Weeds as a food resource for farmland birds: what, where and how many should we leave?

Declines in weed populations and weed seed abundance have probably contributed to the decline of granivorous birds on European farmland. Effective management of weed populations to restore seed sources requires that we know which weeds are important foods for birds, and where and how in the farmed landscape seeds are best made available to birds. Weed genera of widespread importance in farmland bird diet include Polygonum, Chenopodium, Poa, Stellaria, Rumex, Cerastium, Sinapis, Taraxacum and Senecio. The seeds of the most pernicious agricultural grass weeds are not widely taken by birds. Birds will choose to feed where seeds are at high density, easily accessible and where predation risk is minimal. For most species, this means that seed provision is best concentrated along field edges but field centre management is also required for skylark, linnet and twite. Seed is best provided on sparsely vegetated ground. Further research is needed to advance from description of weed management practices that are required to help reverse bird population declines to realistic, quantitative predictions of the size of seed populations needed to support known populations of birds. Field studies of distributions of seed-eating birds as a function of seed densities are now providing a better basis for judging which fields, managed in which ways are most likely to attract and support sced-eating birds.