Abundance of invertebrates and foraging success of Black-tailed Godwit Limosa limosa chicks in relation to agricultural grassland management

摘要

Effects of agricultural intensification on availability of grassland invertebrates as food for chicks of the declining Black-tailed Godwit Limosa limosa were studied in The Netherlands. Invertebrates were sampled with photo-eclectors in wet grasslands used for intensive dairy farming (high fertiliser input, 2-3 cuts starting early to mid-May) and in a meadowbird reserve (moderate fertiliser input, one cut in mid-June). Invertebrates were slightly more abundant in reserve than in agricultural fields before the first cut of the latter. In the 4-6 weeks between the first cut of agricultural fields and that of reserve fields, invertebrates were much more abundant on reserve fields. This is the main period of godwit chicks' presence. Mean size of arthropods was similar under the two management regimes, but large Coleoptera were more abundant in agricultural fields early in the season. In a foraging experiment, captive-raised godwit chicks ingested 31% fewer prey per unit time when foraging in cut agricultural grasslands than in uncut reserve fields, a difference large enough to compromise chick growth and survival. Wild broods strongly selected to stay in reserve fields, especially after agricultural fields had been cut, and travelled towards reserve fields over distances up to more than 0.5 km. Preference for reserve grasslands declined from early June onwards. We conclude that postponing mowing dates, in reserves or on farmland by means of agri-environment initiatives, improves feeding and survival conditions for godwit chicks and other insectivores feeding in the grassland sward, in addition to its beneficial effect on hatching success.