Foraging ecology and reproductive biology of the Stonechat Saxicola torquata : comparison between a revitalized, intensively cultivated and a historical, traditionally cultivated agro-ecosystem

Abstract

An effective strategy to reintegrate biodiversity within otherwise intensively cultivated agroecosystems is to create set-aside and wildflower areas. It remains largely unknown, however, whether the ecological performance of an agroecosystem revitalized in this manner is comparable—from a species’ population biology perspective—to traditionally exploited farmland. To address this question we compared, during two successive years, the trophic ecology and breeding performance of an insectivorous, indicator passerine (the Stonechat Saxicola torquata) in a revitalized intensively cultivated farmland (RIC) and a traditional, extensively cultivated farmland (TEC) in southern Switzerland. The chicks' diet and prey abundance did not differ between the RIC and TEC, with orthopterans, caterpillars (Lepidoptera) and coleopterans predominating (approx. 80% of diet biomass). Although Stonechat pairs initiated more broods in TEC than in the RIC, reproductive success (number of fledglings/territory × year) did not differ significantly between the TEC and RIC. The chicks’ condition (body mass) was slightly better in TEC than in RIC, while no such effect could be shown for chick constitution (tarsus length) in either year. The inter-site (RIC vs. TEC) variation fell well within the inter-annual variation of breeding parameters, indicating that environmental stochasticity could be a greater determinant of reproductive output and young quality than agroecosystem type. Although in need of replication, these results suggest that incentives for setting aside farmland and creating wildflower areas within agroecosystems may not only enhance plant and invertebrate diversity, as has been demonstrated earlier, but can also support functioning populations of vertebrates situated at higher trophic levels along the food chain