Winter diet of Yellowhammers Emberiza citrinella on contemporary farmland: the different contribution of forbs, wild grasses and cereals in semi-natural and agricultural habitats

Abstract

Capsule Composition of Yellowhammer diet differed significantly between two major habitat categories: semi-natural (fallow lands, abandoned grassland and road verges) and agricultural habitats (managed fields, stubble fields and manure heaps). Semi-natural habitats and winter stubble fields were important sources of non-cereal plant food and plant parts of cereals were the staple diet in fallow lands, managed fields and manure heaps.Aims To determine the composition of the winter diet and food niche of Yellowhammers feeding on various farmland habitat types characteristic of lowland agricultural areas in Central Europe.Methods Diet was determined on the basis of faecal sample analysis. Multivariate analysis of variance, principal component analysis and two measures of diversity (Shannon Diversity Index and Berger–Parker Index of Dominance) were used to assess the variation in contribution of various plant parts of dicotyledons (henceforth referred to as forbs), wild grasses and cereals in the diet.Results Dietary composition differed significantly between six types of farmland habitats, as well as between these habitats pooled into two major habitat categories: semi-natural and agricultural ones. Plant parts of cereals (grain fragments and husks) were the staple diet in fallow lands, managed fields and manure heaps and were the sole items consumed in crop fields. Plant parts of dicotyledon weeds were eaten almost exclusively in semi-natural habitats. The contribution of wild grasses was highest in stubble fields. The most diverse diet was in fallow lands (road verges > manure heaps > abandoned grasslands > stubble fields) and the most simple in managed fields. Overall diet diversity was positively correlated with the proportion of parts of forbs (dicotyledonous weeds) and negatively correlated with the proportion of pooled fragments of wild grasses and cereals.Conclusion Semi-natural habitats and winter stubble fields are important sources of non-cereal plant food for Yellowhammers. In particular, unpaved roads and fallow land support dicotyledonous weed seeds (Polygonum spp.), and manure heaps contain cereal plant food (probably both husks and seeds from the faeces of farm animals and straw used as litter in their bedding). Contemporary changes in weed communities as a consequence of intensification of agriculture that has reduced this flora to certain abundant nitrophilous species (e.g. Polygonum spp., Chenopodium album, Echinochloa crus-galli and Setaria spp.), the seeds of which are often consumed by Yellowhammers, can therefore increase the food resources of granivorous birds. A mosaic landscape with crop-free plots and microhabitats (with patches of permanent vegetation like road verges), stubble fields (with natural regeneration of annual weeds) and manure heaps enables Yellowhammers to find local feeding grounds, especially during periods of thick snow cover, when feeding sites or resources in open farmland are inaccessible.