Bird population trends (2003-2011) and landscape and climate change in agroecosystems of Central Argentina: an approach using density estimation from distance sampling and mixed linear modeling

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

Workshop; EURING 2013 Analytical Meeting & Workshop; 2013

University of Georgia

ABSTRACT: Agricultural expansion and intensification recently occurring in Argentina, particularly in the Pampas region, has resulted in important changes in the agricultural landscape. Consequently, biotic populations may have experienced changes on abundance and distribution. In this work, we analyzed the relationship between changes in the density of four bird species (Eared Dove, Monk Parakeet, Fork-tailed Flycatcher and White-browed Blackbird) and environmental variables associated to climate, vegetation cover and productivity for the 2003-2011 period in Central Argentina. The study area consisted of three agricultural sub-regions (predominantly agricultural, agricultural-rangeland and agricultural-forested rangeland). Bird populations were sampled yearly in 48 30-point routes located on secondary roads. Points were separated by 1 km and sampled for 3 minutes, using distance sampling. Density was estimated using three models (uniform, half-normal and hazard rate) and two adjustment terms (cosine and polynomial), and the half-normal model with a cosine adjustment was selected for all species, using AIC. We then estimated the species-specific detection probability function combining all years, and bird density for each route and year by stratifying per year and post-stratifying per route. In mixed linear models, the fixed effects were year (i.e., temporal trend) and environmental variables describing climatic, primary productivity and land cover variation. The random effects were “observer”, “route” and “sampling period”. We also constructed models with a temporal autocorrelation structure and heterogeneity of variances. Using AIC and Akaike weights, models most selected were those with random effects and year-specific heteroscedascity. Mean density for Eared Dove was 11 ind/ha, almost three times higher than the second most abundant species, the Fork-tailed Flycatcher (4 ind/ha). Eared Dove and Monk Parakeet density increased significantly in all areas, while the density of the White-browed Blackbird decreased. The density of the Fork-tailed Flycatcher generally increased, but varied between areas. Although the relationships between bird density and environmental variables depended on the species, plant vigor and proportion of land use (annual crops, annual pastures, perennial pastures, plowed fields, fallow fields and forest) were significantly associated to changes in the density of all species. Based on these results, environmental changes occurring in the region have favored increases in some species and decreases in others. Recognizing these individual differences will be fundamental in establishing more precise and systematic baselines for biodiversity management and conservation at regional scales.