Vogelslachtoffers op de Drentse wegen – een vervolg

Bird casualties were collected on four roads in the province of Drenthe (Fig. 1) between 1985 and 1994. Most species showed pronounced seasonal (Table 1, 2) and yearly (Table 3) variations in number of casualties. These variations reflect territorial activities during the breeding season, foraging along roads (especially vole-eaters during years with low vole numbers), presence of roosts in the vicinity of roads, a rise in numbers following immigration in fall and winter and habitat characteristics along the respective roads. An increase in casualties during 1985-94 was found in Common Buzzard, owls and Jay, a decrease in Grey Partridge, Blacktailed Godwit and gulls (particularly Black-headed Gull). Of the latter species, a considerable decline in breeding numbers was found during the study period (Table 4), as is the case with Grey Partridge and Black-tailed Godwit. Increasing height of plantations along roads also results in declining numbers of victims, because the birds have to increase flying height in order to cross the road. Owls are among the most numerous victims, especially Long-eared Owl and Bam Owl. Peak numbers of casualties among owls were found in 1991, a year with low numbers of Common Voles. Presumably, the owls concentrated along roads, where vole numbers were less depressed than in farmland. No correlation was found between breeding numbers of Bam Owls and number of casualties (Table 5). During winter, mainly young Bam Owls fall victim, during summer mostly adult birds.