Crows wintering in the Netherlands and Western Europe and discuss what could have caused this change. From paintings we know that Hooded Crows in the Netherlands were common near human settlements. However, in the 1940s the species gradually disappeared from the city scene and soon would decrease or disappear from the coastal areas. During 1978-90, shortly before their total disappearance, Hooded Crows were more common in open agricultural landscapes than in urban areas. It is unclear whether this early habitat shift was related to a general population decline or simply reflects a change in food availability. Ring recoveries revealed that Hooded Crows wintering in Western Europe, originated mainly from the Scandinavian countries, North Western Russia and the Baltic states. Breeding populations in these countries have been stable since 1950 with over a million breeding pairs nowadays. It may be assumed that around 1900 each autumn a large part of this population migrated to their wintering grounds in Western Europe. Since the breeding populations did not change during the 20th century, it can be assumed that Hooded Crows gradually stopped migrating over large distances and probably even may have become resident birds. This may have been induced by increasing food availability in the breeding areas. If this change in migration strategy would have been caused only by deteriorating circumstances in Western Europe (for instance decrease in food availability or increased competition with Carrion Crow), a negative population trend in the breeding areas would have been likely. Global warming could allow the crows to winter further north. In recent literature, most authors agree on a period of warming from 1980 onwards, but also mention longer periods of cooling earlier in the 20th century when Hooded Crows were already disappearing from Western Europe. This makes global warming an unlikely candidate to explain the change in winter distribution. In the course of the 20th century, Hooded Crows started to use urban environments to breed. Since in this habitat food is available throughout the year, living in cities would encourage the crows to become residential. Contraction of the wintering area and decrease in numbers of Hooded Crow started as early as the start of the 20th century, so there should at least be other factors. Between 1900 and 2000 the human population in Scandinavian countries increased almost two-fold and their amount of food waste increased exponentially (Fig. 4), which must have improved wintering conditions for Hooded Crows considerably. Whether changes in agriculture in the breeding areas also have been profitable for wintering crows, remains unclear. It is thus most likely that the increase in edible waste has been the main factor initiating the behavioural change of the crows. Urbanisation by the crows may have accelerated the process. The periodical rise in temperature may have been convenient for the crows, but probably played only a minor role in renouncing their habit of wintering in Western Europe.

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limosa 90.4 2017
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