Birds on roadside verges and the effect of mowing on frequency and distribution

Published source details Laursen K. (1981) Birds on roadside verges and the effect of mowing on frequency and distribution. Biological Conservation, 20, 59-68.
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Summary

New instructions for roadside verge management, taking in to account conservation needs (whilst not compromising road safety), were being prepared by the Danish Road Directorate in the late 1970s. To assist in the process, the effect of summer mowing on bird use was studied in the counties of West Zealand and Ringjøbing (eastern and western Denmark) along seven stretches of verge pairs (1.7-4.7 km in length; 1.3-4.3 m wide).

Summer mowing: Pairs of verges (i.e. on alternate sides of the road) were mown (rotating blades on a hydraulic arm mounted on a tractor) in June/July as follows: the entire left road verge cut; the right cut to the width of one mower pass (about 1 m) along the roadside edge (except where visibility was poor for road users when entire width mown). At one site both verges were unmown.

Autumn mowing: In August/September the full width of all verges was mown (by which time any nesting birds assumed to have fledged).

Bird census: Birds and bird activity were recorded during 31 April to 25 July 1977, using a combination of mapping methods, transect counts and nest searches.

The three most abundant bird species on the verges (making up 74.3% of all individual seen) were skylark Alauda arvensis (209; 32.7%), house sparrow Passer domesticus (199; 31.1 %) and tree sparrow Passer montanus (67; 10.5%). The majority of birds recorded were foraging for food.

The verges proved important nest sites for skylark. Of the 13 nests with eggs/young found, 11 were skylark (one whinchat Saxicola rubetra; one grey partridge Perdix perdix). In addition four incomplete skylark nests were found. Along one pair of verges (2 x 4.7 km long) there were 49 skylark territories. The verges made up less than 4% of a territory, thus expectation of nest discovery (based on area alone) on a verge was one for every 25 territories i.e. a maximum of two nests; eight were in fact found. The verges provided grassland cover whilst many adjacent fields were mostly bare in spring as barley (comprising 68% of crops along the study stretches) is not sown until April-May.

When the summer cut took place there were six active nests, three where a 1-m swathe was cut, and three where the entire verge was cut. Of these, one of the latter was destroyed. Birds preferred to place their nests in at the back edge of a verge (away from the roadside), and this, coupled with the timing of the cut (some nests already fledged) meant most were unaffected by mowing.

Overall, June/July mowing had little effect on bird numbers or their distribution on the verges.

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