Diet of Corncrakes Crex crex and Prey Availability in Relation to Meadow Management

Abstract

Land management intensification has caused declines in many grassland bird species. Corncrakes breed in agriculturally managed meadows and are mainly threatened by nest loss during mowing operations, but may also be affected by alternations in habitat and food availability. We analysed faecal samples to identify the diet composition of Corncrakes in a river floodplain in north-eastern Germany and related the abundance of ground-dwelling invertebrates, sampled with pitfall traps, to management practice. The most frequent food sources were beetle imagines (43%) of which one third belonged to the Carabidae family, followed by snails, beetle larvae, spiders and earthworms. Prey length was on average 11.2 ± 9.8 mm (±SD). Gastropoda species and large beetles (>10 mm) were consumed more often compared to their availability at the capture sites of Corncrakes. Invertebrate abundance peaked in June and decreased in the course of the breeding season. Total biomass, species richness, and in particular the numbers of large ground beetles, were substantially higher on sites unmanaged than on sites mown or grazed in the preceding year. Highest invertebrate abundance occurred in the first and second year after management abandonment, but strongly decreased afterwards to a similar level as under annual management. Our results suggest that rotational mowing at intervals of two or three years would be most beneficial for invertebrates. Under eutrophic conditions in floodplains, meadows undergo rapid succession and habitat quality for Corncrakes deteriorates already in the subsequent year after management cessation. Corncrake protection measures, like uncut refuge areas and delayed mowing dates, may also mitigate the negative effects of annual mowing for grassland invertebrates and enhance potential prey resources for Corncrakes in floodplain meadows.