Effects of field management and landscape context on grassland wintering birds in Southern Portugal

Abstract

This study examined the multi-scale effects of farmland management on the assemblages of grassland wintering birds in Southern Portugal, evaluating the potential influences on bird conservation of ongoing transformations in agricultural landscapes. The bird assemblages of 42 grassland fields were characterised and related to three sets of variables reflecting field management, landscape context and large-scale spatial trends. Birds showed responses to the three sets of variables, with variation partitioning indicating that species richness was primarily influenced by landscape context, whereas abundances were mostly determined by field management. In general, high species richness was associated with small patches of arable land, diverse landscapes, high stream density and forest and shrub cover, which probably acted as sources of non-agricultural species to grassland fields. In contrast, fields located in homogenous arable landscapes tended to be species poor, though they were the most favourable for open farmland species of conservation concern (e.g. skylark, calandra lark and little bustard). Old grazed fallows were generally associated with the highest abundances of both invertebrate and seed-eating birds, particularly that of winter visitors. Seed-eating winter visitors were also associated with stubble fields. The results indicated that conservation of Iberian grasslands for wintering birds requires management at both the landscape and field scales. At the landscape level, large blocks of open farmland habitat need to be maintained. At the field level, conservation management should strive to maintain both stubble fields and old grazed fallows. The application of such prescriptions would require a combination of agri-environmental programs and land planning policies, whereby the financial support to individual farmers should be conditional on the maintenance of adequate landscape contexts at larger spatial scales.