The effects of traffic on the density of breeding birds in Dutch agricultural grasslands

The effect of traffic on the breeding density of grassland birds was studied in 1989 in 15 transects along main roads in The Netherlands. Out of It species that could be analysed, 7 showed a reduced density adjacent to the road. There was also a strong effect on the summed densities of all species. Disturbance distances varied between species, ranging from 20 to 1700 m from the road at 5000 cars a day and from 65 to 3530 m at 50,000 cars a day (car speed 120 km/h). At 5000 cars a day most species had an estimated population loss of 12-56% within 100 m of roads, but beyond 100 m > 10% loss only occurred in black-tailed godwit Limosa limosa (22% for 0-500 m zone) and oystercatcher Haematopus ostralegus (44% up to 500 m and 36% for 0-1500 m zone). At 50,000 cars a day all species had estimated losses of 12-52% up to 500 m while lapwing Vanellus vanellus, shoveler Anas clypeata, skylark Alauda arvensis, black-tailed godwit and oystercatcher populations were reduced by 14-44% up to 1500 m. In The Netherlands, with a dense network of extremely crowded motorways, traffic should be considered a serious threat to breeding bird populations in grasslands. Greater case should be taken in planning new roads, and it is important to explore how the present effects can be reduced.