Long-term association of Tyrannus savana and Sturnella superciliaris density with land cover and climatic variables in agroecosystems of Argentina

CALAMARI, NOELIA C., CEREZO, ALEXIS, SONIA B. CANAVELLI, DARDANELLI, SEBASTIÁN, GAVIER-PIZARRO, GREGORIO I. Y ZACCAGNINI MARÍA ELENA

El Hornero

Asociación Ornitológica del Plata

Lugar: Buenos Aires; Año: 2016 vol. 31 p. 97 - 112

0073-3407

Agricultural expansion and intensification are considered two of the main causes of environmental changes worldwide. In Argentina, particularly in the Pampas region, these activities have resulted in important changes in the agricultural landscape. In this study, we analyzed the relationship between changes in bird densities and environmental variables associated to land use/cover, productivity and climate for two bird species, the Fork-tailed Flycatcher (Tyrannus savana) and White-browed Blackbird (Sturnella superciliaris). We used linear mixed models for data collected during 2003-2011 in central Argentina. The study area was divided in three agroproductive subregions: one predominantly agricultural; one mixed agricultural-rangeland and one mixed agricultural-forested rangeland. Bird populations were sampled annually using point-transects located along secondary roads (30 routes in total). Mean estimated density for Fork-tailed Flycatcher was 0.132 ind/ha (±0.01) and significantly increased in the agricultural sub-region. Mean density of the White-browed Blackbird was 0.045 ind/ha (±0.01) and decreased in the agricultural-rangeland subregion. Proportion of land use was significantly associated to changes in the density of both species. Density of the Fork-tailed Flycatcher was associated with decreasing woodland cover and increasing fallow and weedy field cover. The White-browed Blackbird increased in landscapes with more perennial pastures, fallow and weedy fields and annual pastures, and avoided sites with more forest cover. Productivity and climatic variables only showed a strong association with bird density for the White-browed Blackbird. Our results suggest land use/cover, productivity and climatic factors are important when planning strategies to conserve bird population at a regional level in agroecosystems of Argentina.