Epsilon Archive for Student Projects

Abstract

Intensified cultivation of farmland is widely recognized to act negatively on many organisms, including birds as the Skylark (Alauda arvensis). During the last decades, this species has been showing a population decline of about 50-75 percent in northwestern Europe, including Sweden. One important factor that is considered to be a key driver of this decline is the switch from spring- to autumn-sowing of cereals. This change in farming practice has been shown to reduce food availability for skylarks and other species that rely on crop fields for foraging and nesting. To improve this situation, skylark plots (SPs), i.e. small (16-20 m2) unsown patches within winter cereal crops, have been developed in Great Britain during the last decade. The idea with SPs is to make it easier for skylarks to forage, since the sparser vegetation in SPs makes it easier to find food (i.e. invertebrates). From Great Britain the method has been shown to work well, increasing the breeding success of skylarks. However, the extent by which SPs contribute to improve breeding opportunities in Swedish arable farmland is unknown. There are structural differences in the agricultural landscapes of Sweden and Great Britain, with a higher relative proportion of spring sown cereals in Sweden. This might indicate that SPs have a lower positive effect when applied in Sweden, since the high proportion of spring cereals (sparser vegetation) makes it possible for skylarks to find food anyway. Thus it is important to study if SPs have a positive effect on skylarks in Sweden, before applying the method in a huge scale.

In this study, the effect of SPs on the skylark territory density in autumn sown fields of wheat was studied. 15 study plots with SPs and 15 control plots without SPs situated on fields of similar size and surroundings were compared; temporal trends of invertebrate activity and vegetation height were used to examine whether the importance of SPs for territory density was there to be found and if this increased towards the end of the breeding season.

The results indicate that SPs have a positive effect on the territory density of skylarks (total breeding season average in SP-sites 3.30 territories/3.14 ha, SE = 1.49; in control-sites 3.19 territories/3.14 ha, SE = 1.82), an effect that becomes clearer as time goes by. This indicates that the presence of SPs is enhancing the breeding season, making it possible for skylarks to produce multiple clutches. Invertebrate activity increased over time, at the same time as skylark territory density was decreasing. However, the decline of skylarks in SP-sites was less relative to control-sites, indicating that SPs makes the availability of food supplies (i.e. invertebrates) to increase. This pattern does also explain why SPs seems to have an increased positive effect as time goes by (increased vegetation density and hence lower food availability). Studies made in Great Britain do, however, indicate that SPs may have a larger positive effect when applied on larger fields situated in homogenous areas, a fact that have to be kept in mind when applying the method in a larger scale.