De Veldleeuwerik Alauda arvensis in een aantal Nederlandse broedgebieden

Skylark populations decreased strongly in the Netherlands and other countries in Europe during the second part of the twentieth century. This development mainly occurred in grassland and to a somewhat lesser degree in arable land. Densities in semi-natural habitats often remained stabile. A number of habitats have been visited. These are: heath, grassland, arable land, uncultivated (setaside) land and bulbfields. The visited places were known as favourable for breeding Skylarks. Some details follow. Heath: Young heath with low vegetation, open spots with grasses, mosses and sand is preferred. Dry heath is dominated by Calluna, wetter habitats often are rich in Erica. The landscape is mainly open, but some places have scattered trees (heigth six to twelve meters), mostly pine, birch and oak. Mowing or sodding is necessary once in ten or more years, in combination with extensive grazing by sheep, cattle or horses. A heath overgrown with high and thick grasses is of lesser or no use for Skylarks. Densities in good heaths for Skylarks are between 25 and 55 pairs per 100 ha. Grassland: Only unimproved grassland presently hold rather high densities of Skylarks. The vegetation must be varied, with differences in heigth; ditches and open spots enrich the habitat. Densities of breeding pairs mostly differ from 25 to 55 per 100 ha. Arable land: Agricultural intensification influenced the densities. Controls of modem managed farmland with cereals and some other crops, demonstrate that the Skylark sometimes still occurs in densities of five to ten pairs per 100 ha. A biological farm with rye held a density of twenty pairs. Uncultivated land (set-aside): Two setaside fields (former arable land) held densities of forty to sixty pairs per 100 ha. Both fields were grazed, respectively by horses or Scotch Highland cattle and are situated in nature reserves. The vegetation varies in height, sandy spots occur. Increase of fallow land could compensate somewhat the losses of other habitats. Bulb fields’. This habitat is typically for some parts of the Netherlands. Bulb farms are among the most intensively managed kinds of agriculture. It is suprising to find the Skylark as a rather common breeding bird in some bulb districts. Nests are situated in the flowerbeds, which are seperated by narrow sandy paths. Bulb fields are comparatively quiet during a part of the breeding season. Densities in some places reach a level of twenty five pairs per 100 ha. It will be clear that the densities in the favourable habitats do not give a clear indicaton of the productivity of the birds. It is known (Donald 2004) that at least two and probably three breeding attempts are required to maintain the level of a breeding population.