Changing grass height alters foraging site selection by wintering farmland birds

Abstract

Abstract Grassland is a valuable habitat for many farmland bird species, some of which have declined in Europe. Successful management of this habitat is important to benefit these species. Recent studies have suggested little correlation between food abundance and bird use in grassland; instead providing access to food may be crucial. We tested the importance of manipulating sward height (via mowing) on the distribution of wintering birds in agriculturally managed grass fields using two within-field experimental designs. In experiment 1, we investigated the effect of two treatments (mown once and control). In experiment 2, we investigated the effects of four treatments (mown once early, mown once late, mown early and late, and control). Mown plots supported higher abundances of foraging kestrels, thrushes and starlings. In contrast meadow pipits and grey herons preferred unmown plots with longer grass. These differences are probably explained by differing anti-predation strategies, increased food abundance for species that prefer above-ground invertebrates (e.g. more food for meadow pipits on longer swards) and increased food accessibility on short grass swards (e.g. for starling, thrush spp.). There were limited effects of multiple mowing events on plot use suggesting one early winter mowing treatment may suffice to create favourable conditions for species that prefer shorter swards. Providing grassland heterogeneity should benefit a range of wintering farmland birds. Although we use mowing to change grass sward height, our findings may also apply at other times of year when livestock grazing may be a more practical solution.