Voedsel van Klapeksters Lanius excubitor in het broedseizoen

Pellets, impaled prey and pluckings were collected during May-July in Great Grey Shrikes territories in several regions in The Netherlands (Appendix 1). All together, 694 prey items were identified, i.e. 15.8% mice and voles, 8.4% birds, 11.2% reptiles, 0.2% amphibians and 64.2% insects (Table 1). Little variation in choice of prey between regions was found. Because most of the observed territories were situated on heaths, inland sanddunes and peatland, common voles were relatively scarce in the diet, other voles and mice being equally important. Of 62 birds captured, 26% were full-grown, 32% recently fledged and 42% nestling (Table 2). Nest robbing was also evident from the finding of egg shell fragments in one of the pellets. Among the reptiles, only the viviparous lizard was frequently caught. Insects were important prey items by number, but in terms of biomass did not exceed 15% of the diet. Insect prey was normally relatively large and slow-moving, such as dung-beetles, carabids, noctuids (flushed from the vegetation), bumble-bees and wasps. This diet does not differ much from the findings elsewhere in western and central Europe (Table 3). The scarcity of the Great Grey Shrike as a breeding bird in The Netherlands (15-40 pairs) may depend partly on the scarcity of suitable food, such as voles, in their preferred breeding habitats (mainly partly overgrown heaths). Breeding performance there is rather poor, unless voles had a peak year. For example, in peak years on the Veluwe (Central Netherlands) a total of nine pairs produced at least 23 fledglings (2.6/successful pair), as compared to only 14 fledglings by 15 pairs in years with low vole numbers. All together, only 12 out of 24 pairs in this area succeeded in raising 37 young during the period 1974-95, i.e. 3.1 young/successful pair and 1.5 young/pair. Apparently, Great Grey Shrikes preferred to breed in safe, quiet habitats such as heaths, sanddunes (both often protected nature reserves) and military training grounds, rather than in farmland, despite the latter providing a larger food supply.