BURG A VAN DEN (2002) The decline of the Eurasian Sparrowhawk Accipiter nisus on the SW Veluwe: caused by predation or food shortage?. LIMOSA 75 (4): 159-168.

During the last decade, the Eurasian Sparrowhawk population of the Veluwe, the largest continuous woodland area of The Netherlands, has declined by 50%. One hypothesis is that this was caused by a decrease in food supply for Northern Goshawks A. gentilis which caused a higher predation pressure of Northern Goshawks on Eurasian Sparrowhawks. However, it is also possible that food availability for Northern Goshawks and Eurasian Sparrowhawks co-vary, which may also lead to a reduction in Eurasian Sparrowhawk numbers. The present paper analyses these two possible causes based on data from 1991-2000, collected on the SW Veluwe. If predation is an important cause, nest success is expected to have declined and predation to be frequent. If food shortage is an important cause, it is expected that females are unable to produce eggs and that prey choice has changed. The population decline was especially pronounced in the low grade forests of the SW Veluwe, relatively poor in breeding passerines. Ring recovery data and the age of newly recruited females in the breeding population suggest that increased mortality caused the decline. However, the percentage successful nests has not changed from 1991 and only 12% of all nests that had young were not successful due to predation. These data suggest that predation had only limited effects on population change. Failure to lay eggs in finished nests was most common in poor food areas. Gradually, these territories became vacant. In 1998, an unusual influx of migratory finches Fringilla sp. was observed, resulting in a sharp increase of occupied territories, which only lasted for one season. Although the population of the House Sparrow Passer domesticus has declined, it was taken more often by Eurasian Sparrowhawks as prey, indicating that the hawks hunted more frequently outside the forests. Although these observations suggests that food shortages in the forests are of importance, this is contradicted by a lack of decline in songbird numbers in both rich and poor forests. Perhaps, prey quality is a limiting factor for the number of breeding Eurasian Sparrowhawks in poor forests. At present however, only few data are available that describe the effects of prey quality on avian reproduction.

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