Density and reproductive success of Skylarks Alauda arvensis on organic farms—an experiment with unsown Skylark plots on autumn sown cereals

Åke Berg,Olle Kvarnbäck

doi:10.34080/os.v21.22613

Abstract

Skylark plots (unsown plots; 10–25 m2 per ha) in autumn cereal fields have had positive effects on Skylark density and reproductive success on conventional farms in Britain. We tested if the same effect could be found in organic farms in Sweden by comparing paired fields with and without unsown plots in similar settings. We found that the plots had no effect. Skylark density was only associated (negatively) with field size and not with occurrence of Skylark plots, vegetation structure, yield or weed harrowing. Number of clutches per territory was affected by yield (negative) and vegetation cover (positive) but not by Skylark plots. Number of fledglings per clutch showed negative association with yield and visibility through the sward. The amount of weed was larger near Skylark plots from the preceding year than in other parts of the field. The yield (and probably vegetation density) was lower on these fields than in conventional autumn sown fields, but still negative effects of the crop (yield levels) were found.

Highlights

The widespread and rapid declines in farmland bird populations in Europe (Tucker & Heath 1994, Siriwardena et al 1998, BirdLife International 2004) has been attributed to the intensification of agriculture (Chamberlain et al 2000, Donald et al 2001a, Gregory et al 2005)
Most farmland bird populations have probably declined in numbers due to reduced survival or reproduction caused by factors such as loss and degradation of habitats, food supplies or nest sites (Newton 2004)
Skylarks are found in high densities on seminatural grasslands and set-asides (Berg & Pärt 1994, Poulsen et al 1998, Chamberlain et al 2000, Donald et al 2001b, Henderson et al 2000, Toepfer & Stubbe 2001, Eraud & Boutin 2002) and prefer an intermediate vegetation height (15–60 cm)

Summary

Introduction

The widespread and rapid declines in farmland bird populations in Europe (Tucker & Heath 1994, Siriwardena et al 1998, BirdLife International 2004) has been attributed to the intensification of agriculture (Chamberlain et al 2000, Donald et al 2001a, Gregory et al 2005) This includes, for example, simplified crop rotation, more homogeneous and dense crops, loss of semi-natural grassland and non-farmed residual habitats, and increased use of fertilizers and pesticides (Stoate et al 2001, Robinson & Sutherland 2002, Newton 2004, Wilson et al 2005). A probable reason is differences in management, vegetation structure and vegetation height on different types of fields in different areas (Donald et al 2002)

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