Forced indoors: are changing cattle husbandry practices turning a rapidly declining bird species into a pest?

Abstract

Increasing farmer complaints about common starlings Sturnus vulgaris depredating maize silage on Danish dairy farms initiated an investigation of whether the growth in larger herds kept indoors year-round fed maize silage was exacerbating this conflict. Agriculture statistics showed a strong positive correlation between maize area and dairy cattle numbers in 81 Danish municipalities, confirming indoor maize silage feeding practices influences maize distribution nationally. Questionnaire returns from large (> 500 dairy cows) farms reported starlings present at 41% of farms where cattle grazed pasture, compared to 78% without grazing (where cattle are fed mainly maize silage). Starling numbers reported in cowsheds highly correlated with herd size and regional starling counts, peaking where large dairy herds were concentrated. Increasing cattle concentrations in large open cowsheds attract starlings to highly concentrated food resources in autumn when birds gather in larger flocks to migrate to winter quarters. Lost grazed grassland to maize production (to provide maize silage to cattle indoors) has denied starlings of invertebrate food formerly derived from pasture, incentivising feeding on cattle maize silage feed inside sheds, escalating conflict with farmers even as starlings continue to very rapidly decline across much of Europe. These conflicts arise from intensified year-round indoor dairy production in larger herds, reliant on nearby maize silage and reduced pasture that formerly supported invertebrate-feeding starlings. These trends have created fewer, high density “hot spots” where both cattle and starlings are concentrated. Mitigating these issues while protecting declining starling populations remains the key research and conservation challenge.

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