Spatial Distribution Patterns, Habitat Correlates and Population Estimates of Steppe Birds in Castro Verde


Castro Verde is the main area of cereal steppes in Portugal (ca. 80,000 ha), having international importance for several steppe bird species with unfavourable conservation status. In spring 2006, a large-scale assessment of bird populations in the region was carried out using a simple methodological procedure. The occurrence and abundance of 16 species of steppe birds was estimated in 391 squares (1x1 km) in order to describe the spatial distribution patterns, explore the habitat variables explaining the observed patterns and estimate population sizes. The more frequent steppe species in the region were Corn Bunting Miliaria calandra (present in 78% of the sampling points), Calandra Lark Melanocorypha calandra (29%), Crested/Thekla larks Galerida spp. (29%) and Little Bustard Tetrax tetrax (28%). In terms of estimated population sizes, we confirmed the national importance of Castro Verde for several species, most noticeably Great Bustard Otis tarda, Little Bustard, Calandra Lark and Montagu’s Harrier Circus pygargus. Regarding specieshabitats associations, four groups of species could be identified: a) those associated with fallow land and grasslands, e.g. calandra lark; b) species associated with cereal fields, e.g. Zitting Cisticola Cisticola juncidis; c) species associated with ploughed fields, e.g. Black-eared Wheatear Oenanthe hispanica; and d) species associated with habitat mosaics, e.g. Galerida larks. Although simple, the methodology used permitted the characterization of the present distribution and abundance patterns, and established a baseline for the monitoring of changes in the future.