Predicting the effects of agricultural changes in central Spanish croplands on seed-eating overwintering birds

• Published in: Agriculture, ecosystems & environment ecosystems & environment, 1994-07, Vol.49 (3), p.289-298
• Main Authors: Diaz, M. (Complutense Univ., Madrid (Spain). Dept. de Biologia Animal), Telleria, J.L
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Animal and plant ecology; Animal, plant and microbial ecology; Animals; Aves; BESOIN NUTRITIONNEL; Biological and medical sciences; BIRDS; CEREAL CROPS; CULTIVOS DE CEREALES; Demecology; ESPAGNE; ESPANA; Fundamental and applied biological sciences. Psychology; General agroecology; General agroecology. Agricultural and farming systems. Agricultural development. Rural area planning. Landscaping; General agronomy. Plant production; Generalities. Agricultural and farming systems. Agricultural development; GRAINE; LAND USE; NECESIDADES DE NUTRIENTES; NUTRITIONAL REQUIREMENTS; OISEAU; PAJAROS; PLANTE CEREALIERE; SEEDS; SEMILLA; SPAIN; UTILISATION DES TERRES; UTILIZACION DE LA TIERRA; VEGETACION; VEGETATION; Vertebrata
• ISSN: 0167-8809; 1873-2305
• DOI: 10.1016/0167-8809(94)90058-2

The application of the European Common Agricultural Policy is causing traditional crop cultivations to be abandoned over large areas of central Spain. This study tries to assess the effects of these changes on overwintering seed-eating birds by examining how changes in land use could affect winter seed abundances and vegetation structure. Bird densities were measured in the winters of 1985 and 1989, and seed densities and vegetation structure were measured in 1989, in five major habitat types (grasslands, old fields, growing crops, stubble and ploughed fields). The food requirements of birds and the abundances of seeds were transformed to a common energy currency (kJ 10 ha −1) to allow direct comparisons. Estimated winter food requirements were on average an order of magnitude smaller than seed abundances across the five habitat types, and the between-habitat distribution patterns of seed abundance and food requirements of birds did not match at all. Bird abundances tended to be inversely related to herb biomass and shrub cover, which were much larger in uncultivated habitats. From the results obtained, we would expect a decrease of the overwintering seed-eating bird populations in the area if the decrease in cereal crop is maintained. This decrease appears to be due to the increasingly constraining role of vegetation structure (which probably affects food accessibility and perceived predation risk) that would outweigh the larger seed abundance offered by uncultivated habitats relative to croplands.