Bij de dood van een Sperwer Accipiter nisus: geheelde botbreuken, asiels en sterfte

In June 1998, an adult female Eurasian Sparrowhawk was found in the western Netherlands, recently killed by traffic. This bird had survived a tarsus fracture, despite the fact that the tibiotarsus had healed in a slightly twisted way. A review of mortality factors in The Netherlands, based on ring recoveries, shows that many fewer Sparrowhawks were reported as killed by shooting since the 1950s; instead, mortality from collisions with windows and traffic has increased in frequency, and is still increasing, since the mid-20th century. The relative importance of collisions as a cause of mortality among Sparrowhawks is unknown. An analysis of causes of death among Sparrowhawks presented to the Central Veterinary Institute by the public also suggests that traumas from collisons have become a significant mortality factor (but biased in favour of birds found dead near human settlements). Adult Sparrowhawks show a late winter/spring peak in mortality, juveniles in addition a clear peak in August (coinciding with reaching independence after fledging). Of the incapacitated raptors delivered to rehabilitation centres run by falconers in The Netherlands, Sparrowhawks were among the most numerous (with Buzzards Buteo buteo and Kestrels Falco tinnunculus), i.e. in proportion to their abundance in The Netherlands at large. Of the Sparrowhawks, 59% were successfully rehabilitated and released (no data available on their subsequent survival). This figure is presumably biased, because hopeless cases are routinely euthanized upon delivery, and these birds are not included in the statistics. This also holds for other raptor species, in which between 30% and 67% of the admitted individuals could be released after having been treated. In The Netherlands, data on birds with healed fractures are not available, but a large study in Germany and Austria (Wokac 1990) shows that many birds, including raptors, are able to survive after having sustained a fracture.